Gregory Stewart wrote:
Hello,
We are currently developing a web application and have the webserver and
PostgreSQL with our dev db running on a machine with these specs:
Win 2003 standard
AMD Athlon XP 3000 / 2.1 GHZ
2 Gig ram
120 gig SATA HD
PostgreSQL 8.1.0
Default pgsql configuration + shared buffers = 30,000
The performance of postgresql and our web application is good on that
machine, but we decided to build a dedicated database server for our
production database that scales better and that we can also use for internal
applications (CRM and so on).
To make a long story short, we built a machine with these specs:
Windows 2003 Standard
AMD Opteron 165 Dual Core / running at 2 GHZ
2 gig ram
2 x 150 Gig SATA II HDs in RAID 1 mode (mirror)
PostgreSQL 8.1.3
Default pgsql configuration + shared buffers = 30,000
Perfomance tests in windows show that the new box outperforms our dev
machine quite a bit in CPU, HD and memory performance.
I did some EXPLAIN ANALYZE tests on queries and the results were very good,
3 to 4 times faster than our dev db.
However one thing is really throwing me off.
When I open a table with 320,000 rows / 16 fields in the pgadmin tool (v
1.4.0) it takes about 6 seconds on the dev server to display the result (all
rows). During these 6 seconds the CPU usage jumps to 90%-100%.
When I open the same table on the new, faster, better production box, it
takes 28 seconds!?! During these 28 seconds the CPU usage jumps to 30% for 1
second, and goes back to 0% for the remaining time while it is running the
query.
What is going wrong here? It is my understanding that postgresql supports
multi-core / cpu environments out of the box, but to me it appears that it
isn't utilizing any of the 2 cpu's available. I doubt that my server is that
fast that it can perform this operation in idle mode.
I played around with the shared buffers and tried out versions 8.1.3, 8.1.2,
8.1.0 with the same result.
Has anyone experienced this kind of behaviour before?
How representative is the query performance in pgadmin?
Pgadmin can give misleading times for queries that return large result
sets over a network, due to:
1/ It takes time to format the (large) result set for display.
2/ It has to count the time spent waiting for the (large) result set to
travel across the network.
You aren't running Pgadmin off the dev server are you? If not check your
network link to dev and prod - is one faster than the other? (etc).
To eliminate Pgadmin and the network as factors try wrapping your query
in a 'SELECT count(*) FROM (your query here) AS a', and see if it
changes anything!
Cheers
Mark
