Friday, 08 June, 2012
The binlog sync contention was a problem from a long date in MySQL..
Well, it was less visible few years ago until MySQL performance was
quite limited even without binlog enabled ;-)) However, with all latest
performance improvement came with MySQL 5.5 and now with 5.6, it became
unacceptable to see all these excellent goodies simply killed once a
user enabling binlog..
Good news -- the latest MySQL 5.6 labs release is coming with freshly released Binlog Group Commit which is greatly solving this issue. You may find all details about in the Mat's article, while my intention in this post is just to extend little bit already presented benchmark results..
Well, the true performance problem with MySQL binlog is coming not really when it's enabled, but since the "sync_binlog" is set to 1 (means flush binlog to disk on every binlog write).. Usually such a setting is used when user want to avoid any possible data loss (while other value than 1 may be used if it's not a case, and what is curious that setting sync_binlog=100, for ex., may give you the same performance as sync_binlog=0 (means no flush), which may be not far from the initial "base line" performance level).. While setting sync_binlog=1 usually gave you x2-x4 times or more performance regression comparing to the "base line", and the main cost is coming from the number of sync/sec MySQL is doing (as your storage here may be quickly limited in I/O performance). So, the solution with "group commit" is coming naturally here (similar to InnoDB group commit in redo log writes) -- more writes you can group within a single "sync", better performance may be expected. However, as usual, all depends on implementation ;-))
So, what to say about the binlog group commit (BGC) in the latest MySQL 5.6?..
There were many tests executed before BGC became better and better, but I'd like to present you just few ones which attracted my own curiosity ;-)) While on "big" and powerful servers the performance gain was very impressive and pretty easy to obtain, I've also focused on a "small" 12cores server and very modest HDD + SSD config.
- 12cores bi-thread 2900Mhz (small, but really fast), 72GB RAM
- OS: Oracle Linux 6.2
- DATA on x2 HDD, XFS
- REDO and binlog on single SSD, XFS
- binlog OFF
- binlog ON, sync_binlog=0
- binlog ON, sync_binlog=1
- MySQL versions: 5.6.4, 5.6-labs-April, 5.6-labs-June
- Workloads: Sysbench OLTP_RW, dbSTRESS RW-Upd
- Concurrent users: 32
NOTE: I'm testing only 32 concurrent users on this server because a higher load with sync_binlog=1 is hitting overall I/O limits on the storage level, and as well historically 32 users workload was the most "free of internal contentions" :-)
So far, on the following graphs you'll see 3 test cases (binlog OFF, ON, ON+sync_binlog=1) on 3 MySQL versions. Tests were executed sequentially, so you can see 3 tests executed on MySQL 5.6.4, then on 5.6-labs-April, then 5.6-labs-June. And there are also 3 graphs representing by order:
- Adaptive flushing activity (Pages/sec)
- Checkpoint Age in MB
- Executed query/sec (QPS)
Looking on these graphs it's great to see an overall RW performance
improvements coming in MySQL 5.6 over this year:
- 5.6.4 is came with a better RW performance due removed kernel_mutex contention..
- since 5.6-labs-April improved Adaptive Flushing came to the game (and you don't see periodic QPS drops anymore)
- then 5.6-labs-June came with yet more improved Adaptive Flushing (you can see flushing activity more stable now) and Binlog Group Commit -- you can see near x2 times better performance now when sync_binlog=1 !!
- dbSTRESS is representing a more aggressive RW workload, so the BGC impact here is much more important ;-)
- more than x3 times better performance on 5.6-labs-June when sync_binlog=1 now !!
However, what I don't really like in both test workloads is the QPS instability in 5.6-labs-June when sync_binlog=1 -- it may be related to some I/O level limits, or may be some kind of internal contention as well. So, have yet to investigate it later..
Then, of course the picture will be not complete for my curiosity, if I'll not test in the same conditions Percona Server 5.5 which is already integrating a similar solution developed by MariaDB team (MariaDB proposed its own BGC code before MySQL team, and if ideas are similar, implementations are not at all.. - but what about performance?..)
So, I've executed the same tests on Percona Server 5.5 keeping exactly the same config setting except changing adaptive flushing to "keep_average" (which is the best algorithm for this option in XtraDB), and here are the results -- similar graphs, but MySQL 5.6 first, then Percona 5.5 on the same test cases:
- seems like Percona's "keep_average" mode for adaptive flushing is not really working well here.. (and I've also tested "estimate" option -- same result)..
- then, for test case with binlog + sync_binlog=1, we may say here that BGC in MySQL 5.6 is giving the same or better performance vs Percona 5.5
- comparison is similar to the previous test..
- performance with sync_binlog=1 too..
NOTE : I'm intentionally not presenting here any results on more powerful server (32cores or more) as it'll face Percona Server 5.5 to to all performance contentions fixed in MySQL 5.6, which will already make Percona Server way slower even without binlog, so it's out of interest in this scope..
Well, to summarize :
- Binary Group Commit in MySQL 5.6 is looking very promising!
- while I'm still not liking QPS drops observed with sync_binlog=1 ;-)
- NOTE: these QPS drops are not present when more powerful storage is used, so more testing + analyze should be done to fix it generally..
- and, my own pleasure - Adaptive Flushing in MySQL 5.6 seems to work better now than in Percona Server itself, which was the most famous for it until now.. - so I may be only happy with the result of our work in MySQL 5.6 ;-)
Anyway, work is continuing.. ;-)
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