I run postfix and have it connected to postgresql for just about
everything. Postfix is very sloppy on the database side, or so it seems.
I ended up having to configure postfix to limit the number of
processes it will start, and then make sure postgres has more than
that connections available too.
In postfix, I set "default_process_limit = 10" in main.cf. In
postgresql, I set max connections to 256, with 4 reserved for super
user. My mail volume also isn't too bad, typically, so I can get away
with setting this to 10. In some cases, I think each postfix process
is opening a new database connection for every lookup. And, if a
process needs to lookup 2 or 3 items, it uses new connections for
every one. Then, the connections don't get closed until those
processes are killed a little while later.
Pure speculation, but it's about the only thing I can think of (short
of going through and analyzing the source code) that would explain
the disparity between postfix processes and postgres connections.
With that, I have the following in ps (after running for a while, so
things are mostly stable):
Postgres Connections (not including stats): 43
Postfix:
transport: 15
virtual: 13
mailbox: 8
domains: 2
Courier IMAP/POP
courier: 5
These numbers will fluctuate with mail traffic. And, they do not
correspond with the open # of postfix processes (19 processes: 1
master, 1 qmgr, 2 trivial rewrite, 7 smtpd, 6 cleanup, 1 pickup, 1
virtual).
That leads me to believe that the postfix database interface (for
postgres at least) is pretty sloppy. I've been planning to try a
pooling program, just to see if that would make a difference, but I
haven't had time to do any research or practical testing to find
out. Does anyone know if this problem occurs when using postfix with
LDAP servers or mysql ?
Thanks,
Greg
On Jun 21, 2005, at 12:00 PM, Sven Willenberger wrote:
We have a system set up whereby postfix and maildrop gather user info
from a pg database (7.4.2 on FreeBSD 5.2.1) to do local mail
acceptance
and delivery. I have configured max connections at 512 but I find that
this is not enough and I get "connection limit exceeded for
non-superusers" errors. I see upon ps ax that there are hundreds of
idle
connections (state I).
Is there any way on the server end to close these connections (the
process is apparently for postfix and then maildrop to open a
connection, run one select statement, and supposedly close the
connection). If not, would pgpool help in this case? Since all the
connections are basically 2 users (one for the mail delivery system
and
another for the mail retrieval), are there any such "connections"
limitation by pgpool (i.e. if we get a spike of 700-1000 queries each
with their own "connection")?
Thanks,
Sven
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