denis@xxxxxxxxxxx wrote:
We have a postgresql server configured with max_connections=4096.
We have such a high number of max_connections because there are 8 web
servers connected to the database and all use persistent connections.
Each web server can have 256 max clients and 2 connection strings, so
the max connections to the db is 256 * 8 * 2=4096.
The one-word answer is "pgpool" http://pgpool.projects.postgresql.org/
You don't really want them all using persistent connections directly to
the DB.
To start the postgresql, I must to do some kernel extra configuration:
kernel.shmmax = 1165063808
kernel.sem=512 64000 100 512
and the parameters i changed other than max_connections in the
postgresql.conf are:
- shared_buffers = 131072
That's a *very* big shared_buffers value. Try reducing it by a factor of
10 and reading the "performance tuning" article here:
http://www.varlena.com/varlena/GeneralBits/Tidbits/index.php
- checkpoint_segments = 32
We are doing pre-production tests and we encountered the following
problems:
- The database server is generally low loaded except when the postgres
recycles a transaction log file.
Your disk I/O is probably saturated. However, fix your configuration
settings before worrying about hardware.
- This causes the apache frontends to slow down and to do all together
the most heavy operation (that is five inserts in five different tables
and a delete)
- After some time the postgresql starts giving the message "WARNING:
there is already a transaction in progress". It seems like the apache
frontend didn't close correctly the previous connection living a
transaction open but I'm not sure this is the only problem.
Sounds like a BEGIN being re-issued alright. Solution - fix your
application(s) and don't use persistent connections (or if you do, make
sure you rollback any pre-existing transactions and issue any relevant
SET commands).
--
Richard Huxton
Archonet Ltd
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