Kevin Grittner a Ãcrit :
adrien ducos <aducos@xxxxxxxxxxxxxxxx> wrote:
[rearranged somewhat]
The version of both databases is postgres 8.4.1
[sigh] You really should upgrade.
http://www.postgresql.org/support/versioning
http://www.postgresql.org/docs/8.4/static/release.html
I know I should but only my system administrator is allowed to do so, we
will soon change to postgres 9.1 anyway.
So I checked the memory on prod during my query execution:
vmstat
procs -----------memory----------
r b swpd free buff cache
0 1 1280 23320 6356 2975956
The swap is not used but something is a bit odd: the cache is
using 98% of the RAM
The first line in vmstat (which is all you get if you run it without
a number) is averages since the OS was booted. That's not usually
very helpful. What does this show?:
free -m
or run the query while watching the output from:
vmstat 1
So I did that also, and have the same results:
free -m
total used free shared buffers cached
Mem: 3042 3000 41 0 4 2896
-/+ buffers/cache: 99 2942
Swap: 1983 1 1982
same for vmstat 1 while runing the query
vmstat 1
procs -----------memory---------- ---swap-- -----io---- --system--
----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
0 0 1280 45752 4496 2963460 0 0 29 45 0 1 2 0 95 3
Almost everything is "cached", I read on some documents that cache means
linux uses the free memory to cache disk data (and avoid waisting the
free memory).
On the other hand, when I do ps -aux while the query is running I see
the query is using 17% of the RAM, so I guess it is using the RAM ok.
The question could be, why is linux marking that 95% of the memory is
cache while in the same time ps -aux shows my query uses 17% of the RAM.
the copy of files on the SAN is about 3 times faster than on the
development hard drive.
Copy time doesn't always correlate real well with database
performance. Have you tried running bonnie++ or similar?
Ok, we didn't check on that but we will. I'll see with my system admin
next week (he is on hollydays now). On the paper thought it is a SAN
composed of several velociraptors. It is supposed to be faster than a
normal and rather old hard drive (speed and access time).
Thanks,
Adrien
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Adrien DUCOS
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