maria-developers team mailing list archive

[Sergey Vojtovich <svoj@xxxxxxxxxxx>]

Hi Sergei,

MySQL has the following optimization: WL#5772 - Add partitioned Table
Definition Cache to avoid using LOCK_open and its derivatives in DML queries.

We didn't agree with it and implemented it differently:
MDEV-4702 - Reduce usage of LOCK_open. It was a major rewrite of table cache
which improved things considerably, but we didn't reach MySQL numbers yet.

We need to do a few extra minor things to get closer to MySQL numbers,
MDEV-4956 - Reduce usage of LOCK_open: TABLE_SHARE::tdc.used_tables is among of
them (patch is ready).

Regards,
Sergey

On Thu, Nov 21, 2013 at 10:01:35PM +0400, Sergei Petrunia wrote:
> On Thu, Nov 21, 2013 at 06:32:45PM +0100, Axel Schwenke wrote:
> > I have run another sysbench with in-memory workload to check where we are
> > with respect to mutex contention.
> > 
> Great to see the results!
> 
> > The benchmark is sysbench OLTP (using the bzr trunk of sysbench with LUA
> > support). 10 mio rows in a single table (about 2.5G .ibd file). InnoDB
> > buffer pool set to 32G and warmed up.
> > 
> > I have run the test on two different machines. First on our old trusty
> > facebook2 machine with 8 cores/16 threads in two NUMA zones. Second on the
> > fat lizard2 machine with 32 cores/64 threads in 4 NUMA zones.
> > 
> > As expected, the heavy contention of the LOCK_open mutex is more visible on
> > the bigger machine (I have not done any detailed analysis in this benchmark,
> > but before while doing benchmarks for MDEV-5081)
> > 
> > I notice a visible performance gain in MariaDB-10.0 over MariaDB-5.5 at 32
> > threads. This is probably due to the work on the InnoDB kernel mutex
> > (impossible to prove since 5.5 doesn't have mutex instrumentation). At
> > higher concurrency however the LOCK_open mutex kicks in and performance is
> > clearly dominated by that mutex alone (it flattens out for all 5.5 and 10.0
> > versions of MariaDB)
> >
> MySQL 5.6 clearly outperforms MariaDB on 32 cores. Do we know - Is this because 
> 5.6 has some optimization to LOCK_open (can anybody point at a patch or WL
> number?) , and that optimization hasn't been ported to 10.0?
> > 
> > The good news is, that 10.0.4, 10.0.5 and 10.0.6 are quite close. There is a
> > small regression from 10.0.4 to 10.0.5, but IMHO this isn't worth
> > investigation while the LOCK_open issue is not fixed.
> > 
> > Attached: diagrams. OpenOffice spreadsheets.
> > 
> Thanks a lot for doing this!
> 
> BR
>  Sergei
> -- 
> Sergei Petrunia, Software Developer
> MariaDB | Skype: sergefp | Blog: http://s.petrunia.net/blog
> 
> 
> 
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