RE: Sessions are waiting on buffer busy wait with P3 value 130 in v$s

From: Steve Adams <steve.adams_at_ixora.com.au>
Date: Fri, 25 May 2001 08:40:19 -0700
Message-ID: <F001.0030F33A.20010525080941@fatcity.com>

Hi Sri,

If you can identify the segments involved from the p1 and p2 parameters and put those segments into a KEEP buffer pool you should be able to get a lot of relief. Failing that, or if they are too big, consider either increasing db_block_buffers if you can or setting _db_percent_hot_default to something like 80. That would allow up to 80% of the DEFAULT buffer pool to be used for hot buffers thereby improving the caching of the buffers that are causing you to wait.

@ Regards,
@ Steve Adams
@ http://www.ixora.com.au/
@ http://www.christianity.net.au/

-----Original Message-----
Sent: Friday, 25 May 2001 9:26
To: Multiple recipients of list ORACLE-L v$s

We've lot buffer busy waits in data block with P3 value 130 in V$session.

I've read about this in few notes, but still I do not understand few things.

P3=130 means:

---

Block is being read by another session and no other suitable block image was found, so we wait until the read is completed. This may also occur after a buffer cache assumed deadlock. The kernel can't get a buffer in a certain amount of time and assumes a deadlock. Therefore it will read the CR version of the block.

Does it mean that the block is being held in an incompatible mode by the first session or set of sessions reading it in shared mode, and current session is trying to lock it exclusively for a DML and waiting for the same.

What are steps we can take to avoid this types of buffer busy waits?

Thanks for your help.
Sri

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Author: Steve Adams
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Received on Fri May 25 2001 - 10:40:19 CDT