On 1/24/07, Heikki Linnakangas <[EMAIL PROTECTED]> wrote:
Pavan Deolasee wrote: > I have just counted the number of read/write calls on the CLOG blocks. As > you can > see the total number of CLOG reads jumped from 545323 to 1181851 i.e. > 1181851 - 545323 = 636528 CLOG block reads for 1554697 pages of stock > table. Hmm. So there is some activity there. Could you modify the patch to count how many of those reads came from OS cache? I'm thinking of doing a gettimeofday() call before and after read, and counting how many calls finished in less than say < 1 ms. Also, summing up the total time spent in reads would be interesting.
Here are some more numbers. I ran two tests of 4 hour each with CLOG cache size set to 8 blocks (default) and 16 blocks. I counted the number of read() calls and specifically those read() calls which took more than 0.5 ms to complete. As you guessed, almost 99% of the reads complete in less than 0.5 ms, but the total read() time is still more than 1% of the duration of the test. Is it worth optimizing ? CLOG (16 blocks) reads(743317), writes(84), reads > 0.5 ms (5171), time reads (186s), time reads > 0.5 ms(175s) CLOG (8 blocks) reads(1155917), writes(119), reads > 0.5 ms (4040), time reads (146s), time reads > 0.5 ms(130s) (amused to see increase in the total read time with 16 blocks) Also is it worth optimizing on the total read() system calls which might not cause physical I/O, but still consume CPU ? Thanks, Pavan EnterpriseDB http://www.enterprisedb.com
