So the HAA, so the topic here is about the myth of MySQL HAA which is today NLDB because it's the number one topic in how we tackle the high availability and make sure it is always online and easy. So HAA, high availability in MySQL, it has been around for many years. Oh, do you know what is the age of MySQL? How many years? 20? 20? Very close. Very close. Very close. 25 but very close. Another number. 27. Far too much. Yes! Who said that? Oh, you said that. Yes, 24 years old. Okay, by the way, our course, the age is 42. 42 and 22. 24. So HAA, we have been actually doing very good over this so many years in how the redundancy we maintain. So we do replication. Replications, I have data, I pass this to you. I have the data, I pass this to you. So this has to be done a lot of time manually, manually, although this is like, okay, passing the data to the other one. But what about I fail? I'm the master. I fail. Okay, so I have two slaves, master and slaves. I fail, I crashed and the replications will fail because I cannot send the data to the other two. So very often, in this case, the other server has to be promoted, becomes the master. And then the other server, okay, you talk to this guy and grab the data. But who does this? Who does this? Somebody, you! Program is not automatic. That's why we come up with this InnoDB cluster to build this in. And when I actually crash, oh, someone will be promoted automatically. And then this one will handshake to this to get the data directly, automatically. When I recover, I join automatically. And then you have more data than me because you are live. I was dead. And then I come back, I have less data, less data. I have to ask for more data, more online data. And then once I got all the data, I online, I become online and I joined the cluster. So this is automatic. So they are all good. So what are those? Okay, so before going into this, actually I show you one demo. So basically in here, this is just a screen. To show you, I am accessing the database. The access the database is, I can select the data in here, select one or whatever. It doesn't matter just to select a value. So when I do this select value, what I do is, okay, this is working. This is working. Okay? So when I actually select something else, which is select where I connect to. Where I connect to. I connect to a server, which is the host name, my notebook. And the pod number, 3310. Although this is small to you, but I read it to you. The pod number is 3310. But what happens if the server is crashed? But instead of telling you I crashed the server, I try to, the server I need to offline. The 3310. I'm promoting another server called 3320 to be the primary. And what happened this? I go back and then select this again. Okay? What is it? Can you read? Your eyes is good, I believe. What is the pod number in here? That means what? Switched. So when the server crashed, automatic. You see that? So that's the idea. If this is your applications, do you care about the database done? Seems like it's all automatic. So this is the way why we promote this as number one options. And I can do this by switching it back to 1.0 instead of crashing it. Instead, I can crash the server. This is just, I want to bring it back. And I go back and select this again. And the numbers returns here is back to 1.0. Oh, thanks, masters. So let's look at again. So what I'm going to tell is what are those secrets? Now it is a section two. So the beginning, beginner sections, we just talked about what it is. And now into the HA models, how we can work it better. And the next sections after my talk will be the trend about no SQL. How my SQL is working on. So it will be after me. And the last section is everything is done. We need to look at performance. How we monitor how we troubleshoot. So this will be the last section. So back to this one section, we look at the basic and how we deploy. And what are those magic? What are those the magic? So we will go over the basic first example. And things is not just one single data center. Sometimes we need production and also DR. Or we call site failover, site failure. In here, all earthquake, or the building crash, or the room crash, all the power's gone. So maybe another site, the DR has to come up. So how the data, so without the data, DR, the DR data center has no use. Data is a must. Without the data, you know nothing about your customer.  We are all very poor. Or we are equivalent. We are all equal. No more rich and poor because everybody the same. No money. So this is actually NLDB custom vision arts. As a single product, my SQL with HA, and the scaling features, which we can add more nodes, 1, 2, 3, add 1, 2, add 3. And they are all automatic as easy to use. You see, you saw my demo. It is easy to use. And it includes the components, which for sure multiple servers. One server cannot be HA. One machine cannot be HA. So we have to use servers. Multiple redundant server and data has to be automatically transported and exchanged. We have the shell, which I did it. I switched the primary. I switched the server. Okay, so that's the shell. And there is also the router, which is the router in between all the server, all the back ends. And it's like a proxy. The applications is always connecting to this kind of router. And it knows where it has to talk to. So look at this as the basic. We have been talking about master slave replications at the beginning. And we are talking about NLDB cluster in this talk. So what that replication is. The replications, by default, people use asynchronous. It's like posting a mail. The data is written in its own server. And there is binary lock. It's like a data staging area, which is supposed to be sending out. So this is, we call this binary lock. So data is committed only within a single server. And the messenger will come in to pick up the data from the binary lock and send it over to the inbox to the other office, which we call this relay lock. And the relay is just kind of messages in the box. Someone's to pick this up and has to transform this into SQL statement and apply the data back to the database. And our applications, when we use the slave server, we can see the data. That's why when we send the data to the server, we call this master. And then you want to read the data just right after I write the data on the server A, the server B may not have the data. And there is also a point. When the server A is crashed, the last minute data may not getting there because the data is still there. The messenger hasn't come yet. So there is a risk data is gone and lost. And there is also the so-called half-half semi-sync, meaning that when the data is written on my server and I pass to the binary lock on my server, and this also pass to the other side relay lock, when this actually data pass from the binary lock and relay lock, the whole section is acknowledged and committed. So when we commit a data, it has to be here and as well as there. That means we do not have the data loss as what I described in the asynchronous replication. This is called semi-sync, semi-half-half. Why half-half? Because I deliver the data only just the edge on the other box. And the data has to be applied to the server later on. That's why this is half and half. So this is half and then another half, which after applied people can see data on the server. So as what I said, the N-O-D-B cluster is the magic to automate this like the process of sending the data, getting back the data, and promote the database when there is a crash. So this, we have the group replications to exchange data within the group, and they are the members. And there is also application connected router and sending to the back end, which we do not need to care about which is online or done, because it's all automatic. And there is the shell underneath here to maintain how it works. So all this actually within the enterprise edition, we have the graphical GUI and to monitor. No matter what, let's look at deployment example, how this actually may help a company to deploy these H-A models to make sure we are always getting online database and it has to be always be there. So here's the example, at least three server. Why we need three server? One, two, three, at least. Because look at, just you and me, if I crash, okay, for sure you have to be the one serve the data. If you crash, I have to serve the data. But what if in the middle it crash? I mean the network is crash. So are you alive? If I can talk to you, this network is not down. Okay, but the network is down. I cannot talk to you, but somebody can talk to you. Are you alive? You will say yes. And then you ask me am I alive? I will say yes. So both are alive. You write partial data on me and you write partial data on the other. Okay, data is crashed. So that's why two, this split brain effect is no good. That's why within the three server when the network is really down, so here one, two and three, server the network between this and me is down. We have the majority. Two is bigger than one. So we will tell we are alive. This one as one, the minority is going to tell you I'm gone. So that's why this is actually very essential. We have this like majority and threes for deployment within one data center. And the application will connect to it through so-called router as transparency to access. When one is done, the router will know, okay, this is done, this is gone. It connects to the other server for data. And what if we have some more data center? One, two, three, four. So this is actually the way that we have the replication and connect them together. So in here you see that we put a router in the box like in the DRDC2 in here. So the router is taking care about when the database in here one is done. When one is done, the router knows, okay, one is done, it will connect to the other and to get the data. So it is intelligent to maintain the data stream from the production site to getting the data to the DR as always. And without actually knowing, okay, oh, this is done. I need to reconfigure another channel to pass the data into the DR. So this is again automatic. So look at this. Let's deep dive into a little bit more about what in fact the details about these configurations. So in fact there are so many things that we actually look at. It is text but just to keep the idea. There are things that we call consistency. There are things that we talk about the network, how we make sure we are there interconnect within the data exchange. And there are people, the application connect to me. So in a box we may have two network cards. One network is internal network, one is external. That's why there is so-called IP wide list local address. I will explain it later on the slide. And there is also one thing called network reliability. There are three options right here called expel timeout, auto rejoin, trials, and majority timeout. Those three will tell how to manage the network reliability in the coming slide. And there's also things like how do we take care of the member priority? We call member waiting. So I'm the one server, server two, server three. But how can we actually prioritize? I will always take up the work for ABC. How can I do this? This can be the priority. Oh, I always to do the work for apps. So people write data, always write to me. When I fail, always write to the others. So we have three servers. The third server can be very relaxed. In fact, sometimes when we do jobs, some jobs is very heavy, like reporting, very heavy. We