Re: I/O and db_file_multiblock_read_count
- From: Hemant K Chitale <hkchital@xxxxxxxxxxxxxx>
- To: kevin.lidh@xxxxxxxxx, mgogala@xxxxxxxxxxx, knecht.stefan@xxxxxxxxx
- Date: Sat, 09 Dec 2006 16:18:57 +0800
I don't undersetand Mladen's and Stefan's recommendations about
running dbms_stats.gather_system_stats.
Kevin says that he deliberately ran a test to check the performance
of multiblock reads.
He is not asking "how can I avoid multiblock reads ?".
He is asking "why is the total time for 128-block reads not
significantly lesser than the total time for 16-block reads ?".
Hemant
On 12/8/06, Kevin Lidh
<<mailto:kevin.lidh@xxxxxxxxx>kevin.lidh@xxxxxxxxx> 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:
<snip>
And I ran the test again with 16 after my 128 test and the results
were similar to the first test. The cumulative times for the 'db
file scattered read' was 1.3181s for the 16 and 2.5149s when it was
128. We use a Hitachi SAN and I know it has caching but I would
still think that the fewer, bigger requests would be faster. Is
there a measurement or setting on the operating system or even SAN
that I can look at to help determine the optimal setting?
Hemant K Chitale
http://web.singnet.com.sg/~hkchital
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