> >
> > I would also make sure to check that the hypervisor does write to
> permanent storage before returning to the VM with acknowledgement.
> >
> In the case of ESX, there is no such concern per
> http://kb.vmware.com/kb/1008542.
Very useful info!
> As Heikki commented, VMware recently compared Postgres performance in
> an ESX (5.1) VM versus in a comparable native Linux. We saw 1.
> ESX-level locking causes no vertical scalability degradation, 2.
> Memory oversubscription can indeed be a performance hazard when
> consolidating mulitple Postgres VMs on one host. Yet we found moderate
> memory oversubscription (up to 20%) might work out fine: we saw <5%
> degradation at 20% memory oversubscription in a conventional setup
> (where Postgres server uses 25% memory shared_buffers and VM uses
> out-of-the-box kernel-level memory ballooning.) Nitty-gritty details
> can be found in the whitepaper
> http://www.vmware.com/files/pdf/techpaper/vPostgres-perf.pdf
> (Disclaimer: I'm a author.)
Interesting reading.
There was some earlier comment in this discussion about not using NFS datastores for Postgres VMDK's. Would you think
you'dsee a difference in scalability behavior or performance in these tests if a NFS datastore would be used instead?
Providedthe architecture is properly setup for that, with high speed low latency networking, and fast NAS storage.
Thanks!
> Regards,
> Dong