never want this heavy job to actually concurrently to run with the OLTP. So we can put this heavy duty job on the third server, on the third server. Unless we know this is one, two, three, then we can actually run on three servers, the third server. That's why the priority, we can assign priority, which is the member waiting, and we can actually put the workload on the last so called the prioritized server. And there's also how we call this execution. What we do if somebody actually the network is cut and the server is idle there for what, to still work or actually abort and then shut down or actually behave like offline. This is actually in here, we can actually set it abort with only or offline mode. So here I set that custom network. So within the three server, those are the application. The application connect if you know my SQL. It is like port number 3306, for example. But there is actually underlying network. We exchange data. We don't want to expose the data in your network. So we expose this data internal network. So we need to define what this network is. That's what we call local address and also the subnet we call IP wireless. And then to tell, this cluster is talking about interconnect where it talks to. Do not just to use, I mean the default values. The default value is some kind of everywhere. And there is also, I mentioned a post server. So a post server, the red box is the primary. When actually this is actually one server's cut and this server is leaving the group and at the end it's just timeout and shut down. A post server is to shut down. So it is good or it is not good. I believe may not be always good because you see the server is gone and then you may have problem to see should I restart it or is there any other issue why it's shut down. If this actually just offline it's just online and then you can look at the day, the warning and then you can tell what happened, why it's offline.  That's why we have the exit state action. What is the exit state? When this kind of, okay, you're leaving this cluster. What should be the state is going into. And there is also the consistency when we talk about when fade over automatic. But how is this done? So when this actually a server, which is the red one, we call the primary, primary. We write data on the primary, but we read the data on the secondary. So when we write the data on the primary, so data will pass to the secondary, the other toolbox. There are some bad logs, some data to be queuing up, okay, to write to the secondary server. So I finish but I pass the data to you, you have to write back to the database. So what this means when this so-called the apply stage, when one is server, the server is crashed or primary is done and this one is promoted or when it is promoted, somebody will come and then see, I read the data. Oh, when I read the data, the last two pieces, you see the last two pieces data, it was written on the primary, but it is still in the queue. When I read, I may not be able to read the yellow and also the green. I might not be able to read because it hasn't yet applied. So what this means, the data is not the updated data. So how that works, we actually what we do here is the state of data, this actually we want, what we want is when this data applied and then we read it, whenever it's reached, that's why it comes up with the so-called before on primary failover. In the applications we create, we can set the section whenever there is something, okay, we failover, we need to wait, it's automatic. As long as there is default setting that we put it in and before on primary failover, meaning that I need to get the data, okay, with the consistency when I failover. So there is also the setting with the global, one is the section, one is the global. Okay, just put into the global variables, global means the default values. Set it up, the default values, when service startup, AV sections will take over these values, the MySQL router will take this as the default and when it failover to another server, it makes sure it connects to the server with all the data applied and then pass through the connection. So this is actually quite important variables, the before on primary failover. So in here, we do have other options. We have before, after, and also before and after. Where's before? Before means when I have the applications to curate the data. I can curate the data for the actual data, whatever is updated anywhere in this cluster. It has to be applied before I read it. That's why this we can set up the section with this consistency. I need the actual data, the consistent data to be curate, selected. And also when I apply the data, when I write the data, I can set this to after. There's a before, there's also after. I write the data, I will write to server A, server B, and server C, and come back and commit. So this is like synchronous replications. Okay, so MySQL has all these options. It is not so-called async or sync. It's very, very flexible. It's by application. You design what to do. And there's also network reliability. And the network reliability is there's some kind of habits. Are you here? Are you here? Five seconds, you don't reply. Five seconds, you don't reply. I kick you out. Five seconds. Okay, this is what the default. So what that means, five seconds, is it long? Is it short? All depends. Really, all depends. Sometimes there is applications or the network is so interrupt. Maybe even 30 seconds to resume. And it's very often to do that. Then I will say, set this up for this expel timeout, expel timeout. To kick you out, I set it to 30 seconds. That means even there are interruptions with the network. Because within company, our organization may say our network is not as stable as others. We have some kind of interruptions every week. We don't know when, but we don't want disruption to our business. But every week we have this. So what we need to do is we may set this up like 30 seconds, for example. To set this up 30 seconds, then okay, within the 30 seconds it's still hanging around. Because the hobby, I'm still waiting for it. Can this network timeout to be set like one hour? Oh, one hour. That means, oh, are you here? I can wait for every like one hour until I know you are expelled. One hour. That means if you really crash, really, really crash, okay, the system is down for one hour until I know I kick you out. And then, okay, we do work. Continue. So the expel timeout cannot be too long. I have to recognize, okay, maybe two minutes down time is good or 30 seconds. So there is maybe a judgment. What the limit? I believe 30 seconds to two minutes is kind of good values. Maybe. Some people actually 5 seconds, as actually the default. A good network, 5 seconds should be good enough. 5 seconds. So 5 seconds you don't respond, kick you out. Good. But certain network may not be, right? So I believe most likely it has to be less than 20, I mean two minutes. Okay, to make sure that you are, okay, if you are not responsible in two minutes, go away. So this is kind of the expel timeout. And there's also the auto rejoin. Consider when one server is done because of network. So during the weekend, during the weekend, so in fact, in fact during the weekend, you don't care because still two server is running. Okay, one network is offline, two is running but I don't want to come back to office to fix. I need to wait until the Monday to come. So during this like the weekend, I don't want to come back but by some time somebody will fix the network. Okay, if that server is good and intelligent to reconnect by itself, reconnect, then I don't need to do anything. That's what we try. This is like reconnect, we try. So during this time, actually the default is zero. It never we try to rejoin. So if we set it to like 12, 1, 2, 12, it means that every five minutes, every five minutes, it comes to, okay, I come back, I come back every five minutes and try to rejoin. If the network we assume, okay, come back and then back to the state, it's the cluster. 12 means one hour. 12 means one hour. So if we are talking about three days, let's assume the weekend, three days. Then what values do we set this? Three times 24 times, what, right? Times 12, every hour 12. And then that's the value, set it to it. And then three days, you still, the server still keep we try every five minutes. So they are the values, okay? And there is also one called the majority timeout. Again, wow, you are the part of the game, you are responsible for all the data's creation when the transaction is coming to you. At this point, crash. Commit data is trying to ask, are you there? And then are you agree? Are you agree? Okay, do you agree the data? Your network is done. I can listen to you. You cannot listen to the networks from from this, okay, transaction. So this actually the majority is here. Your minority. So what happens to this minority is by default, this value, by default this value is zero, means hang. Means you just hang there. Somebody to look at you, hang there. Okay, zero means hang. Is it good? Somebody to look. And then we to just, oh good, we have to expel timeout after five seconds kick you out. We, okay, you take up the primary. So the other one we will, we have the primary. But you as, also as primary. You have two primary, but this primary is hang. So this is the majority timeout. So what we do, maybe you said, okay, one, two, oh, two minutes. So after two minutes, this hang will come back and then say hours. And when this hours happen, so this actually the data will roll back. And you know, okay, this one, you are actually not coming back. So your minority will turn the state to our state. When turn this our state and then because, oh, error, and then you retry, you will try to see, oh, am I able to, after five minutes, am I good to go back? So this is actually going back to the process. So this thing is a good child to look at how to protect the server and automate the process. How to retry and make sure the network is still unstable or stable and still keep our servers to be reliable. They are very good and important. And in the MySQL class, in the DB cluster, we add new features from time to time. In the just beginning, just in July, we add one more feature called clone. Clone. It is quite easy. And when we have one tool and the third server come in, so it is just an empty database. Nothing. We have data. Always we have data, one server or two server. What it does, clone my data to you. It's just like backup and recovery. So this clone is just easy. And in here, the MySQL shell, we add the instance and recovery method as clone. And the data will be just all data back. All data back. Even the username, all this. By default, your user root is empty password. When I clone my database to you, my user password is yours. I pass to yours. And the empty password is no longer valid on that server. So here, this is kind of the demo. But other things, so this is like automation. This is also performance-wise. How we tackle the database like when data is written back, written back onto the slaves. Here, we have the database as master. Data come here. I pass to you. I pass to you. Data has to go back. We call this SQL Applier. Apply the data back to the database. So we have the algorithm to make sure that we can work in parallel. This is what the parallel type. Default is database. And we can change by clock. Who can run first? Who can run the second? It's by like the timing. By default, who can actually in parallels to