Tales From A Lazy Fat DBA

Den of an Oracle DB Performance freak & a fan of Cassandra, MySQL and PostgreSQL …

  • Likes

    • 138,422
  • Archives

  • Categories

  • Subscribe

  • Advertisements
  • Prashant Dixit is the FatDBA

  • Follow Tales From A Lazy Fat DBA on WordPress.com
  • My Twitter Feeds

  • Disclaimer!

    FatDBA or Oracle ‘Ant’ is an independent web-blog/site.The experiences, Test cases, views, and opinions expressed in this website are my own and does not reflect the views or opinions of my employer.

    This site is independent of and does not represent Oracle Corporation in any way. Oracle does not officially sponsor, approve, or endorse this site or its content.
    Product and company names mentioned in this website may be the trademarks of their respective owners.

Shrinking Segments

Posted by FatDBA on February 7, 2013

Shrinking Segments:
The diagram in the slide describes the two phases of a table shrink operation. The first phase does the compaction. During this phase, rows are moved to the left part of the segment as much as possible. Internally, rows are moved by packets to avoid locking issues. After the rows have been moved, the second phase of the shrink operation is started. During this phase, the high-water mark (HWM) is adjusted and the unused space is released. The COMPACT clause is useful if you have long-running queries that might span the shrink operation and attempt to read from blocks that have been reclaimed. When you specify the SHRINK SPACE COMPACT clause, the progress of the shrink operation is saved in the bitmap blocks of the corresponding segment. This means that the next time a shrink operation is executed on the same segment, the Oracle database server remembers what has been done already. You can then reissue the SHRINK SPACE clause without the COMPACT clause during off-peak hours to complete the second phase.

Untitled

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

 
%d bloggers like this: