Hi, 8th June 2001 12:15 hrs chennai  This topic will cover how
to Diagnose and solve the Row chaining and Row migration in a
Block.  What is Row Chaining ? The row is too large to fit into
an EMPTY data block.In this Oracle stores the DATA for the row
in a CHAIN of one or more Data BLOCKS.  CHAINING occurs when row
is INSERTED or UPDATED  Row chaining can happen for very large
rows such as rows that contain LOB.Row chaining in such cases is
Unavoidable.  Graphical representation:    What is Row
Migration?  An UPDATE statement increases the amount of DATA in
a ROW so that the Row NO LONGER FITS in to its DATA BLOCK.
Oracle tries to find another Blockwith enough free space to hold
the entire row.If such block is available Oracle moves the
entire ROW to the NEW BLOCK.Oracle keeps the original Row piece
of a Migrated row row to POINT to the NEW BLOCK containing the
actual row.The ROWID of the MIGRATED rows does not
change.INDEXES are not updated and they point to the ORIGINAL
row LOCATION.  Migration and Chaining