run is by database. MySQL, the first line, the first line from Ryan, is talking about database equal to schema. So basically, each database, we can run different threads. So if we have more applications and writing to database DB1, DB2, DB3, then DB1, all these transactions, they are independent of DB2 and DB3. So those actually parallelizations can concurrently execute it by databases, by database. This is the default. But in many cases, we do not run multiple database and then parallelization in this way. In many cases, what MySQL or the application is written is one single database, one single database, or even multiple database, they are, they depend on each others. So what we do is we can change this parallel type to logical clock and then put in a parameter called workers. How many workers do we want to work and to apply the data? Two, three, four, it depends on your iO and also the CPU. You have more, you put in more and data come in more and it actually execute at the same time, at the same time and put it back to the database. So this is how we actually make it, okay, work faster. Logical clock and more threads and the commit order must be preserved, preserved. Okay, so this actually is handled nicely. And in the InnoDB cluster, MySQL, we have this, so automated way of InnoDB cluster. We have some kind of GTID and we need the BIM logs to be in certain format and the criteria. They are BIM log format, checksum, GTID and how the data is actually sitting there in the repository doing the table. And also when we write how we put a hash number and then that's using what kind of algorithm we have to define in here. So here I'm telling you there are a lot of things that make it more reliable and make it run to be better and faster, right? So it's so heavy, we have this automatic MySQL InnoDB clusters to get fade over automatic and to make it work. And there is also router configuration. We have the server, we also have the router. The router, we need to take care how many connections to connect and where we put the data. Okay, the log can be info and on Windows, we can put in the event logs, window events. If you like the windows applications, you know there are places we put the logs on windows. So people will see that the event logs may be a place. And there is also the notifications. Wow, the server, ABC server, we may have server down or someone to switch over because of manual operations. So this is notification. Things changes. Among the server, we need to proactively to notify the router. I have changed. Next time you come to me, talk to this, talk to this, talk to that. So this is proactive. This is so-called use GR notifications and it enables the notifications for what changes we make in the server set. And then it's just applied, and then the router will know and whatever connections come in will know where to connect to. So here's another myth. So somebody will try to put your application on the from drive. From drive. Application on from drive, portable, right? Everything's talking of portable apps. So from drive, most likely from drive is FAT. Am I correct? FAT. So FAT, it has a characteristic. The characteristic is it does not have like the privilege. It's everyone can write and read. And my SQL router, there is a key files, which is the key file it has to be run properly and keep properly. So here is the error. When I run this, there is like, oh, everyone has full access right. Errors. Because there is like password, password and key. It's the key storage in the router. We do not allow this key to be stored in this FAT volume. If you put it there, you'll never be able to start the router. So this is like kind of tricks. So portable app and then you put it there, maybe you'll see issues. So better when you do this, like portable, it's still NTFS if there's a window. Or on Linux, it's EXT2 or 3, doesn't matter, or 4. What is the very common file system on Linux? EXT, EXTFS. Yeah, by default, correct. But on the thumb drive, people don't do it. Still FAT because window uses it. Yes, correct. Yeah, so that's why portable apps, okay, there is kind of tricks. And there's also, do you know what is lock rotation? Lock rotation. On Linux, this is open source. People use a lot of Linux. So the lock has to be maintained. And application has always be active and running. Application always active and running. It always kind of writing to certain files. It's the lock's file. It's being locked.  It runs one month, two months, a year and non-stop. You never be able to clean this up. So we need to find a solution to stop it and then rotate it and clean it up. So lock rotation is the way how we trigger. Usually on Linux, it is using a signal. To signal, so-called a hang-up, H-U-P.  Okay, so this is open source, you are technical. I tell you more detail. Send a signal, kill minus one to the process. It tells the process to close the file and reopen the file. So what we do is, this is actually the tricks. On Linux, you man the lock rotate. Man the lock rotate, you see how you do things and we actually, the router can do this lock rotate at the same time. Work together with lock rotate and the locks can actually be renamed and also can be closed and reopened. So all this, we have the shell. We set the option, we maintain the cluster and they are all be within the shell we call admin API. We have DBA command, we have cluster command, we have all this working nicely and it is command line. Why we have the command line? Because a lot of things we need to integrate this admin to other tools, to other tools and we use some other things to monitor and the graphical GUI or we use others but we still need the admin CLI to maintain the interop with other products. So admin API to get the things how it works. We can set options, we can see options, we can set a specific server options, consistency, fade over and all this can be done within the shell. Only four lines you can create the cluster, four lines of this shell admin API. You can create the cluster up, up, up and then we bring this three into a cluster, four lines of cook and then we can bring them into cluster. It is very easy. Okay, so there is also the way that we see backup recovery. So the backup recovery is the way how we see the efficiency. Oh, we have the a server, b and c. Where do we backup? Sometimes we backup always the very active server, very busy server. No, we don't, we may want the oh the third server which is quite a lot idle and we backup from the very idle and relaxed server. Am I correct? The busy server still keeping to run database on other activity. We will separate the loading on different server so the backup may actually be executed on the lower priority server. So the backup has to be also running fast and we have the writeable server. This is read write, this is read only and this is read only. And when I backup from the read only so this actually the backup will go to the read write server and write the data and telling you already backup and the three server will be consistent and it knows we have already finished the backup. So this information is maintained in the database but this only server cannot be written. So when I backup to this the backup software will automatically it knows this is a cluster and it knows which server can be written. It backup this it will come back all comes to the writeable server and write the data there and it will be transferred back to here. It's all automatic, it's all automatic. So that's why this is like the backup and there is also we talk about the configurations. There are three configurations found in the MySQL world and one is we generally we have the configuration and define all the values, variables. That's the my.cnf or my.ini and there are the other two files. One is the server name, server id, we call the server uuid. It is stored in the auto.cnf, auto.cnf within the data directory and there is also in MySQL 8.0 and now we have the persistency variables. Persistence variables it is stored within the MySQL d-auto.cnf, MySQL d-auto.cnf. So these two files it indicate the actual server identity. Okay so free configuration if I have the data you have the data I have the data. So when I restore to there and then I put up the so-called the three.cnf file and the name they are the same and we just need to make sure the gtid must be the same. So from the backup when we backup using the enterprise all this okay backup from me and I know how to we provision another new instance and then bring it to like in sync within the cluster as one new member I backup the data using enterprise backup and then there is a gtid informations about me about the server gtid means like in Oracle the scn number it knows what actually store within the database what actually I can bring back the data within the scn or we call the gtid. So this information is called metadata gtid metadata this is within the inodb within the enterprise backup when this actually information we cover back to the new member and data is there gtid is there and three configuration is there this is new server with the same set of data as the existing cluster members and they can form the new cluster. Okay so if you want this as the same name as the existing one put it back the three concept if you do you think this actually server a new name okay we move the auto.cnf it will be another name because the auto.cnf is the name uuid you just delete it it will come back oh you are a new member I don't know you because your name is abc my previous name is xyz so if you delete the auto.cnf you got the new name so here this is kind of to tell you so they are the things that we need to protect the three configurations and also the gtid sometimes when I work with customer people always try to use reset master have you heard reset master and reset slave no just the tracking of all this transaction ID oh forget it everybody the same so clear your mind clear your mind you're empty you're empty you're empty so when everybody is empty they are the same right empty database empty database empty database they are the same reset master is just logically to tell you you know nothing you know nothing you know nothing but in the database you store the data so sometimes when I go into I meet customer they tell oh uh quite a few weeks ago because some problems okay you have some problem and you have some problem okay they don't know the problem and then they want to fix the problem how they fix is clear your mind clear your mind clear your mind you know nothing you know nothing I know nothing and then we are all equal now because oh we know nothing then we can bring back you see but in fact you still have the problem internally I still have the problem internally you still have the problem internally when we hit the problem again the problem is still there so superficially on the face surface it is like here we all equal but at the bottom they are not equal so this is kind of many times we go out we see customers just to fix the problem by covering all the facts by removing all the details we set and then you know nothing you know nothing I know nothing so just be aware don't do it because this is down the board down to the bottom it has the data and it has the ABC data it has ABCDE data so when the time somebody updated yee there and then coming back to here I have already yee data then what problem is this duplicate data and cannot apply because we are not the same but you are telling they are the same so this is kind of