Row Migration

Giganews Newsgroups
Subject: Row Migration
Posted by:  Rahul (rahul.nimmagad…@gmail.com)
Date: Wed, 18 Jul 2007

Hello all,

I have the following doubt regarding Row Migration. First let me
explain my understanding of Row Migration -- When the space in a
particular block is not sufficient to accommodate a row growing as a
result of an update operation because of the low value of PCTFREE,
results in Row Migration. Then the oracle server will move the entire
row to a new block and leave a pointer from the original block to the
new location. This results in the decrease of I/O performance.

My Query --
Instead of having a pointer from the original block to the new block,
why doesn't oracle server delete the information about that particular
row in the row directory slot of the original block and put the
information about the row in the row directory slot of the new block
as it is anyway moving the entire row to a new block. This can
increase I/O performance as the number of I/Os required are less than
the previous scenario.

Thanking you,
Rahul.

Replies