Neil, Thanks for the info but I am kinda confused as to why the sudden writeout occurs at 4 minutes if the default ext3 settings is to flush the journal every 5 seconds. Do you know what the correlation between these times would be. I have seen previous posts from you in which you described your fileservers also having write stalls at around 5 minute intervals. Did you figure out why things would go bad at 5 minutes interval. There seems to be no default writeout every 5 minutes Regards, Yusuf > > Hi all, > > > > We are observing a consistent interval of about 4 minutes at which there > > are large sustained writes to disk that causes mysqld to block and not > > respond for the entire period. > > > > We are using data=journal with a 128M journal and the filesystem is > > 150GB in size. > > Yep. This is due to some lazy code in ext3. > If the journal fills up, then it flushes the whole journal before > continuing. > > There are three ways to get around this problem. > 1/ fix the code :-) > 2/ use a bigger journal. There is a drawback with bigger journals > though as replay after a crash will take longer. > 3/ Push the bdflush parameters down so that data in the journal will > be flushed out more often and the journal will not get full. > > Something like: > echo 40 0 0 0 60 300 60 0 0 > /proc/sys/vm/bdflush > > The 5th and 6th numbers are significant. > The defaults are 500 and 3000 (hundreths of a second) so > every 5 seconds it flushs data older than 30 seconds. If your > journal cannot hold 30 seconds of data, this is a problem. > So drop the 3000 to maybe 300 or 500 (3 or 5 seconds) and then > drop the 500 to a reasonable fraction of that (50 or so (half a > second)). > > 2 and 3 are complimentary. The bigger the journal, the larger the > age of flushed buffers can be. _______________________________________________ Ext3-users@redhat.com https://listman.redhat.com/mailman/listinfo/ext3-users