very popular okay people trying to fix it by covering the facts using resets so this is make sure that we understand correctly what it is doing and people always to back up by with the schedule jobs in on the Linux like cron job and then to back up the data onto a separate folders not I mean the separate volume because backup always grow and then you have never expect this somebody will come and then clean this up so this actually the volume should be untied to the data volume or the data volume should be a stand alone volume for data and people grow the locks grow something else cannot grow into the data volume otherwise the data cannot be written okay better fail but application still running properly okay so I think this is the section about how we can maintain a reliable database and giving you the way always online so questions any questions actually I I have a question yes um right latencies so how does the the various uh configurations uh our strategies affect uh right latencies so for example is it does it block the rights or does it write but then it does not return until until all the data is consistent how how does it work okay thanks for these questions so the latency means that when we have the applications to write so it depends on whether the operation is to write data whether this is like to read data so the question is about to write data to read data okay first to go the other side to read data the latency is about we read on server A server B and server C so they are independent it doesn't require to read from me and then I ask the other data from other servers so it is very fast read and very isolated environment good actually this is a good environment for scale read because all independent three not enough adding four five six and then more users can come to read independently and concurrently so this is read and latency is to read built in it's about i o and memory latency to write write to a server so basically miasko in no db cluster okay can be single primary single write can be multiple writer single writer or multiple writer so let's back to single writer first single writer first so single writer is to write on the one server the one server has to pass data to abc server pass to me pass to the third so the latency is hi i have the data i have the data it requires the acknowledgement that's the latency so this first first it write the data to the server in the memory i mean in the in the memory and then pass the data in the memory to the other server so the latency is still memory not i o at this point not i o this is important and this like we call this certification process and it requires the majority rules it's about latency majority rules means if this is one two three majority is two so when any one of the servers say yes pass and you are ignored why this happened because when this is to write and somebody to tell you okay that means the other one has to say okay otherwise this one just drop off you have problem you just get off so that's why this is the majority rules so when this happened this is latency is fast but to the point us can this be like always like two servers to run because i'm fast you are fast always i respond and this one it's like gone because it never catch up problem happened so no because there is a flow control just look at one individual statement one individual that can be fast but we look at like the overall lifetime of in our operation we cannot lift the other server behind and then we don't care so there is a flow control make sure we do not have too much gap when this actually concurrence we need we do straight tests and this one the latency we will try to hand you wait this one left left behind too much this is flow control so this is another deep dive parameters so to answer you is memory copy memory copy and to write the bin law and relay law concurrently and send the data concurrently to a b c server concurrently so from the latency point is like network and then getting back and then this is independent okay so and also the majority this is fast from single operation it is fast from the overall in and outflow must be the same so i hope you understand this is actually the best option and latency is more than just more than just so-called passing the data latency also talking about the bulk of the data i send a transaction a transaction can be k can be mac if a k one k2k it is small but one mac passing over the stream one mac if we do not trunk k into trunk then things actually in between cannot pass through that's why there is also mechanism to break the big chunk into smaller chunk so there's some other heartbeat in the network can flow through and acknowledgement is like a synchronous to add knowledge to backs to you so this is all built in to the inodb cluster already i hope this answer your question yes thank you very much um any other questions any other questions okay so i think we can take it to break now so but if anyone has any questions please feel free to step up to uh iven and ryan uh during the during the break and ask all the questions you want uh we will be uh back here at 4 p.m sharp for uh more mysql so it will be unleashing the power of no sql using mysql are we fascinating looking forward to looking forward to it thank you very much


Hundreds of protesters clashed ahead of President Joe Biden and Chinese President Xi Jinping's arrival to San Francisco, Biden arrived at San Francisco International Airport and she landed shortly after. The Chinese president was welcomed on the tarmac by Treasury Secretary Janet Yellen, California Governor Gavin Newsom and U.S. Ambassador to China Nicholas Burns, hundreds of onlookers gathered on the leader's motorcade route, some holding signs that read NCCP, the initials of Chinese Communist Party, others held Taiwanese and Tibetan flags, while some waved huge Chinese flags. A sign that read warmly welcome President Xi Jinping was affixed to concrete bollards, dozens of pro-China, and a few anti-China demonstrators had also gathered near the Moscon Center, the venue where many APEC meetings were being held, Biden and Xi have not spoken in a year. Their last meeting was at the Group of 20 summit in Indonesia last fall.


Alright so as human beings we are fascinated with the unknown. Why? Because it's unknown right? And one such unknown that I found that we're really fascinated with is really death. And I know it sounds morbid but more so likely we're talking about what happens after death and what happens just before death. And so I was scrolling through Yahoo on one of my lazy off days like I typically do and I saw this article that piqued my interest about what happens immediately before you pass away. And I thought it was interesting and so I wanted to make a video on it so we're gonna be talking about that let's get into it right now.  Sit down and welcome back to my channel. So as you can see from the title and from my intro I'm gonna be talking about this article that I saw that talks about what happens immediately preceding death. I know crazy right? And so from this article that I was scrolling through it got me thinking because as a trauma PA I see a whole lot of death. Honestly a lot more death than I would like to admit. And if I didn't have to see someone else pass away like in my drama bait I would take that in a heartbeat. But it typically gets me thinking especially when I see young people pass away like what were their last moments on this planet? Like you know what did they see? What did they experience? Because a lot of times they're coming in in a pretty traumatic situation and if that's the last thing they see it's pretty like honestly kind of like a horrific thing to think about. But this article was talking about essentially your life passing before your eyes. Now I know that you guys have heard this I mean it is like propoded a lot in various different movies and different shows. We see people's lives passing before their eyes all the time when they're about to pass away. And with that being said you know it's something that we don't really know if this occurs we can only take their word for it. But in this article there were these scientists that were taking care of a gentleman that came in as a fall. Likely maybe he was on a blood thinner or maybe it was a traumatic fall but nonetheless he felt had a brain bleed that they saw on a CT scan and then proceeded to get an EEG of his brain to see what was going on because he developed epilepsy and he was having these epileptic seizures. Now while he was getting the EEG he passed away. He had a heart attack and passed away and they were able to capture the moments like 30 seconds prior to his brain activity and his heart stopping and kind of 30 seconds after to see exactly what happened. And they saw like this kind of ripple and they were talking about the alpha and gamma waves of the brain and apparently when these two waves interact what happens is it gives you the the processes and memory recollection that you would have as if you were like having a dream or if you were recalling something from memory. I know this is crazy right and so and that been but that being said that it was like okay this man like 30 seconds before he passed away was possibly recalling memory. Now obviously this is one person they can't ask him about it they don't know like what he saw if he saw anything at all but this is the first time that they have like actual proof in a human being that your life actually flashes before your eyes. Now if these are good memories or bad memories they have no idea what it is. They honestly don't even know for sure for sure if you are like recalling like true memories of things that happened in the past. But this is something that they've seen in the the rodent model when they were doing similar tests on rodents and again this is the first time that they were able to capture this in humans. And so I thought this was really interesting especially since this is something I typically deal with on a consistent basis not death but people coming in as falls or traumas and having these head bleeds and these like near-death experiences and it says that this kind of like life you know review typically happens not only prior to death but in near-death experiences. So if this is something that people are experiencing and it's good memories I think it can be definitely comforting to their loved ones that they're not passing like per se like in pain like the last thing that they remember or I can recall is like the good times right. So if you want to see this article or read it for yourself I'm gonna leave it in the description blocks below. I think it's really amazing what science and scientists are able to find and see and do. That is like one of the beauty of healthcare and it's one of the things I really like a lot about the health profession. Definitely keep searching keep researching keep reading you guys. If you have any other like news stories that you saw that you thought was really interesting let me know I'll look at it and see if I can make a video on it but I really want you guys to take a look at this because it is a really interesting read. Thank you guys so much for watching if you have any other comments or questions for me leave them in the comment section below. Don't forget to subscribe and like this video follow me on Instagram and it on the PA and on Instagram and get that's the University. Thank you guys so much for watching I will talk to you guys next time. Bye!


