【等待事件】buffer busy waits

Reducing Waits / Wait times:

As buffer busy waits are due to contention for particular blocks then you cannot take any action until you know which blocks are being competed for and why. Eliminating the cause of the contention is the best option. Note that "buffer busy waits" for data blocks are often due to several processes repeatedly reading the same blocks (eg: if lots of people scan the same index) - the first session processes the blocks that are in the buffer cache quickly but then a block has to be read from disk - the other sessions (scanning the same index) quickly 'catch up' and want the block which is currently being read from disk - they wait for the buffer as someone is already reading the block in.

The following hints may be useful for particular types of contention - these are things that MAY reduce contention for particular situations:

Block Type	Possible Actions
data blocks	Eliminate HOT blocks from the application. Check for repeatedly scanned / unselective indexes. Change PCTFREE and/or PCTUSED. Check for 'right- hand-indexes' (indexes that get inserted into at the same point by many processes). Increase INITRANS. Reduce the number of rows per block.
segment header	Increase of number of FREELISTs. Use FREELIST GROUPs (even in single instance this can make a difference).
freelist blocks	Add more FREELISTS. In case of Parallel Server make sure that each instance has its own FREELIST GROUP(s).
undo header	Add more rollback segments.

確定引起該等待的BLOCK或型別可以參照:

Resolving Issues Where ''buffer busy waits' When Concurrency for Buffers is High (Doc ID 1476043.1)
How to Identify The Segment Associated with Buffer Busy Waits (Doc ID 413931.1)