Re: Sudden drop in DBb performance

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On 09/05/2011 09:39 AM, Tomas Vondra wrote:
On 5 Září 2011, 16:08, Gerhard Wohlgenannt wrote:
Below please find the results of vmstat 2 over some periode of time ..
with normal database / system load.

What does a "normal load" mean? Does that mean a time when the queries are
slow?

Are you sure the machine really has 48GB of RAM? Because from the vmstat
output it seems like there's just 32GB.

procs -----------memory---------- ---swap-- -----io---- -system--
----cpu----
   r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy
id wa
   0  0 1342168 336936 107636 31353512    0    0    14   183 1911 3426
2  1 93  4


1342168 + 336936 + 107636 + 31353512 = 33140252 ~ 31GB

BTW there's 1.3GB of swap, although it's not used heavily (according to
the vmstat output).

Otherwise I don't see anything wrong in the output. What is the size of
the database (use pg_database_size to get it)? Did it grow significantly
recently?

Tomas


Yeah, its interesting that it swapped in memory, but never out.  Looking at this vmstat, it does not look like a hardware problem.(Assuming "normal load" means slow queries)

Did it grow significantly recently?

That's a good thought,  maybe the stats are old and you have bad plans?  It could also be major updates to the data too (as opposed to growth).

Gerhard, have you done an 'explain analyze' on any of your slow queries?   Have you done an analyze lately?

-Andy

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