First of all, thank you for coming. I will be honest with you, I wouldn't have been surprised, at least, if the room would be empty. I mean, it's security nightmares, I mean, we're talking about one of the two major events, and I'm really, really flattered by the attention. So, I see we do have an issue there, cause, nope, boom, boom, boom, boom, that's screen number eight, sorry. You know how stuff works, don't you? And of course, I am in the wrong folder. So you will see me doing some command line fill, boom, boom, oh, come on, three, two, one, see it, three, presentation. So this is the main part where I explain to you how you start a presentation over the command line. And here we are. And this thing's great. I think we do have to solve that problem here. I do have to, I'm sorry, okay, that's how things work, boom, boom, boom, three, presentation. So yeah, as you have imagined, it's about making your own, tell us, I will talk, I will bravel along, because I'm here, that's kind of, yeah, do you know, I'm sorry, I just screwed up, totally. Don't worry about it. I think you're not live. So he told me not to worry about it.  It's the last day of Congress. It's the last talk. We had four days of not much sleep, probably. Yeah, tell me more about that. And we are all hackers, so we love terminals. And why not just look at them for a few minutes? So yeah, just appreciate the beautiness of green fonts on black backgrounds. Oh, yeah, yeah.  And I'm not, I'm not especially the, I'm just, I'm just saying I've only happened, I've only seen that happen with Linux machines, right? So not that that's any reason, but I see stuff happening on his monitor. So maybe we're close. Let's set the duration to 45 minutes, shall we? Yeah, don't worry about it. Here we go. Nice. No, why? Yeah. Huh? Just go with it. No, I can't. It's, it's, yeah, no, that's not the problem. The problem is that the other half is on his laptop monitor. Okay. Okay. So now, now we're gonna do it. We're gonna do it. Yeah, just wait. So here. Here we are.  So I don't know. You probably have time. So all right, we've got something here and we're left to go. Nice. That's, that's, that's always the thing. If you, I really, I looked up what tool should I use, there are a lot of ones you can buy. And yeah, I, this one is open source and of course I love open source. So I use that and never with the second monitor because of course I never thought about that. So yes, it's about amateur telescopic. First of all, what I often hear when I tell some, I mean, I'm at the People's Observatory of Munich. I did also some research in astronomy and so I'm involved and I do, I show people the observatory. I explain them how telescopes work and when I tell them, look, you can make a telescope yourself. Yeah, of course. It's an optical precision instrument. You have to, you have to have expensive machinery. You have to know a lot about optics and stuff like that. Well, yeah, no. Because you need the expensive machinery if you are going to do it with a machine.  That sounds wrong. If you, if you're going to do it by hand and we're talking about telescopes roughly in the range up to a meter, meter diameter. Imagine that. That's a huge telescope. That's a big-ass telescope. You can do it by hand. It's a lot of work, but you can do it with the mere attribute of a human being not being able to repeat emotion again and again the same way, the exact same way, especially if you tell the people, look, embrace the randomness. You can do it. You can make a telescope that beats manufactured telescopes you can buy. And you can pay a lot of money for it. So here, that's a short outline. So if you have more questions, write me an email, Twitter, whatever. Come to me personally, although we don't have that much time. We can, I can talk to you about anything you want. I can tell you where you can get those, where you can get the stuff. And if you are interested, hit me up and I will, I will share all the knowledge with you because, again, the knowledge I got, I'm not the best guy there is. I happen to live in the same city with the best guy there is in Germany. And if he's watching, and I'm sure he's watching, thank you, Stathis, for showing me that and for making it possible that I can make my own telescopes. I haven't finished a single one yet because I always rework stuff three or four times, including those slides here. So why do I need a telescope? I mean, I can go out in the dark. Dark isn't a very important part of it. Astronomy works better if you can see the stars. Except radio astronomy, but we're not talking that here. We're talking optical astronomy. Why would I need that? I mean, I do have an eye. I can see the stars. I can see the Milky Way. It's an impressive view. And I know people who, because it was such a nice view, it was a clear night. It was lovely. They went outside. They carried the telescope. They assembled their telescope on site and thought, well, screw it. I'm going to lie down on the grass and have a look at the sky and enjoy it. That's it. That's about amateur astronomy. You love to do it. And well, if that works for you, go for it. If you make a telescope, don't let anyone tell you, oh, that doesn't work. If you know it works for you, do it. It's the most important thing. You can make it like you want. So here are some incentives. First of all, with a telescope, you can have a look at galaxies, like that one. This one is also from a ground-based telescope. But as you can see, those guys, well, they do it for a living. These are the European Southern Observatory. So you won't see that in the telescope. But you can see a faint blob. You will see that region here. If you don't like that, well, then I have bad news for you. There are better objects, like Albirio here. This is a double star. And this is a star. You can see it with a naked eye. But in the telescope, it resolves to two stars orbiting each other. You don't see the orbiting, obviously. And the one is blue, the one's red. So here you can see astronomy.  Yeah, wow. If you see it in a telescope, then it's something completely different. The more you know, the more this experience on the eyepiece is enhanced. And planets. OK, that's Pluto, sorry, old habits die hard. Planets. This one is actually what you would, of course, not that detailed, because there's still an atmosphere in between. And those are probably some thousand pictures. No, that's Hubble screw that. So you can get those quality pictures, similar quality pictures with an amateur telescope, but you need to take a video. You cut out parts which are good, which you like. There's software for that, of course. And you end up stacking, like, two or three thousand pictures. And then you get good quality. It will be, if you have a look at it yourself, it will be a bit blurrier. But you will definitely see the stripes and the big red spot. Fun fact, this big red spot is twice the size of the Earth. So big is quite a good name for it, I think. Yeah, let's go back. So you need light. You need to cut.  It doesn't make very visible, you don't see, but it can make light and regions visible. You don't see because it collects light. It bundles up the light. So how do you do that? Well, there is the classical method, as you saw, a lens. Light comes in, focus comes out. You can't explain that. Well, actually, we can. But that's how this thing works. Everybody who wears glasses, who has used a binocular, or whatever you do, that's the main principle. And that's what most people imagine when they think about a telescope. Then again, mirrors. Mirrors have one huge advantage. You have to use only one surface. So they're cheaper manufacturing. You can support them from the back. They're easier to build. So nowadays, mirrors are the way to go. Doesn't matter how big. If you make a 6-inch telescope or a 8-meter telescope, like the VLT is, or a 40-meter telescope, like the ELT is going to be, let's see that. I would love to see that, 40-meter telescope. I mean, that's astronomy porn. I mean, we're talking hot stuff here. So what this telescope does is basically you have one main component. That's a Newton, as you can see. And by the curvature of the mirror, of the main mirror, let's call it M1 here. Mirror 1, mirror 2. You can imagine how this works. You basically band the light in one direction.  So that's how it works, the basic concept. But now, since I mentioned basics, let's go to the basics. This are some circles, some colored circles. What they represent is here. Imagine that being 7 millimeters. That's the eye opening of a healthy young adult at extreme low light conditions. So that's the maximum your eye can open up. And if you go above 30, I have bad news for you. That's not going to be 7 millimeters. It's going to decrease with age. People of the age of 60, 70, they're talking 5 millimeters. So you can see, well, OK, that's surprisingly big. If you actually, I did that, I drawed it and draw it actually with millimeters and scale it down to fit in the slide, and whoa, that's big. Yes, it is surprisingly big, but it's bigger. The circle next to that represents a 50 millimeter optical, a 50 millimeter aperture. So this is the cheap telescope you're going to buy your kid for 100 euros. Please don't do that.  So the kids end up being frustrated and driven away from astronomy just because of that. And binoculars are the same diameter. So you can buy for 100 euros really, really decent binoculars with two times this aperture and have a look at the sky. It's not expensive hobby. It's really, really good. What you can see, and people put aside the big telescopes and use a binoculars, every telescope has its own sky. You see different things, different magnifications. And I mean, it's really, really, you can start small. That's what I want to say here. Then we have a 140 millimeter. That's a typical starter telescope. And this here, this is no moon. This is a one meter mirror. It doesn't fit in the slide. So as you can see, most of you already know it. But the surface area grows exponential. So you increase the diameter by two. And as you can see here, the surface goes up by four. So in the end, you collect more and more light. And light is extremely important here because you're trying to get the last photon out of that object. Oh, the last photon that hits Earth. Another thing is that with diameter, you also increase the resolution. So here, that's the so-called baseline. Actually, to increase the resolution, you don't need that part. That part simply collects light. You could just use the part on the left edge and on the right edge. And you would have that increased angular resolution. And in fact, we're doing that. It's called interferometric astronomy. It works great with radio telescopes. But with optical telescopes, they're right about bringing it to functionality.  