Hi,
I'm experiencing extremely different response times for some complex pgsql functions. extremly different means from 20ms - 500ms and up to 20s.
I have to say that the complete database fits in memory (64GB).
shared_buffers is set to 16GB. the rest ist used by thefs cache and conections/work_mem.
the server is running under linux rhel5 and is 8.4.5.
the filesystem is ext3 due to the lack of xfs support by redhat.
- I have for the one function response time of 20 ms with no shared blocks read.
- If there are shared blocks to be read I get immediatly response time of at least 80ms and up to 200ms.
- If i see page reclaims I always get response times above 400ms
- I'm guessing that 20s response time come together with i/o.
As far as I read page reclaims occur probably here, because fs cache has to free memory for allocations for the client. Am I right?
So how can i prevent page reclaims?
What do the number is within the brackets mean e.g. 0/3330 [0/4269] page faults/reclaims?
Or is this output somewhere explained? I didn't find anything.
best regards,
Uwe
this is one output of an execution without page reclaims:
LOG: EXECUTOR STATISTICS
DETAIL: ! system usage stats:
! 0.071247 elapsed 0.053992 user 0.016998 system sec
! [0.056991 user 0.018997 sys total]
! 0/0 [0/0] filesystem blocks in/out
! 0/3330 [0/4269] page faults/reclaims, 0 [0] swaps
! 0 [0] signals rcvd, 0/0 [0/0] messages rcvd/sent
! 0/0 [8/0] voluntary/involuntary context switches
! buffer usage stats:
! Shared blocks: 1 read, 0 written, buffer hit rate = 99.97%
! Local blocks: 0 read, 0 written, buffer hit rate = 0.00%
! Direct blocks: 0 read, 0 written
Time: 73.154 ms
this is one output of an execution with page reclaims:
LOG: EXECUTOR STATISTICS
DETAIL: ! system usage stats:
! 0.627502 elapsed 0.461930 user 0.075988 system sec
! [0.465929 user 0.078987 sys total]
! 0/0 [0/0] filesystem blocks in/out
! 0/20941 [0/21893] page faults/reclaims, 0 [0] swaps
! 0 [0] signals rcvd, 0/0 [0/0] messages rcvd/sent
! 12/7 [20/7] voluntary/involuntary context switches
! buffer usage stats:
! Shared blocks: 48 read, 0 written, buffer hit rate = 99.72%
! Local blocks: 0 read, 0 written, buffer hit rate = 0.00%
! Direct blocks: 0 read, 0 written
Time: 629.823 ms
