There are 3 classic situations:
1) DBWR hasn't finished writing to the disk yet. 2) Block is locked by another node (OPS, RAC). 3) RMAN is writing the block. That's right, RMAN locks (pins) blocks in memory, otherwise it couldn't ensure consistent backup. That is the reason why RMAN doesn't need "alter tablespace begin backup" command.
To make the long story short, there is a note on metalink (Note:155971.1) with
an appropriate title: Resolving Intense and "Random" Buffer Busy Wait
Performance Problems. Buffer busy waits are usually a consequence of I/O subsystem not being to provide enough throughput to the database. What can you
do with v$filestat? You can find where are your hot spots and fix the problem.
On 2003.07.29 17:24, [EMAIL PROTECTED] wrote:
Folks,
Say a session issues a read request, and finds another session already reading the block into the buffer cache. If this session waits N ms on a "buffer busy waits" event, does this N ms of wait get added to the read times in v$filestat? Or is the readtim in v$filestat purely physical I/O?
Thanks Raj
-- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: INET: [EMAIL PROTECTED]
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-- Mladen Gogala Oracle DBA -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Mladen Gogala INET: [EMAIL PROTECTED]
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