Kage, The main advantage is gained by avoiding I/O through the virtual disk. The layout of the virtual disk tends to turn most I/O into random I/O, even I/O that starts as sequential. The factor of 10 performance difference between random/sequential I/O causes the majority of the performance problem. I have not had personal experience with using an NFS mount point to run a database so I cannot really comment on that. Good luck with your evaluation.
Cheers, Ken On Tue, Jul 28, 2009 at 04:12:55PM -0400, Kage wrote: > (didn't do a reply-all, sorry if you get this twice, Ken) > > What, if any, performance gains exist by using an NFS mountpoint for > the Postgres database within a virtual machine? ?In this case, I/O is > not directly placed on the virtual disk (unless the actual "act" of > I/O itself, regardless of what is being acted upon (virtual disk or > not), is also an issue). ?Could this potentially yield any performance > increase? > > Also, no, I have not tried MySQL yet with our RT setup. ?I'd like to > move our database to MySQL to do some testing with that and gather > realistic metrics of "here's our data in Postgres vs. MySQL". > > On Tue, Jul 28, 2009 at 3:51 PM, Kenneth Marshall<[email protected]> wrote: > > On Tue, Jul 28, 2009 at 03:35:12PM -0400, Kage wrote: > >> Well, basically, Postgres is seemingly a bucket of fail specifically > >> for the RT system I maintain. ?We run RT/Postgres on a Ubuntu Hardy > >> LTS virtual machine running 2 virtual CPUs and the KVM maximum of 2GB > >> RAM, but Postgres ends up using so much in resources that it actually > >> kills the entire KVM system on the virtual host. ?I know tuning of > >> Postgres can fix this, but we've experienced issues with Postgres on > >> many other virtual machines, leading us to believe that it may simply > >> be an issue with Postgres not getting along well with KVM (which is a > >> somewhat known issue). ?Ideally, I want to migrate my RT database from > >> Postgres to MySQL, and preserve ALL data (tickets, attachments, links, > >> everything). ?Is there an "guaranteed to work" method to do this that > >> anyone knows of? ?Thanks! > >> > >> Specs: > >> Postgres: 8.3 > >> RT: 3.6.5 > >> MySQL candidate on Hardy: 5.0.51a-3ubuntu5.4 > >> > >> Any help would be greatly appreciated. ?Thanks! > >> > >> -- > >> ~ Kage > >> http://vitund.com > >> http://hackthissite.org > > > > Hi Kage, > > > > I have had trouble with VMs with any I/O bound system. Have you > > tested your system with MySQL? You may just be swapping one I/O > > problem for another. That being said, for anything but the most > > trivial of DBs, tuning your backend DB be it PostgreSQL, MySQL, > > Oracle,... is critical for getting good performance. > > > > Another data point, I have had a simple repeated file read of a > > DNS zone file for an XFER tank a VM. VMs work well for CPU intensive > > tasks with small amount of I/O. For any larger amount of I/O, using > > real storage is a must. Good luck with whichever backend you choose. > > A big plus for both the Oracle and PostgreSQL backend is the > > availability of full-text indexing which allows content and attachment > > searches to use an index and not take your DB with a full table scan. > > > > Regards, > > Ken > > -- > ~ Kage > http://vitund.com > http://hackthissite.org > _______________________________________________ http://lists.bestpractical.com/cgi-bin/mailman/listinfo/rt-users Community help: http://wiki.bestpractical.com Commercial support: [email protected] Discover RT's hidden secrets with RT Essentials from O'Reilly Media. Buy a copy at http://rtbook.bestpractical.com
