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.
> 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
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()
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
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 ?