Re: I/O and db_file_multiblock_read_count
- From: Kevin Lidh <kevin.lidh@xxxxxxxxx>
- To: Mladen Gogala <mgogala@xxxxxxxxxxx>
- Date: Mon, 11 Dec 2006 07:50:42 -0700
At this time, we don't have system statistics. I built a million+ row
table and didn't give it an index. I then did a select which was an
equivalent of "SELECT *" to force a full-table scan. My goal was/is to
find the optimal setting for the db_file_multiblock_read_count
parameter. I was mostly just surprised that it was faster to grab the
same group of data in pieces than in one fell swoop. My guess was that
the underlying physical I/O (not what Oracle perceived as an I/O) was
actually multiple reads from the disk and that the process of presenting
them as a singular response comprised the addition time.
On Sat, 2006-12-09 at 00:35 -0500, Mladen Gogala wrote:
> On 12/08/2006 03:46:00 PM, Kevin Lidh wrote:
> > I was reading an article about the appropriate setting for
> > db_file_multiblock_read_count. I'm on a HP-UX 11.11 64-bit system with
> > Oracle 9.2.0.7.0. The original value was 16 and I bounced the database and
> > ran a million record full-scan test (10046 trace) and then set the value to
> > 128 (max value) and re-ran the test. Although I did have less calls to 'db
> > file scattered read' (140 compared to 1008), the time to get the same number
> > of blocks was longer. A random example from the trace files looks like
> > this:
>
> Of course, you did run dbms_stats.gather_system_stats?
>
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