We have been having
the problem with memory usage creeping slowly upward that I've seen reported by
several others in this list. I read several of the threads on this topic in the
archives but, though there were a lot of theories floated, no firm conclusions
seemed to be drawn. Like the others, memory usage as reported by 'free' on the
'-/+ buffers/cache' line creeps steadily upward until the site crashes.
Restarting Zope frees most of the memory.
We're running RedHat
Linux 6.1, on a dual- 550M processor box with 256Mb of memory, Zope 2.1.4 using
Apache, mod-ssl and PCGI, ZMySqlDA 1.1.3. The ZODB holds only non-dynamic data,
all user data is kept in the MySQL data base.
I tried testing on
our development server while no one else was accessing the site with the 'free'
utility displaying memory use every 5 seconds in an attempt to find out what
activity caused memory usage to creep upward without coming back
down.
To cut to the chase,
I seem to have narrowed it down to access to the MySQL database from multiple
threads. As it happens, we have a very thin client piece that can access the
server through http outside the browser. Most use of the site is through a
browser, but this small client checks with the server occasionally for scheduled
tasks when the browser isn't up. In some cases, access through the browser will
use a plug-in to trigger the client to check immediately rather than waiting for
its infrequent poll interval.
After an afternoon
of testing, I discovered that, with no one else accessing the site, I could
access pages as fast as I was able through the browser only (no client) or
from the client only (sped up to poll every few seconds) with no memory creep.
But when both were running at once (as they normally do), the memory usage would
slowly creep up.
Other
details:
Letting the client
poll and query the MySQL database frequently while using the browser to access
only pages that did NOT access the DB resulted in no creep.
Having two people
simultaneously access pages that DID access the database without the client
running on either machine DID cause memory creep.
Having two people
access pages that did NOT access the database without the client running did NOT
cause memory creep.
Looks to me like
there is a memory leak when ZMySQLDA is accessed from multiple
threads.
Anyone have any
ideas on where I could go to pin this down
further?
