Oracle FAQ Your Portal to the Oracle Knowledge Grid

Home -> Community -> Usenet -> c.d.o.server -> Re: switching to 'direct path read' should help prevent thrashing buffer cache ?

Re: switching to 'direct path read' should help prevent thrashing buffer cache ?

From: bdbafh <>
Date: 20 Dec 2006 16:20:58 -0800
Message-ID: <>

On Dec 20, 5:21 pm, wrote:
> Folks,
> Our environment is neither an OLTP nor a DSS system. We have
> transactions that cross boundaries.
> Particularly we have these one of jobs that many of our customers run
> at any time during the
> day in which they chose to clear a table column.
> Most clients clear anywhere from 1 million rows to 11 million rows
> per job.
> The pseudo-code and SQL looks like this:
> while SQL%ROWCOUNT < 500,000
> do
> set col1= null,
> col2= null,
> col3= null
> WHERE ( col1 is not null OR
> col2 is not null OR
> col3 is not null ) AND ROWNUM <= 500,000;
> commit;
> done.
> We use a ROWNUM limit in order to prevent row blocking for other
> processes that
> might be processing single row dml against the table ..
> We have increased the efficiency of these processes .. making IO
> faster and now customers
> are just doing it more often. ... this obviously thrashes my buffer
> cache.
> Nearly all updates spend most of their time waiting on 'db file
> scattered read'.
> We have db_file_multiblock_read_count = 128.
> Should also mention that this process connects via a shared/mts
> connection... although
> we can change that if needed.
> I'm thinking about having just this process run in parallel in order to
> bypass the buffer cache because, I don't believe this process benefits
> from caching and it causes blocks to age out faster for other clients
> that are doing other things .. and do benefit from caching.
> My thought is that if I switch this to a dedicated connection and I
> add a PARALLEL hint
> ( even if it's just 2 parallel servers per job), the job will
> complete faster, it will prevent my cache from being thrashed only at
> the cost of more pga memory , and a little bit more io.
> I'm looking for the cons in doing something like this?

Had an oracle version been posted, someone might be able to post a note about the use of array processing, such as BULK COLLECT. But as no oracle version information was posted no one will likely do so.

-bdbafh Received on Wed Dec 20 2006 - 18:20:58 CST

Original text of this message