A bumpy road, sorry. Sorry, I'm totally on caffeine. And you know how it is. Big audience. You get bright light in your eyes and you barely can see the people down there. And that's how it goes. So it goes, it goes inverse proportional. So again, the types of telescopes, how it works. Here, the light goes in from the front. And because it's a mirror and it's reflected, you do have to have that part here, the secondary mirror, which goes up. And here, you have a typical single lens telescope. You can see you have color errors here, but that's not the point. The point is what I want to make is here, you have two surfaces, here you have one. One surface doesn't have to comply with anything. You can have one surface, you can make it work. And at the moment it works, it works. Here, you have to make two surfaces work with each other. And that's much, much harder. Because if you happen to make it wrong, it can totally go south. If those two are not centered properly, the whole optical capabilities of the telescope go really, really bad. So yeah, now to the main part, making the telescope, actually doing it. First of all, I will talk about the optics. This is the part which is most complicated. I'd say complicated is the wrong word. Less people are familiar with optics than they are with making words, aligning words so that something works. So that's the new part for most of you, I guess. I happen to know that at least one person in the audience is already thinking about making a telescope, so he maybe knows more about that. But it's not complicated, it's not hard. Why would you make your own telescope? I skipped a slide. Well, basically, because you are flexible, you can make it the way you want. If you want to make a telescope that's pink, you can make a telescope that's pink. If you want to make a telescope that's rubbish, you can make a telescope that's rubbish. You can make it however you like. And you can also include rocket launchers, which was suggested by somebody. But I wouldn't recommend most other astronomers don't like a rocket launcher being on your telescope and destroying their hard work. The quality, again, if you want to make it, you can make it as good as you want. You can go through N plus 1 iterations and still add another one. You don't care. OK, you care because at one point you want to use it, actually, and make something with it. But that's where I'm stuck. I'm making the iterations. I started writing my mirror from scratch two times now. So you can adjust that part. If you need a telescope that's only going to work for infrared light because you want to make an infrared transmission path, go for it. You don't need to invest that much time in it. You just need to polish it roughly, and it works. You don't have that high specs, as you have with optical light. The price, of course, although a small disclaimer here. If you're going to make a telescope 10-inch big and you want to save money, don't do it. You can buy really decent telescopes nowadays, with up to 16-inch. And you would still save money. I'm talking about raw costs here, not the time invested. If you calculate that, it goes through the roof. I'm talking about cash. You take your hand and put on the counter. You will save money up to 16-inch. But make a small telescope, one that you would like to use, of course, to gain the experience, to see how it is, how it works, where the problems are, and then go big. If you go really big, if you go above 18, 20, 24, 30, to 3 inches, 40 inches, the sky's the limit here. People are running amateur telescopes with one meter diameter. That's insane. If a guy arrives at the site with a trailer and he tells you, yeah, that thing is full with a telescope, with one single telescope. And you have to climb up a ladder 2 and 1 half meters to get to the eyepiece. You know what I'm talking about? Why I say it's insane? It's crazy. But then again, we are at the Hacker Congress between the holidays. I guess we are crazy, too. And, of course, availability. Telescopes above 18-inch, light construction, light that you can carry it with one person. That's considered light there. They're not that abundant. They are some small manufacturers. And you order it today. You will have it at the 33rd C3, maybe. So we're talking two years of delivery time. And in that time, of course, you will be able to make your own telescope. And most importantly, because you freaking can.   You had to build it yourself. But nowadays, in Germany, at least, you pay 500, 700 euros. And you get the decent one, not the best one. And still, it has issues. But you get a good one. But many people still do it. They're all 3D printers. I mean, there's Linux from scratch. I think I still don't understand. But maybe that's my lack of understanding there. But still, people do things themselves. And that's always the reason. Because I want it better. I want it now. I want it. I want it. However I want. And that's here. So the shopping list. So you say, cool. I want to do that. And you start. And you say, well, I want to go to the hardware store and get the stuff. So what you need is a piece of glass, a small disclaimer here. You need special glass. Not always. If you make small telescopes, I know a guy who made his two really small telescopes, four inch, with standard window glass, which is a nightmare if you do it. But it's OK, I guess, for that size. And it's cheap. It's definitely cheap. He paid exactly nothing for it. I mean, we're talking four inch here. That's the size.  I mean, from the scrap. It's like, yeah, you can get that. Nobody cares about that size of glass. Then you need a tool. That tool can be another piece of glass. It can be granite. It can be ceramics. It can be a composite construction that you take two plates or two bathroom tiles. You glue them together. You put them together with some cement or some clay or whatever you find. And seal it around. That's the important part. If you want to start it, Google. Google, Google, Google, or ask me. Or you can write me. I can tell you where you will find your tips and where you find your materials. Because many, many details are omitted here. Like, 99% of the details are omitted here. Some sand, silicon carbide, actually. But that's, yeah, we call it a little. You take two pieces of glass, throw a bit of sand in it, and then you have a telescope. That's how one guy put it once when we discussed it at an astronomy meeting. And polishing agent, that's most of the time, that's not aluminum oxide. Cerroxide, really interesting chemistry going on there. And nobody really knowing why. If somebody in the audience, and that's me asking somebody for help, knows how seroxide works, how it polishes glass, come up. You're going to get a mate. Really, I really had a hard time to research that. And pitch, like the black thing pitch, not the tone one. So here we have our, that's the mirror, that's the tool. Here I illustrated two pieces of glass because I was lazy, pure laziness here. What you do is you have those two mirrors in between. There's the sand, those pieces of glass. Here's the sand, the abrasive. And here you put pressure on it. So what happens? In the center of the top part, you have higher pressure. And on the edge of the bottom part, you have increased pressure. So hands up. And I want you to participate on that. What will happen with the top part? Yes? You wrote the middle. You wrote the middle.  Oh, do you remember the slide from back there, where we had that concave mirror? Well, that's what happens. You get the curvature. And if you do that chaotically, enough. So you turn the two parts in opposite directions randomly. Like you make, actually, I wanted to make a small demonstration here today. But guess where that demonstration is exactly at home? Well, it's absolute with some perfect use. So you rotate it. You move it along. You make different lines. You make overall a chaotic movement. And you end up with a sphere. So what you do then is you measure how deep you are. And you know the shape of the sphere you have. And if you get to a point where it is the shape you want it, you refine it. First of all, with silicon carbide, you start with a granule size of 60. Oh, by the way, silicon carbide, everybody knows it. It's the stuffed gluten sandpaper.  And then you go to aluminum oxide. That's a really fun fact. So I was traveling around in Munich taking the metro. And well, as chance will have it, I forgot my wallet at home. In the wallet, it was my student ticket. So basically, I got checked. Of course, when you forget it at home, they check you. They ask you, where's your ticket? Never mind. So sometimes it happens that the police is present. So imagine a police officer. Oh, tell me what's in the backpack. They're actually allowed to do that. What's in the backpack? Yeah, I just got my mirror. And there is also some polishing agents, some silicon carbide, some aluminum oxide. And whoever knows what color aluminum oxide is, pure white. And then imagine that being a powder with the size of nine micrometers. That guy started asking questions. Thank God they had like a rapid test. And I told him, look, guys, you see, that's a set. That's the 80 granule size of silicon carbide. That's why it's black. It's silicon. And I explained. And then they believed me. But still, it got complicated. Yeah. Sorry, I didn't understand. I really honestly don't hear what you're saying. Is the mic on? I just said you can be very lucky that I didn't ask you for a bioassay, that you didn't have to try out the powder and put it into your body somewhere. Actually, yes. There's some research coming up about what aluminum does to your body. It basically screws up everything. But so don't inhale it. That's a bad idea. OK?  You refine the surface. Starting with the 32 micrometer aluminum oxide, you can already see. If you look at a flat angle on the mirror, you can see it starts reflecting. That's where you get, oh, God, yes, yes, yes. I'm closer to having a mirror. No, you're not. Then the work comes in. This guy here who's putting the polishing angel on, that's the corporate holder of Stathis Cafales. That's the guy who's like the guru in Germany, in my eyes, my opinion. But he knows a lot about grinding mirrors. And yeah, I know he's watching. So yeah, I know he's probably going red right now, but I don't care about that. So what you need is cerium oxide and pitch. That black thing, you know why they call it pitch black? Well, there you see it. And this yellowish powder, which was also a funny thing, they wanted to test it out too. You dissolve it in water and you put it on the pitch. And you don't put a lot in it. That here is really, really, you see how thin it is. You don't put a lot in it. But still, the cerium oxide kind of interacts chemically with the glass. Then again, it bets itself in the pitch and kind of like millions and millions of razors cuts the glass away and polishes it away and kind of smears it. Also, there is some theory. I found a paper by some Chinese researchers, which I dare not pull. I don't know a lot about that stuff. But I don't actually believe it that there is also some thermal process going on, hitting the glass up and smearing it away. I honestly have no idea. Those Chinese guys who wrote the paper, I don't believe, have more credibility than me in that matter. So then you need to test it. All the process is very terrestrial.  