Buffer busy waits

Buffer busy waits occur when a session cannot access a needed block because it is in use by another session. 

The two most common causes are:

  • insufficient free lists for a table, or
  • too few rollback segments.

If buffer busy waits are significant, check the category of events being waited for on Spotlight on Oracle's Wait activity tab.

If most buffer waits are for data blocks, then it is likely that you need to create multiple freelists (using the FREELIST clause of the CREATE TABLE statement) for tables that are subject to very heavy concurrent inserts. If the leading category is for Undo Header or Undo Block, you may need to create additional rollback segments.

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