MySQL MyISAM performance tuning on T2000
By yufei on Aug 07, 2006
The default storage engine of MySQL is MyISAM. Unlike InnoDB, it stores each MyISAM table in three files, the schema file(.frm), the data file(.MYD) and the index file(.MYI). It only supports filesystem. It does table level locking.
Compared to InnoDB, MyISAM doesn't have its own data buffer cache, it only has index buffer cache, the key buffer (variable
key_buffer_size). We need to use file system buffer cache for data cache for MyISAM tables.
Here are a few steps of how to tune MySQL MyISAM performance on T2000 or other Solaris platforms
There is a very good performance feature in MySQL 5.1 beta that allows MyISAM using mmap memory instead of malloced buffers. If you experienced very high mutex contention in earlier MySQL releases, you can get a huge performance improvments. How do you know if you have this problem?
- If you are using MySQL 5.0 or earlier version, during the test
you can collect "lockstat sleep 1" and if you see ufs_lockfs_begin and
ufs_lockfs_end in the callers column.
You are likely to get the performance boost by going to the latest 5.1.
You need to have "myisam_use_mmap=1"
in /etc/my.cnf to be able to use this feature. This is an example of
lockstat output that has the performance issue.
Adaptive mutex spin: 140294 events in 1.145 seconds (122505 events/sec)
Count indv cuml rcnt spin Lock Caller
31341 22% 22% 0.00 9 0x600052c4d10 ufs_lockfs_end+0x70
30952 22% 44% 0.00 10 0x600052c4d10 ufs_lockfs_begin+0xe4
- You can use libumem or libmtmalloc to get scalable memory allocation performance on multi-threaded MySQL. The way to do this is before mysql is started, setenv LD_PRELOAD_64 /usr/lib/sparcv9/libumem.so. This example is for 64bit MySQL. For 32bit MySQL you can do setenv LD_PRELOAD /usr/lib/libumem.so
- Since we have to use filesystem buffer cache to cache data for MyISAM tables, it is important to tune segmap_percent in /etc/system. The default segmap_percent is 12% on solaris, that means you can only get to use 12% of the system memory for filesystem buffer cache. It depends on your database size, but setting it too high could lead low memory on the system causing excessive paging. In our case, we set it to 80%. In /etc/system, set segmap_percent=80. You need to reboot the system to make it effective.
cache is important feature for MyISAM to cache index blocks
that allows multiple threads to access key buffer simultaneously. You
can check the performance of key cache by doing "show status" and look
at what is the ratio of key_reads and key_read_requests. It should be
less than 1%. Otherwise, you might need to increase
key_buffer_size. The maximum for key_buffer_size is 4G however you can
create multiple key cache (The size limit of 4GB applies to each cache
individually, not as a group.) That will also help on the situation
where access to one key cache structure does not block access to the
other key cache
- Making sure there is no io bottleneck. Collect "iostat -xtcnz 5" on the system and
look at that what is the disk response time (column asvc_t in
milliseconds) and what is the average outstanding ios(column actv).
- On solaris systems, you can use "prstat
-Lmc" to monitor the active processes on the systems.