On 10/15/2008 01:55 PM, Lars Eilebrecht wrote: > Hi, > > I'm trying to debug a performance issue on an Apache infrastructure > using 2.2.9 as reverse proxies. The Apache servers don't do much > except for ProxyPass'ing data from others backend servers, and > caching the content using mod_mem_cache.
Is it really a good idea to use mod_mem_cache? Keep in mind that mod_mem_cache uses local caches per process and cannot use sendfile to send cached data. It seems that mod_disk_cache with a cache root on a ram disk could be more efficient here. > This is Apache with the worker mpm on Solaris. Currently each > box is configured with a ServerLimit of 3. The attached screenshot > of the server-status page shows that almost all threads of one > child process (at the bottom) are in "W" state. The thread status > of the process shown at the top look OK, but the second child > process doesn't seem to be used at all. > The first odd thing is that I would have expected that Apache > uses all child processes about equally. Especially I would > have expected that there are at least 25 threads for the second > process in state "_" (waiting for connection), because the > MinSpareThread directive is set to 25. This is indeed strange. Mind to 1. Attach an ASCII-output of the whole status page to see the exact process / thread slot usage. 2. Your MPM configuration and your reverse proxy configuration. > The second odd thing is that the connections/threads in W state > seem to be hanging, i.e., no data is being transferred over the > connection and these threads/connection time out after about 256 > seconds. However, the general Timeout setting is 30s so why > isn't the connection killed after 30s? It would be very helpful to have a backtrace of this process. If they aren't killed after the timeout it is highly likely that they don't wait for IO but do or wait for something else. > What happens during peek times is that all threads of one > child process end up in state W, then Apache starts using > another child process, etc. and at some point basically > all threads are in state W and we are hitting the MaxClients > limit which makes the server unusable. Regards Rüdiger
