我有一个便宜的 VPS，内存为 128Mb，最大内存为 256Mb。MySQL 启动时会保留大约 110Mb，但实际使用的内存不超过 20Mb。我的 VPS 控制面板显示我使用了 127Mb（我还运行了 nginx 和 sphinx），我知道它显示了保留的内存，但是当我的内存超过 128Mb 时，我的 VPS 每 4 小时会自动重启一次。所以我想强制 MySQL 保留较少的内存。我该怎么做？我对 my.conf 做了一些调整，但效果不大。
顶部输出：
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1 root 15 0 2156 668 572 S 0.0 0.3 0:00.03 init
11311 root 15 0 11212 356 228 S 0.0 0.1 0:00.00 vzctl
11312 root 18 0 3712 1484 1248 S 0.0 0.6 0:00.01 bash
11347 root 18 0 2284 916 732 R 0.0 0.3 0:00.00 top
13978 root 17 -4 2248 552 344 S 0.0 0.2 0:00.00 udevd
14262 root 15 0 1812 564 472 S 0.0 0.2 0:00.03 syslogd
14293 sphinx 15 0 11816 1172 672 S 0.0 0.4 0:00.07 searchd
14305 root 25 0 7192 1036 636 S 0.0 0.4 0:00.00 sshd
14321 root 25 0 2832 836 668 S 0.0 0.3 0:00.00 xinetd
15389 root 18 0 3708 1300 1132 S 0.0 0.5 0:00.00 mysqld_safe
15441 mysql 15 0 113m 16m 4440 S 0.0 6.4 0:00.15 mysqld
15489 root 21 0 13056 1456 340 S 0.0 0.6 0:00.00 nginx
15490 nginx 18 0 13328 2388 992 S 0.0 0.9 0:00.06 nginx
15507 nginx 25 0 19520 5888 4244 S 0.0 2.2 0:00.00 php-cgi
15508 nginx 18 0 19636 4876 2748 S 0.0 1.9 0:00.12 php-cgi
15509 nginx 15 0 19668 4872 2716 S 0.0 1.9 0:00.11 php-cgi
15518 root 18 0 4492 1116 568 S 0.0 0.4 0:00.01 crond
MySQL 调整器：
>> MySQLTuner 1.0.1 - Major Hayden <[email protected]>
>> Bug reports, feature requests, and downloads at http://mysqltuner.com/
>> Run with '--help' for additional options and output filtering
Please enter your MySQL administrative login: root
Please enter your MySQL administrative password:
-------- General Statistics --------------------------------------------------
[--] Skipped version check for MySQLTuner script
[OK] Currently running supported MySQL version 5.0.77
[OK] Operating on 32-bit architecture with less than 2GB RAM
-------- Storage Engine Statistics -------------------------------------------
[--] Status: -Archive -BDB -Federated +InnoDB -ISAM -NDBCluster
[--] Data in InnoDB tables: 1M (Tables: 1)
[OK] Total fragmented tables: 0
-------- Performance Metrics -------------------------------------------------
[--] Up for: 38m 43s (37 q [0.016 qps], 20 conn, TX: 4M, RX: 3K)
[--] Reads / Writes: 100% / 0%
[--] Total buffers: 28.1M global + 832.0K per thread (100 max threads)
[OK] Maximum possible memory usage: 109.4M (42% of installed RAM)
[OK] Slow queries: 0% (0/37)
[OK] Highest usage of available connections: 1% (1/100)
[OK] Key buffer size / total MyISAM indexes: 128.0K/64.0K
[OK] Query cache efficiency: 42.1% (8 cached / 19 selects)
[OK] Query cache prunes per day: 0
[!!] Temporary tables created on disk: 27% (3 on disk / 11 total)
[!!] Thread cache is disabled
[OK] Table cache hit rate: 57% (8 open / 14 opened)
[OK] Open file limit used: 1% (12/1K)
[OK] Table locks acquired immediately: 100% (22 immediate / 22 locks)
[!!] Connections aborted: 10%
[OK] InnoDB data size / buffer pool: 1.5M/8.0M
-------- Recommendations -----------------------------------------------------
General recommendations:
MySQL started within last 24 hours - recommendations may be inaccurate
Enable the slow query log to troubleshoot bad queries
When making adjustments, make tmp_table_size/max_heap_table_size equal
Reduce your SELECT DISTINCT queries without LIMIT clauses
Set thread_cache_size to 4 as a starting value
Your applications are not closing MySQL connections properly
Variables to adjust:
tmp_table_size (> 32M)
max_heap_table_size (> 16M)
thread_cache_size (start at 4)
我认为如果我按照 MySQLtuner 所说的操作，MySQL 将会使用更多的 RAM。
答案1
Linux 上有几种机制可用于严格限制进程可用的内存。
在较新的系统上，您可以使用 cgroups，如果可用的话，这可能是最好的解决方案。（使用包中的工具libcgroup自动将 mysql 守护进程分类到内存控制组或memory.limit_in_bytes = 64M;其他。
在较旧的系统上，如果 mysql 守护进程由脚本启动，您可以简单地使用它ulimit来限制可用的内存 -ulimit -v 65536在脚本中实际启动守护进程的位置上方放置一个语句。
话虽如此，但对于现代软件来说，这确实超出了你的承受范围。你可能只是需要比你拥有的更多的 RAM。一个选择可能是切换到 SQLite 而不是 MySQL — — 那么你根本就不需要运行单独的守护进程了。
答案2
使用调谐引物或者MySQLTuner。
# wget http://mysqltuner.pl/mysqltuner.pl
--2011-01-31 06:49:46-- http://mysqltuner.pl/mysqltuner.pl
Resolving mysqltuner.pl... 174.143.142.58
Connecting to mysqltuner.pl|174.143.142.58|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 39054 (38K) [text/plain]
Saving to: `mysqltuner.pl'
100%[==============================================================================================================================>] 39,054 54.6K/s in 0.7s
2011-01-31 06:49:49 (54.6 KB/s) - `mysqltuner.pl' saved [39054/39054]
# perl mysqltuner.pl
>> MySQLTuner 1.0.1 - Major Hayden <[email protected]>
>> Bug reports, feature requests, and downloads at http://mysqltuner.com/
>> Run with '--help' for additional options and output filtering
Please enter your MySQL administrative login: root
Please enter your MySQL administrative password:
设置 max_connections = 15
128 MB 对于 nginx、php、Sphinx 和 MySQL 来说太少了。
答案3
尽量不要使用 InnoDB，而要使用 MyISAM。添加skip-innodb到 my.cnf 将节省大量内存