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Re: multiple dbwr's and deadlock

From: James Mu <jamesmu_ca_at_yahoo.ca>
Date: Tue, 8 May 2001 07:27:56 +0800
Message-ID: <3MQJ6.1494$h%.788462@news20.bellglobal.com>

Hi,

    I have some questions about Anjo's post. I think there is a basic principal that is db_writer_processes should equal or less than the number of the cpus. And if your system support AIO, maybe this problem will be some relief.

James
Anjo Kolk <k.kolk_at_chello.nl> wrote in message news:3AF79C25.1EAE31E_at_chello.nl...
>
> Here is the problem that you *could* be facing:
>
> 1) multiple insert process make buffers dirty in a rate that is higher
 than the
> DBWR(s) can write out
> 2) at some stage the insert processes will wait on the DBWR(s).
> 3) such a wait will most likely be in the middle of an insert when you are
> holding other resources (memory and enqueues)
> 4) increase the number of DBWR(s) and you problems could go away (assuming
 that
> you have locking problems because of this).
>
> Infact I just had the same scenario at a customer site. They complained
 about
> 'hanging locks' (some process would hold on too locks for a long time and
> others would wait very long). So they assumed a locking problem. The
 locking
> problem in their case was a symptom of not having enough DBWRs.
>
> So what to do in your case:
>
> 1) db_block_lru_latches = 4-8
> 2) db_writers = 16 or even higher
> 3) _db_block_write_batch = <something decent, less than (db_files *
> db_file_multi_block_read_count)/2).
>
> Anjo.
>
>
> James Mu wrote:
>
> > hi,
> > You ask a big question. To let it some clear, I think you should
 record
> > the ora number, then go to metalink to query some info.
> > James
> >
> > Maurice Samuels <samuels_at_red.seas.upenn.edu> wrote in message
> > news:9crsph$o3r$1_at_netnews.upenn.edu...
> > > hi,
> > > recently i turned on multiple dbwr's (4) and increased the
 db_block_lru_latches (24) on an 8-CPU Sun 5500
> > > server with 8G of memory (oracle 8.0.x). a few times when i've tried
 to
 run 5 insert /*+append ..
> > > operations, i get
> > > deadlock messages written to the alert.log and some of the operations
 outright fail. but i have no problems
> > > running 4 of those types of operations at a time (is this related to
 how
 many writer's there are).
> > > had anyone ever run into anything like this?
> > > what performance views should i be watching to see how oracle is
 managing
 the buffer cache and locks?
> > > can anyone point to a good book on the topic of multiple dbwr's and
 locks?
> > > the oracle documentation regarding the multiple dbwr's is a bit
 confusing
 on this topic.
> > > thanks in advance
> > > -maurice
> > > samuels_at_seas.upenn.edu
>
>
>
>
>
Received on Mon May 07 2001 - 18:27:56 CDT

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