First of all, you want to find out how deep is a mirror. What is the shape of my sphere? That's how you do it. You take a ruler and measure that distance. Fairly easy, isn't it? No high-tech involved here. The more high-techy way, high-techy, whatever, high-tech in terms of the 17th century, is you take a torch. You make the mirror wet. You take a torch, and you look where the reflection goes. And if you hit the right spot, you will know that if you hit it, believe me, you measure that distance, and you have the radius of the sphere that the surface is an element of. Sounds complicated, it isn't. It's really basic geometry, because a spherical mirror will reflect everything that comes from the center back to the center. That's what we use to make the fine-testing with the focal testing. Leon Foucault, probably most people know him of the Foucault pendulum, but this is also an ingenious method of making high-precision measurements on mirrors and reflecting surfaces in general with minimum monetary involvement. You are talking, to make it for a co-tester, we are talking, if you are going to go fancy, like really fancy, we're talking 50 euros here. You can make it actually for free if you go to a scrapyard or something like that. It's really, you can make it really cheap, and it's really precise. It's surprisingly precise. And then again, interferometry, that's like the more techy way. I won't eliminate interferometry here. I could make a talk on interferometry alone or interferometrical testing of mirrors, because you have to take into account so many effects that I'd simply say that's nothing for the beginner, but if you go, there's a lot of information on that to read up. So Google it, you will be more than happy with information you will get there. So here we have a for-co-tester. On the bottom, you see the light source, shining onto a mirror, projecting the light on your test subject. And here you have an edge, a knife edge. That's why it's called also for-co-knife edge testing. And here what you can see illuminated is, so basically what's the thought behind this? Here, so here we are roughly in the center of the mirror. We are talking here the dimensions are scaled down in order, that's a Wikipedia picture, in order for it to be able to understand it. But that size, if compared to human eye, that mirror would be there. That would be a typical focal distance for that one. So here we are roughly in the center. So what you do is you know, OK, if I project something from the center on the mirror, it goes back to the center on a single point. So if I put a knife edge there, a really, really sharp edge which blocks or which is binary blocks or allows light to pass through, if I had a perfect sphere, a perfect setup, theoretically, I would get, I would see the mirror or the test subject illuminated. And then it goes black as I move the edge back and forth. Well, reality kicks in. And you get deviations from the sphere. So here that's more or less a good sphere. You can see, you can already see, here there is a, you have kind of something funny going on here on the edge. Here something, there is a kind of a mountain in the center. Here a smaller mountain combined with a ruined edge, I'd say. Here you see some shadings. Here you see a pit in the middle. And again, this edge, this is a typical era beginner's make. Nothing you can't correct. But yeah, so this is what you would see. And you see here, these deviations from the sphere are, we're talking about maybe, here it's huge, we're talking about 200 nanometers. Nanometers, excuse me, 20 wavelengths, sorry. 20, so lambda 20, I'm sorry, yeah. So this is 20 wavelengths. And as a matter of what you would use as a wavelength, typically white light, so you would use, that's 20 times 400 nanometers. That's a deviation here. We're talking about precise testing. Actually, I don't know if I am. I do have that picture where you have that photo test and somebody puts a hand in the beam. You can actually see the thermal turbulence of the hand. So you can imagine what the resolution here is. It's really, really good. And yeah, interferometers, this is basically for you to have something to Google. Those are interferometers which work, which amateurs have built, common path interferometers. They are not that precise, but they have an advantage in construction. So that's basically for you, if you want to look it up, that's what you would Google for bathroom interferometer, point diffraction interferometer at the fissile, which is also point diffraction interferometer, but with a special setup. Again, I could go on. I didn't exactly lie to you, but I didn't tell the whole truth. This sphere does not provide a perfect image. If you have light coming from infinity, here we have an illustration. If you have light coming from infinity, here parallel beams, always helps shaking up batteries. So here you see that's the focal region. That's called spherical aberration. You have it always with spherical optical elements. They kind of have a hard time into focusing light from infinity onto one point. And correcting this is fairly easy. You just take your sphere. This is a bit exaggerated, but you take your sphere and make a little dimple in the middle, and you end up with a parabola. And a parabola focuses all the light on one point, coming from infinity. Again, this is really, really exaggerated. Car lights use that inverse path. You have the light bulb here, and you get a parallel path there. Parabolic antennas, guess where they got the name from? So testing that is kind of a bigger challenge, because you don't test the whole mirror as a whole. And you only know how to test spheres. So what we do is we cover up some areas there. It's called a mask. You have black paper, and you cut holes in it. So what you do is you approximate that parabola with a lot, and lots, and lots, depending on how many you want. For a small mirror, three regions. For a big one, you would use up to eight, up to 10, 12. I've seen one with 14. That's just insane. So you approximate the mirror with zones. You assume that you have a steady curve. You don't make some funny stuff between the regions. So what you do is you measure a lot of spheres, and if the relations of the spheres to each other is correct, everything works fine. There is also software where you can calculate what that relation has to be, which fits everything and stuff like that. You can do that in an Excel sheet or LibreOffice calc sheet. Whatever you want, you can do that. There's a lot of software. And if you search for co-interferometry, you will stumble upon those pieces of software. Most of it runs on windows, but wine works just fine. So this is the grinding part. Making the mirror. For a 8-inch 200 millimeter mirror, we would calculate, if you are good, 90 hours of grinding, polishing and everything included and testing. If you are average, we're talking rather about 130 to 150 hours. The biggest part is building the telescope. First of all, you have to decide, what do I want? Do I want a telescope which I want to perfectly possible with an 8-inch to take it with you on the airplane? Hand luggage. I don't know if the TSA likes it because they don't know. But I know people who take their telescope on the plane as hand luggage. Maybe you want to, I had a problem. I needed public transport. I didn't have a car recently. So I needed to carry that telescope with me on public transport. So I bought one, blame on me. But yeah, I bought a small telescope. I have that in my backpack. I have a tripod in my hand. And the eyepiece is on the other hand. And I just can't go ahead. People can take me easily with them in the car or whatever. So it's not easy for them to say no and just say, OK, I don't want to. I don't have room or whatever. It was really, really compact. And people are even going for a hike with their telescope. So we are talking about really, really light, lightweight, and compact stuff here. But if you want to observe from your backyard, there's no point in investing all the time and the money and the complicated constructions and the many failures or whatever. You just build a telescope that works and you don't care how heavy it is. You put a plastic sock on it and it's protected from rain and everything. It's just there. If you want to take pictures with it, there are different demands. So you have to decide what do I want here? What do I want to build? So let's start with what are the main factors? I mentioned transportability, handling. The best telescope is of no use if you can't use it. That's a tautology anyway. And you want it to be rigid. You don't want to invest tons of hours in your optics and making everything perfect and then everything being sloppy and shaking around. Because that's the main reason. Do you remember those cheap telescopes I told you about? Don't buy two cheap telescopes for kids because they have sloppy mechanics and they are no fun to use. And if it's no fun to use, you won't use it. And if you want to use it, then don't start in the first place. So those are really important factors. And especially the transportability is a thing. Also, your budget. If you have no budget and if you have no car, there's no point in making a one-meter telescope. We are talking about 5,000 euros only for the mirror. And if you are not careful, and that guy in the stream watching right now, he knows what I'm talking about. He made an eight... You can have... Maybe you ruined 400 euros worth of glass. He was nearly done. He was nearly done. He was doing his final tests. He had his telescope, he had his mirror on the bench. And his kids were in the house. He was eager to finish it. One of the kids opened the door. A wind went through the house, kicked the mirror off the stand and you had three really, really well polished shards. Yep. That hurts. Another guy, Mr... The stuffiest guy I've gotten those pictures from. Thanks for that, by the way. In order to avoid that, he put his foot under the mirror to catch it. He had a broken foot. The mirror was okay. He said it was worth it. Imagine. Imagine. So, yes, be careful with it and calculate... Failure shouldn't ruin your budget planning for the next holiday. So, basically, one thing you have also to decide is how do I want to mount it. Here, this is an alt-azimuth mount. Shortened up alt-az. So you see, it's easy. Up and down, left, right. You have two axes perpendicular or parallel to gravity. Perfectly fine. Engineering, no challenge. Here, we have a German mount. The reason you would do that is you want to take pictures. So, the earth axis is tilted. And what they do here is you have one axis parallel to the earth axis and you counteract the movement of the earth, of the stars, relative to the earth, of course, and you just move your telescope along. So, you just have to worry about one axis being guided properly. That's a huge advantage, trust me on that. You have one... Even there are clockwork like this clockwork. Old Russian clockwork mounts which work marvelously. They are great. The only problem is once you winded them up, again, police, so you are on tenorify, you have your clockwork, oh, it's a great night. Tomorrow I'm flying, I don't care, I want to take pictures. So, you wind it up. You wind it up a bit too much because you want it a bit further than you think you will need. And then on the next day, somebody checks the bags, the luggage, and here's it coming from back. Yep, explaining. Oh, actually, you see what shape this thing has? One amateur astronomer, she's a really great person, great human, and she was on top of a mountain. And she was setting up her telescope, was observing, and nearby there is a military area. One of the residents saw somebody putting a silhouette that looked like that on top of a mountain. There is, in German, there is a... If you observe, you want everything to stay dark because adaption to darkness is something that breaks really easily and it's about half an hour to rebuild. So, you avoid light. And there is the term Weißlichtsau, which means white light pig. So, she was there on the telescope, somebody, they sneaked up on her. We're talking about special ops, here, spec ops. Sneaking up to her, lighting the whole area, and she just saying, Weißlichtsau. And then looking up and seeing guns pointed at her and people screaming, go away from the rocket launcher. So, you see astronomy is a really, really peaceful hobby, but yet again, that doesn't happen all the time. So, I don't want to scare you off here, but I just want to loosen you up. So, that's how you would build an altars mouth. That's a typical example.  