Looking at source, I see that Jeff's patch, and the 'ttl' parameter in general, is only referenced under '#if APR_HAS_THREADS'.  When I load-tested and found the timeouts, I was testing under Apache 2.2 Prefork, and thus that patched code is not even compiled, IIUC.

However I would still like to know what that parameter is for when running under Worker.

I think the implication of my source journey is also that if my module instantiates multiple threads under Prefork (which it does), it must call apr_memcache* routines from only one of them.  Is that correct?


On Wed, Sep 26, 2012 at 7:17 PM, Joshua Marantz <jmarantz@google.com> wrote:
+dev (sorry for the duplicate; my first attempt failed due to not being a subscriber).

Keeping modules-dev on CC if that's appropriate.

Thanks, Jeff, I was wondering if there was a units issue there.  I'm still wondering if anyone can describe the meaning of that argument in more detail.  Is that related to my multiget APR_TIMEUP returns?   The phrase "time to live of client connection" confuses me.  Would it be inaccurate to instead say "the maximum number of seconds apr_memcache is willing to wait for a single operation?  Or does it mean *both*, implying that a fresh TCP/IP connection is made for every new operation, but will stay alive for only a certain number of seconds.

I have a practical question about how I release software given this change.  Our module (mod_pagespeed) is documented to run with Apache 2.2 and Apache 2.4.  It seems like for 2.2 I should probably multiple my desired argument by a million.  Same with for 2.4.x and earlier, for some value of x.  How should I work this in my code?  Should I query the version number using an apr utility or something and multiply by a million in certain cases?

What's the best practice calling this function for module developers?


On Wed, Sep 26, 2012 at 6:20 PM, Jeff Trawick <trawick@gmail.com> wrote:
On Wed, Sep 26, 2012 at 5:38 PM, Joshua Marantz <jmarantz@google.com> wrote:
> Hi,
> I've been having some success with the apr_memcache_* functions.  In
> load-tests, however, I'm finding a lot of timeouts
> with apr_memcache_multgetp.  Specifically, the status returned with the
> individual elements is APR_TIMEUP.
> This leads me to wonder what the significance of the second to last arg to
> this function is:
> apr_memcache_server_create(
>           pool_, hosts_[i].c_str(), ports_[i],
>           kDefaultServerMin, kDefaultServerSmax,
>           thread_limit_, kDefaultServerTtlUs, &server);
> I have kDefaultServerSmax initialized to 600, as that's the value I found
> in mod_socache_memcache.c   But that seems stingy (if it's really in
> microseconds).  Should I be giving that a few hundred millis instead?
> http://apr.apache.org/docs/apr-util/1.4/group___a_p_r___util___m_c.html#ga18ddd72bc1ab5edb0a08a8f26f193bd3
> claims
> that means "time to live of client connection" but I don't understand what
> that phrase means exactly, or if it relates to the APR_TIMEUP returns I've
> been suffering from.
> My code is here;
> http://code.google.com/p/modpagespeed/source/browse/trunk/src/net/instaweb/apache/apr_mem_cache.cc
> -Josh

dev@apr.apache.org is a better place to ask about details of apr functions.

Coincidentally, earlier today I committed someone's fix for the
confusion about the units of ttl:


It is supposed to be in seconds.  Pick up the tiny change to
apr_memcache.c and see if that helps anything.  You should continue
this discussion on dev@apr.apache.org.

Born in Roswell... married an alien...