Why are my httpd mpm_prefork processes being reaped so quickly?
- by Dan Pritts
We've got a system running RHEL6, x64. We are using a local installation of apache 2.2.22 from source. we serve primarily:
mod_perl applications (with a local installation of perl 5.16.0)
tomcat applications proxied with mod_jk
Here is some context; the main question is below.
All of this talks to an Oracle backend.
We are having issues with Oracle becoming unresponsive. We think this is because we're hitting the maximum process limit in oracle. We've upped the process limit, but now we are hitting memory pressure on the oracle server. We have tons of oracle sessions sitting idle. I can trace a bunch of them back to the httpd processes.
We have mod_perl's Apache::DBI start up a new connection to the database with each httpd child that's spawned. We are concerned that these are not always getting closed out properly when the httpd's exit...and the httpd's are exiting very frequently. I know that it would be good to modify the mod_perl applications to use some better form of db connection pooling; we plan to pursue that but would like to solve our immediate problem sooner.
So here's the main question.
We are using the prefork MPM.
The apache child processes are lasting at most a few minutes. Log analysis shows that each one is serving fewer than 50 clients before exiting; the last request each child serves is OPTIONS * HTTP/1.0 on some sort of internal connection; I'm under the impression that this is a "ping" from the master process.
I've adjusted the MPM config as follows. I didn't want to raise MinSpareServers too high, because, after all, i'm trying to minimize the number of sessions to oracle.
MinSpareServers 5
MaxSpareServers 30
MaxClients 150
MaxRequestsPerChild 10000
Right now we're serving 250-300 requests per minute.
We've got 21 httpd's running, the eldest (other than the master, owned by root) being 3 minutes old.
This rate of reaping of the apache children really seems excessive. What could be causing it?
Apache was built with:
$ ./configure --prefix=/opt/apache --with-ssl=/usr/lib --enable-expires --enable-ext-filter --enable-info --enable-mime-magic --enable-rewrite --enable-so --enable-speling --enable-ssl --enable-usertrack --enable-proxy --enable-headers --enable-log-forensic
Apache config info:
% /opt/apache/bin/httpd -V
Server version: Apache/2.2.22 (Unix)
Server built: Jul 23 2012 22:30:13
Server's Module Magic Number: 20051115:30
Server loaded: APR 1.4.5, APR-Util 1.4.1
Compiled using: APR 1.4.5, APR-Util 1.4.1
Architecture: 64-bit
Server MPM: Prefork
threaded: no
forked: yes (variable process count)
Server compiled with....
-D APACHE_MPM_DIR="server/mpm/prefork"
-D APR_HAS_SENDFILE
-D APR_HAS_MMAP
-D APR_HAVE_IPV6 (IPv4-mapped addresses enabled)
-D APR_USE_SYSVSEM_SERIALIZE
-D APR_USE_PTHREAD_SERIALIZE
-D SINGLE_LISTEN_UNSERIALIZED_ACCEPT
-D APR_HAS_OTHER_CHILD
-D AP_HAVE_RELIABLE_PIPED_LOGS
-D DYNAMIC_MODULE_LIMIT=128
-D HTTPD_ROOT="/opt/apache"
-D SUEXEC_BIN="/opt/apache/bin/suexec"
-D DEFAULT_PIDLOG="logs/httpd.pid"
-D DEFAULT_SCOREBOARD="logs/apache_runtime_status"
-D DEFAULT_LOCKFILE="logs/accept.lock"
-D DEFAULT_ERRORLOG="logs/error_log"
-D AP_TYPES_CONFIG_FILE="conf/mime.types"
-D SERVER_CONFIG_FILE="conf/httpd.conf"
modules are compiled into apache rather than shared libs:
% /opt/apache/bin/httpd -l
Compiled in modules:
core.c
mod_authn_file.c
mod_authn_default.c
mod_authz_host.c
mod_authz_groupfile.c
mod_authz_user.c
mod_authz_default.c
mod_auth_basic.c
mod_ext_filter.c
mod_include.c
mod_filter.c
mod_log_config.c
mod_log_forensic.c
mod_env.c
mod_mime_magic.c
mod_expires.c
mod_headers.c
mod_usertrack.c
mod_setenvif.c
mod_version.c
mod_proxy.c
mod_proxy_connect.c
mod_proxy_ftp.c
mod_proxy_http.c
mod_proxy_scgi.c
mod_proxy_ajp.c
mod_proxy_balancer.c
mod_ssl.c
prefork.c
http_core.c
mod_mime.c
mod_status.c
mod_autoindex.c
mod_asis.c
mod_info.c
mod_cgi.c
mod_negotiation.c
mod_dir.c
mod_actions.c
mod_speling.c
mod_userdir.c
mod_alias.c
mod_rewrite.c
mod_so.c
One final note - the red hat httpd, apr, and perl packages are all installed, but ldd shows that none of those libraries are linked with the running httpd.
