Re: Mysql performance on CephFS vs RBD

[RDS <rs350z@xxxxxx>]

There is 1 more thing that I noticed when using cephfs instead of RBD for MySQL, and that is CPU usage on the client.

When using RBD, I was using 99% of the CPU’s. When I switched to cephfs, the same tests were using 60% of the CPU. Performance was about equal. This test was an OLTP sysbench using 8 tables with 8 concurrent jobs all using the same pool.

On May 1, 2017, at 12:26 PM, Gregory Farnum <gfarnum@xxxxxxxxxx> wrote:

On Mon, May 1, 2017 at 9:17 AM, Babu Shanmugam <babu@xxxxxxxx> wrote:

My intention is to just identify the root cause for the too much time spent on a "table create" operation on CephFS. I am *not* trying to benchmark with my testing. Sorry if it wasn't clear in my mail.

I am sure the time spent would be lesser if I had a proper CEPH setup. But, I believe even then, the "Table create" operation takes more time in CephFS than RBD. Please correct me if I am wrong.

As your data shows, fsync is just much slower on CephFS. I think you'd
find the difference was less on a real cluster, but it's always going
to be slower than RBD is — an fsync requires committing metadata
updates, and that requires the client sending a message to the MDS
which then commits to RADOS, PLUS the client sending out its own data
directly to RADOS. In comparison, RBD is just talking to OSDs
directly, and often enough an fsync will only require one message (or
more commonly two in parallel?) so it's going to perform better no
matter how much stuff gets optimized. *shrug*
-Greg
_______________________________________________
ceph-users mailing list
ceph-users@xxxxxxxxxxxxxx
http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com

Rick Stehno

_______________________________________________
ceph-users mailing list
ceph-users@xxxxxxxxxxxxxx
http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com