[Advisory] Old PHP client very buggy...
sean at chittenden.org
Fri Dec 17 10:48:55 PST 2004
I know it's late for a Halloween story, but save it so you can pull it
out next year during October and scare some php kiddies. Running
across this bug was spooky and hard to diagnose.
I'd like to advise all users of the native PHP client distributed by
Danga to use the client posted by Timo Ewalds (plus the patch from Ian
Kallen). The URL for the original PHP client in question is:
I'm pretty sure they didn't write it, but since it's distributed by
danga.com, many folks get the wrong impression that it's the
authoritative or recommended client to use. The URL for the updated
client and its patch is:
The original PHP client is subject to an effective DoS wherein its
parsing of data from the memcached server was buggy and would cause the
client to hang forever. Timo's updated client doesn't suffer from this
Many users may not be bitten by this, but, if all of a sudden pages
start hanging, or there's a slow creeping growth of apache processes,
the likely culprit is this memcached client. Other symptoms include
maxing out database connections or other resources that apache may use,
but never release because the request never reaches the cleanup state.
This particular bug is hard to track if someone attaches ktrace(1) or
gdb(1) to the idle apache process, which is just that: completely idle.
I consider this to be a bug on PHP's socket implementation as well, not
just a bug in the original php memcached client. Apache's client
timeout is ignored when doing PHP's socket IO, which is rather bogus.
The client timeout in apache should be read by php and applied to all
socket IO when socket IO is performed via apache/mod_php, which would
prevent an infinite growth of apache processes and resource consumption
(database or otherwise). Having PHP do this for non-mod_php requests,
however, would be undesirable.
I haven't spent the time to look at why this is, only to suggest that
someone may want to either sit down and figure out where the problem is
with the above PHP client mentioned above or upgrade to Timo's version.
The only notable difference between the clients insofar as I have
noticed is the class name needs to be changed.
FWIW, I likely won't be spending much more time with the native PHP
client and will probably be adding libmemcache(3) support to the PEAR
version which would give the PEAR version multi-server support.
Anyway, have a nice day. -sc
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