On 06/24/2014 03:45 AM, Mark Kirkwood wrote:
On 24/06/14 18:15, Robert van Leeuwen wrote:
All of which means that Mysql performance (looking at you binlog) may
still suffer due to lots of small block size sync writes.
Which begs the question:
Anyone running a reasonable busy Mysql server on Ceph backed storage?
We tried and it did not perform good enough.
We have a small ceph cluster: 3 machines with 2 SSD journals and 10
spinning disks each.
Using ceph trough kvm rbd we were seeing performance equal to about
1-2 spinning disks.
Reading this thread it now looks a bit if there are inherent
architecture + latency issues that would prevent it from performing
great as a Mysql database store.
I'd be interested in example setups where people are running busy
databases on Ceph backed volumes.
Yes indeed,
We have looked extensively at Postgres performance on rbd - and while it
is not Mysql, the underlying mechanism for durable writes (i.e commit)
is essentially very similar (fsync, fdatasync and friends). We achieved
quite reasonable performance (by that I mean sufficiently encouraging to
be happy to host real datastores for our moderately busy systems - and
we are continuing to investigate using it for our really busy ones).
I have not experimented exptensively with the various choices of flush
method (called sync method in Postgres but the same idea), as we found
quite good performance with the default (fdatasync). However this is
clearly an area that is worth investigation.
FWIW, I ran through the DBT-3 benchmark suite on MariaDB ontop of
qemu/kvm RBD with a 3X replication pool on 30 OSDs with 3x replication.
I kept buffer sizes small to try to force disk IO and benchmarked
against a local disk passed through to the VM. We typically did about
3-4x faster on queries than the local disk, but there were a couple of
queries were we were slower. I didn't look at how multiple databases
scaled though. That may have it's own benefits and challenges.
I'm encouraged overall though. It looks like from your comments and
from my own testing it's possible to have at least passable performance
with a single database and potentially as we reduce latency in Ceph make
it even better. With multiple databases, it's entirely possible that we
can do pretty good even now.
Regards
Mark
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