Friday, 13 April, 2012
It's now over a year when there was a quite interesting exchange with
Vadim and other Percona guys due their TPCC-like benchmark results on
MySQL 5.5 - I've replayed on that time the same tests, but with a better
tuned configuration parameters to demonstrate that with a little bit
more love, MySQL
5.5 may keep TPCC-like workload very well ;-)) However, it was clear
that Adaptive Flushing in 5.5 needs
some improvement (which is now
implemented in 5.6), but there were also several open questions
regarding I/O level and O_DIRECT performance which I was able to clarify
for me only during last
year IO testing on a decent Linux box + storage..
Summarizing all this stuff, you may understand my curiosity to see how well (or not) MySQL 5.6-labs is running today on Percona's TPCC-like workload ;-))
But let's start from the system setup first:
- so, I'm using a 32cores bi-thread Intel box, 128GB RAM
- running Oracle Linux 6.2
- storage: x3 SDD in RAID0
- filesystem: XFS mounted with "noatime,nodiratime,nobarrier,logbufs=8" options
Same TPCC-like workload as before:
- 500W data volume
- 32 concurrent users (initially it was only 16 on the previous tests, but I think it'll be pity to run only 16 users when you have 32cores Linux box ;-))
Then, my first test will be with MySQL 5.5 - even it's GA since more than one year and no any major changes allowed to the code, it was still improved over a time and will give us a good idea about its state for today.. From the previous testing I've retained that to help Adaptive Flushing in 5.5 the "innodb_io_capacity" value should be set to a something huge -- as the algorithm in 5.5 is not following very well the REDO activity, we should avoid to limit it in IO capacity (and when it'll decide to do a big I/O request we should let it happen ;-))
MySQL 5.5 configuration:
table_open_cache = 8000
# perf special
innodb_read_io_threads = 16
innodb_write_io_threads = 16
innodb_io_capacity = 20000
Note that I did not reduce this time the dirty pages percentage to enforce the dirty pages flushing - I'm expecting here that my I/O level will be fast enough to keep the flush activity aligned with REDO logs.. Let's see what is the result now ;-)
MySQL 5.5 results:
- there are some initial QPS drops due critical levels in Checkpoint Age
- but over a time performance become more and more stable, reaching something not far from 110K QPS..
Well, lest move to MySQL 5.6.4 now - it was the last 5.6 release just before 5.6-labs, so Adaptive Flushing was still very similar to what we have in 5.5 (even if some improvement, like page_cleaner thread, were introduced).. So, nothing different within 5.6.4 configuration setup (same 20K IO capacity), except monitoring via METRICS table is enabled.
MySQL 5.6.4 results :
- QPS performance is reaching 160K QPS over a time
- there are more activity drops comparing to 5.5..
- all QPS drops are related to reaching critical levels in Checkpoint Age.. - so it was a time to improve AF here ;-))
- we're reaching near 8000 pages/sec in flushing - good to know to adapt the Max IO capacity in 5.6-labs ;-)
MySQL 5.6-labs configuration:
- same as 5.5, except the following:
- innodb_io_capacity = 4000
- innodb_max_io_capacity = 12000
MySQL 5.6-labs results :
- seems we're unable to flush more than 8000 dirty pages/sec here.. (interesting why?..)
- so, nothing surprising that Checkpoint Age is remaining in critical level most of the time..
- however, there are near no QPS drops at all on the "good" part of graph (up to 11:25 ;-))
- we're reaching 170K QPS now !..
- but after 11:25 there is a huge performance drop.. - why?..
Let's look more in depth:
- the main current InnoDB bottleneck on TPCC-like workload is index lock contention..
- but since 11:25 there is a log_sys mutex contention which is jumping up too!..
- the only reason for log_sys to come in such a configuration is to get REDO log files out of filesystem cache (then on most of REDO I/O writes there will be read-on-write involved, because the REDO I/O operation is not aligned to the filesystem block size..) - this will be fixed soon in 5.6 too ;-)
- however, since I'm using O_DIRECT, and only MySQL is running on my server, what other I/O activity may remove REDO log files from the filesystem cache?...
- from the graph above you may see that "mysqld" process is reaching 128GB memory usage by the end of test..
- of course, when there is no more memory on the system, there is no more place for REDO logs in the filesystem cache either ;-))
- comparing with 5.6.4, seems there was a memory leak bug introduced in 5.6 trunk recently ;-))
- so, I'm happy to find it, but keep it in mind for the moment when trying 5.6-labs on Read+Write workloads - I think it'll be fixed soon..
Well, I'm pretty happy with what I saw.. (except the memory leak bug of course ;-)) -- but I see now the potential we're having under 5.6-labs.. And with all other further improvement which are currently in pipe, MySQL 5.6 should be again yet another the best ever MySQL release after 5.5 !..
Stay tuned.. ;-)
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