From: Edoardo Serra <osdevel@webrainstorm.it>
To: pgsql-performance@postgresql.org
Subject: Postmaster using only 4-5% CPU
Date: Tue, 21 Mar 2006 13:46:16 +0100
Message-ID: <7.0.0.16.2.20060321115738.060f9078@webrainstorm.it> (raw)
Hi all,
I'm having a very strange performance
problems on a fresh install of postgres 8.1.3
I've just installed it with default option and
--enable-thread-safety without tweaking config files yet.
The import of a small SQL files into the DB (6
tables with 166.500 total records, INSERT syntax)
took me more than 18 minutes as shown below
(output of "time ./psql benchmarks < dump.sql")
real 18m33.062s
user 0m10.386s
sys 0m7.707s
The server is an
- Intel(R) Xeon(TM) CPU 3.60GHz - 1MB L2
- 1 GB RAM
- 2x HDD SCSI U320 RAID 1 Hardware (HP 6i controller)
The same import, tried on an another low-end
server with a fresh install of postgres 8.1.3 gave me:
real 2m4.497s
user 0m6.234s
sys 0m6.148s
During the test, the postmaster on the first
server (the slow one) uses only a 4% CPU, while
on the second one it reaches 50% cpu usage
I was thinking on a IO bandwidth saturation, but
"vmstat 1" during the import shows me small values for io/bo column
Searching the archive of the ml I found a Disk IO
test I suddenly ran on the slower server as follow
# time bash -c "dd if=/dev/zero of=bigfile bs=8k
count=200000 && sync" (write test)
# time dd if=bigfile of=/dev/null bs=8k (read test)
output of "vmstat 1" during the above test follows:
procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
Write test
0 11 540 2344 12152 863456 4 0 340 27848 1709 695 6 53 0 41
0 11 540 2344 12180 863516 4 0 44 45500 1623 386 0 2 0 98
0 5 540 3168 12200 862520 0 0 264 44888 1573 315 1 2 0 97
Read test
0 2 440 2328 6076 849120 0 0 94552 0 1550 624 3 10 0 87
0 2 440 2248 6104 848936 0 0 94508 0 1567 715 7 10 0 83
0 3 440 2824 6148 847828 0 0
102540 448 1511 675 14 11 0 75
Values of io/(bi-bo) during the disk test are a
lot higher than during the import operation....
I really have no more clues .... :(
Do you have any ideas ?
Tnx in advance
Regards
Edoardo Serra
WeBRainstorm S.r.l.
IT, Internet services & consulting
Via Pio Foà 83/C
10126 Torino
Tel: +39 011 6966881
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To: pgsql-performance@postgresql.org
Cc: osdevel@webrainstorm.it
Subject: Re: Postmaster using only 4-5% CPU
In-Reply-To: <7.0.0.16.2.20060321115738.060f9078@webrainstorm.it>
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