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 > > > > _______________________________________________ > Mailing list: https://launchpad.net/~maria-developers > Post to : [email protected] > Unsubscribe : https://launchpad.net/~maria-developers > More help : https://help.launchpad.net/ListHelp _______________________________________________ Mailing list: https://launchpad.net/~maria-developers Post to : [email protected] Unsubscribe : https://launchpad.net/~maria-developers More help : https://help.launchpad.net/ListHelp
