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Re: [Linux-cluster] optimising DLM speed?



On 24/02/11 22:40, Scooter Morris wrote:
Hi all. After two tries, we've modified our cluster so that all nodes have increased their dlm hash table sizes to 1024. Initially, I put the echos in /etc/init.d/gfs2, but it turns out that /etc/init.d/gfs2 is sort of a no-op: /etc/init.d/netfs mounts the gfs2 filesystems before /etc/init.d/gfs2 is ever called, so the echos need to be before netfs.


I created a new init.d script to apply the values immediately after cman is started - see attached files.

At any rate, we have noticed a significant perceived improvement in overall performance of the systems. Where before, it was common to see imap process in D wait -- sometimes hanging for long periods of time -- we have not seen that at all since updating the hash table size. So far, so good!

How much ram have you got and which version of gfs2 are you running?

vermagic:       2.6.18-238.1.1.el5 SMP mod_unload gcc-4.1




#!/bin/sh
#
# dlm_tune - enlarge hash tables which are too small by default on modern systems.
#
# chkconfig: 2345 23 99
# description:  Helps prevent having thousands of hash tables.
#
#

# Sanity checks.
[ -x /usr/sbin/readahead ] || exit 0

# Source function library.
. /etc/rc.d/init.d/functions

start() {
    echo -n $"Enlarging DLM hash sizes: "
    /usr/local/bin/tweakdlmhash.sh >/dev/null &
    echo_success
    echo
}

stop() {
   /bin/true
}

# See how we were called.
case "$1" in
    start)
	start
	;;
    stop)
	stop
	;;
    status)
        ;;
    restart)
	stop
	start
	;;
    condrestart)
	;;
    reload)
        ;;
    *)
	echo $"Usage: $0 {start|stop|status|restart|condrestart|reload}"
	;;
esac
exit $RETVAL

Attachment: tweakdlmhash.sh
Description: application/shellscript


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