RE: buffer busy wait & latch free ( cache buffer chain )

If on 8.1.7, there are several bugs relating to waiting for latch-free on cache-buffer-chains, and the possibility of the instance hanging.

One is 1967363, and at least two others are still open after applying that patch.

Changing cache buffer latches/buckets is not mentioned in those bugs, and since they are underscored, I would approach with caution.

>>> dcutrone_at_afip.gov.ar 12/05/01 08:30AM >>>
Vivek:

    To combat the latch free- cache buffer chain problem, I would first check in v$latch_children if the contention is even across all cache buffer chain latches. If this is the case case (most of the time it is not) , I would add more cache buffer latches. If this is not the case, as ARUN suggested, I would find out which buffers are hot and I would investigate WHY they are hot. (Ussually because of a bad SQL-- you should fix them! )

    According to BBW problem, try to identify the segment involved and the cause (p1=file , p2=block and p3=cause from a 10046 trace) and then according to p3 there are some changes that can be done.

HTH
Diego

• Original Message ----- To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com> Sent: Tuesday, December 04, 2001 9:35 AM

> What are u seeing the buffer busy waits on is it for the read intensivity
> and latch free is showing that there are hot blocks why dont you find out
> the hot blocks and find what can be done about it
>
>
> >From: "VIVEK_SHARMA" <VIVEK_SHARMA_at_infy.com>
> >Reply-To: ORACLE-L_at_fatcity.com
> >To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
> >Subject: buffer busy wait & latch free ( cache buffer chain )
> >Date: Tue, 04 Dec 2001 01:55:19 -0800
> >
> >
> >In report.txt we are getting the wait
> >"buffer busy wait" _& wait on "latch free" for "cache buffer chain"
> >
> >Could an excessively Large db_block_buffer cause this ?
> >
> >NOTE - Transaction OLTP in nature
> >
> >NOTE - freelists is set = 2* cpu_count
> >
> >Any oher advice ?
> >

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Author: Binley Lim
  INET: Binley.Lim_at_ird.govt.nz

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