On 17.02.2012 12:51, Bernhard Schrader wrote: > Hi all, > > we just discovered a problem, which I think is related to XFS. Well, > I will try to explain. > > The environment i am working with are around 300 Postgres databases > in separated VM's. All are running with XFS. Differences are just in > kernel versions. > - 2.6.18 > - 2.6.39 > - 3.1.4 > > Some days ago i discovered that the file nodes of my postgresql > tables have strange sizes. They are located in > /var/lib/postgresql/9.0/main/base/[databaseid]/ > If I execute the following commands i get results like this: > > Command: du -sh | tr "\n" " "; du --apparent-size -h > Result: 6.6G . 5.7G . Since a few kernel-version XFS does speculative preallocations, which is primarily a measure to prevent fragmentation. The preallocations should go away when you drop the caches. sync echo 3 > /proc/sys/vm/drop_caches XFS can be prevented to do that with the mount-option "allocsize". Personally i use "allocsize=64k", since i first encountered that behaviour, my workload primarily consists of single-thread writing which doesn't benefit from this preallocation. Your workload OTOH may benefit as it should prevent/lower the fragmentation of the database files. Bis denn -- Real Programmers consider "what you see is what you get" to be just as bad a concept in Text Editors as it is in women. No, the Real Programmer wants a "you asked for it, you got it" text editor -- complicated, cryptic, powerful, unforgiving, dangerous. _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
