Re: I/O and db_file_multiblock_read_count
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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