The focuser is something you can build it yourself and especially nowadays with 3D printers, you can easily print one for yourself, but you need high precision and honestly, they don't cost a lot. If you get a really, really fancy one, you're paying 300 euros. But we are talking about really, really fancy stuff. Okay, if you go really big, then it goes really, really expensive. Actually, how much time do I have? Five minutes?  I mean, I was told that, okay, I have five minutes, I'm sorry for that. So, what you can make a trust of, that's called a Dobsonian. So, here is a full tube Dobsonian, that's like kind of the stuff you can buy. This one is really, really heavy. We're talking about, you can separate the pieces here and carry them around because you can't carry that in the hole. I think it's a 14 inch and yeah, that's a full tube one. Then a trust Dobson. This one is a 32 inch Dobson. 32, yes. So basically what I'm telling you here, this one here, the Finder is also a Newtonian telescope. It's just four and a half inches, but that's the Finder. This mirror here, the Signer mirror, has that size. So, we're talking about a really decent one and you can see really nice things with it. Oh no, I stand corrected, 28 inch, sorry. And again, a trust Dobson, that's a classical design with eight rods, by the way. And here, this one is meant for photography. So, this one has to be really, really sturdy. You don't want your camera, which can be quite heavy here in the front, to move relative to your main mirror. That's really, really bad karma. You don't want to do that. Your picture is going to be ruined.  So, really, you want it to be as steady as possible. So, that's why it's made like that with a huge diameter in the middle and going smaller, going thin outside, because it's also mainly supported in the middle. So, here you have a three rod design, a two rod design. This one is really, really, really compact. You can, the rods are separated. You see this here? Those are base strengths. This thing is set up and you can play music with it. Not a good one, but you can play music.  So, this one is a compromise going totally for transportability. You lose light if you do that, because you have the strings going in the optical path. You have this huge thing here, so you want to have it really light. You're losing light, but you want it to carry it to carry it with you. And I happen to know that Stathiff has made a, with his motorcycle, I took with that. So, yeah, everything possible. So, the top part called, I have to speed up a bit. So, if you don't understand something, please forgive me on that. So, the hat, the top part has two main components which you want to support thoroughly. Here, the secondary mirror, that's the shiny thing there. Guess what? And the focuser, that's one of the fans, one that costs 200 euros. And you want that hat to be as light as possible because you are away from the center of mass and you want it to be stable. You see engineering problems coming up. Everybody does. And solving this problem seems impossible, but it's really, really well, they're really, really good solutions. So, here you see trusses here on the supports. And, yeah, here, another solution on that. And, yeah, so, you can't solve it. People have actually made hats, made secondary mirror supports with guitar strings. So, everything's possible here. Two minutes? Over? It's two minutes. It's maybe five. I'm speeding up here. Sorry, I, sorry. And here you have the mirror box which is basically quite easy. You have this structure here which supports the mirror. Here, there would be silicon pads if it's done. And everything moveable, easily moveable, that everything can be, can align in such a way that there is no torque on the main mirror. You don't want that. You really don't want that. It ruins your image for no particular reason. So, you don't want to do that. So, here again, the altitude wheels attach to the box and the rods here. And you basically, and all that goes on the rocker box which is basically Teflon grinding on top of Ebony Star. Ebony Star is a top counter cover, a kitchen counter, a kitchen top counter cover. So, it's easily accessible. They don't produce anymore. There are alternatives. But yeah, so that's how you would do everything. I want to thank those guys, Stathis, Martin, Tassilo, and the People's Observatory. And I want this talk, I want to dedicate this talk to John Dobson without whom this Dobson design would not have been possible. He died earlier this year, in January last year. This year, last year then. So, he died earlier this year. And yeah, was a huge loss, definitely, for the community. And that guy was the one that made democratic, that democratized astronomy for everybody, the sidewalk astronomy. And yeah, some software here. Just Google it up, open source, everything. Do download it, modify it, improve it. And some links where, yeah, Cloudy Knights, that's an English forum. Everything is organized with forums in the sector. AstroDref and AstronomyDee are sites that are German. So, everything happens in German. And yeah, can we arrange five minutes for a Q&A? Yeah, I think that's possible. Thank you. Sure, yeah. So, if anyone has questions, just come to one of the four microphones and we'll just go ahead with microphone three. Hi, I was curious, hello.  There is some science done, but it's mainly variable stars and asteroids and planetoids, stuff like that. Because the problem with, you could possibly calculate or measure redshifts, but the matter with that is you need high, for redshift calculation, you need high resolution spectrometers and those are expensive and they are expensive for a reason, so they're really, really hard to make. So, yeah, to calculate redshift is kind of a hard thing and you can only, spectrometers need a lot of light, so you can only do that on bright objects and all the bright objects have already been measured, they're the hell measured out of them. So, you can do that, but you can contribute in science with that. Main contributions of amateurs are, again, as I told you, small planetoids and variable stars, but there's also one site called galaxyzoo.com where you have pictures of galaxies and you can sit there on your PC and it works great if you have to wait on somebody, you can say, okay, that's a spiral galaxy type and so on. So, you can help classify galaxies there. So, you're welcome. Yes, please, mic number two. Hello. Yes. If you're using purely glass for the mirror without the shiny surface known to the bottom, isn't there a big loss of light? Yes, yes, yes it is. You have to cover it up. I completely forgot that in my talk and I forgot that completely. Thank you for putting that out. You have to send it somewhere. You need a vacuum chamber to aluminize it and to put also a cover material on top. Come on. Silicon oxide so that you have that sealed, but you can do it also at home. There's a chemical reaction which drops out elemental silver and you can cover that in silver, but it produces hydrogen and hydrogen is kind of an explosive matter. So, you want to be careful with that. Mic number three. I just wanted to mention you mentioned Dobson at the end. So, I just wanted to mention something. The funny thing with Dobson is he started astronomy because he was converting to Hinduism and the funny thing is Hinduism has, where we all know Christian creation, clear to listen. Yeah. The funny with the 7,000 years old, the problem with Hindus is they have to accept different problems. They have an universe that is billions, billions of years old. And so, one of the reasons he tried this one was to get people for a steady state universe model. And so, I think it's something to show that, well, be a little bit tolerant to religious people.  I happen to have seen an interview where he said that this big bang theory thing is complete. And we're not talking of the show here. Yeah, that's bogus. He said that. True, but he made a huge contribution to science. I just wanted to say because we had a problem with some... Because we are running tight on schedule, maybe you're... Thank you for sharing that with us, yeah. Yeah, I have a question. You said you cannot use regular glass, so what kind of glass are you supposed to buy? You want to use glass that has a... That doesn't expand as much with thermal differences. Because you want your mirror to cool down smoothly, so you don't have bumps and ridges building up just because the glass is expanding or cooling down. Because you have to imagine you are carrying this telescope from a 20-degree Celsius perfect environment to, if you are not lucky, to a minus 10-degree environment, and even with that special glass, you need to wait some time until the mirror has cooled down enough that you can observe. It's really... That's the whole thing. And if you make small telescopes, you can use thin sheets of glass, normal floating glass for windows, and then again, thin sheets cool down easily and you have no problem at all. So that's the only reason. What is called the glass you use? It's called BK7, it's called Pyrex. There are many... It's basically, most of the time, it's floating glass, so there are many trademarks on it. But the way I would buy glass for that is hit up a guy who sells glass for those purposes. There are many and it's not really that expensive. Okay, so I think that was it with the questions. Looks like it. Yeah, thank you again.