Mysql慢慢地使用内存，直到它开始使用交换。

Question

我正在运行1gb的RAM rackspace数据库服务器。由于某种原因，在大约2天内，内存的使用将从使用非常少的交换变为使用100 to。如果我不重新启动sql，它将继续使用更多的交换。(我的my.cnf文件如下所示，内存使用情况如下所示)

一些背景:我有大约50个活动数据库，它们的模式与使用INNODB的表相同。我有几个使用MyISAM的流量很少的数据库。

在INNODB表上，我不使用持久连接。我还有一个创建临时表的报告函数。(这可能是资源密集型的，但并不经常发生)

我使用CENTOS 6.3和mysql 5.5.28-log

即使我正在使用交换，性能仍然相当不错。我只是担心如果我不每隔几天重启一次，我就会有问题。

这是我的大约2天的免费-m日志：(第一个记录是在mysql重新启动之后)

12/26 2:08 PM EST
             total       used       free     shared    buffers     cached
Mem:           992        697        295          0         74        362
-/+ buffers/cache:        260        732
Swap:          976         15        961

12/26 4:10 PM EST
[root@php-pos-db ~]# free -m
             total       used       free     shared    buffers     cached
Mem:           992        791        201          0         97        405
-/+ buffers/cache:        287        705
Swap:          976         14        961

12/27 2:52 PM EST
[root@php-pos-db ~]# free -m
             total       used       free     shared    buffers     cached
Mem:           992        947         45          0         55        169
-/+ buffers/cache:        722        270
Swap:          976         34        942

12/28 1:41 PM EST
             total       used       free     shared    buffers     cached
Mem:           992        963         29          0         45        119
-/+ buffers/cache:        797        195
Swap:          976         48        927

12/28 7:24 PM EST
[root@php-pos-db ~]# free -m
             total       used       free     shared    buffers     cached
Mem:           992        957         35          0         41        141
-/+ buffers/cache:        774        218
Swap:          976         90        886

12/28 8:33 PM EST
[root@php-pos-db ~]# free -m
             total       used       free     shared    buffers     cached
Mem:           992        948         44          0         48        130
-/+ buffers/cache:        768        224
Swap:          976         96        880

my.cnf

# The MySQL database server configuration file.
#
# You can copy this to one of:
# - "/etc/mysql/my.cnf" to set global options,
# - "~/.my.cnf" to set user-specific options.
# 
# One can use all long options that the program supports.
# Run program with --help to get a list of available options and with
# --print-defaults to see which it would actually understand and use.
#
# For explanations see
# http://dev.mysql.com/doc/refman/5.1/en/server-system-variables.html
#
# Take care to only add/remove/change a setting if you are comfortable
# doing so! For Rackspace customers, if you have any questions or
# concerns, please contact the MySQL Database Services Team. Be aware
# that some work performed by this team can involve additional billable
# fees.
#
# This file generated for host php-pos-db please modify
# variables if the server is resized from 1016636kB

[mysqld]

### General
user                = mysql
port                = 3306
datadir                         = /var/lib/mysql
tmpdir                          = /tmp
socket                          = /var/lib/mysql/mysql.sock
skip-external-locking           = 1
log_error                       = /var/log/mysqld.log

## This prevents using host-based authentication. That means users must be
## created using an ip-address (ie 'myuser'@'192.168.100.1') or must make
## use of the % wildcard (ie 'myuser'@'%'). The benefit to not using
## host-based authentication is that DNS will not impact MySQL performance.
#skip-name-resolve

## If open-files-limit is set very low, MySQL may increase on its own. Either
## way, increase this if MySQL gives 'too many open files' errors. Setting
## this above 65535 could be unwise (MySQL may crash).
open-files-limit                = 20000

### Cache
thread-cache-size               = 16
table-open-cache                = 4096
table-definition-cache          = 512

## Generally, it is unwise to set the query cache to be larger than 64-128M 
## as the costs associated with maintaining the cache outweigh the performance
## gains. A far superior solution would be to implement memcached, though this
## required modifying the application, among other things.
query-cache-type                = 1
query-cache-size                = 32M
query-cache-limit               = 1M

### Per-thread Buffers
sort-buffer-size                = 1M
read-buffer-size                = 1M
read-rnd-buffer-size            = 2M
join-buffer-size                = 1M

### Temp Tables
tmp-table-size                  = 64M 
max-heap-table-size             = 64M

### Networking
back-log                        = 100
max-connections                 = 50
max-connect-errors              = 10000
max-allowed-packet              = 16M
interactive-timeout             = 600
wait-timeout                    = 180
net_read_timeout        = 30
net_write_timeout       = 30
# This value is the size of the listen queue for incoming TCP/IP connections.
back_log            = 128

#### Storage Engines
## Set this to force MySQL to use a particular engine / table-type
## for new tables. This setting can still be overridden by specifying
## the engine explicitly in the CREATE TABLE statement.
default-storage-engine         = InnoDB

## Makes sure MySQL does not start if InnoDB fails to start. This helps
## prevent ugly silent failures.
innodb                          = FORCE

### MyISAM
## Not sure what to set this to?
## Try running a 'du -sch /var/lib/mysql/*/*.MYI'
## This will give you a good estimate on the size of all the MyISAM indexes.
## (The buffer may not need to set that high, however)
key-buffer-size                 = 2M
## This setting controls the size of the buffer that is allocated when 
## sorting MyISAM indexes during a REPAIR TABLE or when creating indexes 
## with CREATE INDEX or ALTER TABLE.
myisam-sort-buffer-size         = 2M

### InnoDB
## Note: While most settings in MySQL can be set at run-time, many InnoDB
## variables cannot be set at runtime as require restarting MySQL
###
## These settings control how much RAM InnoDB will use. Generally, when using
## mostly InnoDB tables, the innodb-buffer-pool-size should be as large as
## is possible without swapping or starving other processes of RAM. The other 
## two settings usually do not need to be changed, but can help for very large 
## datasets.
innodb-buffer-pool-size         = 285M
innodb-log-buffer-size          = 8M

## Be careful when changing these as they require re-generating the 
## ib-logfile* files, which must be done carefully. Do not change this unless 
## you are familiar with the procedure.
innodb-log-file-size           = 128M
innodb-log-files-in-group      = 2

## This will cause each table to create its own .ibd file
innodb-file-per-table           = 1

## Setting this to 2 will decrease disk I/O but can cause up to a second of
## queries to be lost during a hard outage (i.e. power failures)
# innodb-flush-log-at-trx-commit = 2

### Replication
## Set this to the Server's instance ID in replication environments
server-id                       = 1

#log-bin                        = /var/lib/mysql/bin-log
#relay-log                      = /var/lib/mysql/relay-log
#relay-log-space-limit          = 4G
#expire-logs-days               = 5

## This should be enabled on conventional MySQL slaves
#read-only                      = 1

## This will cause replicated statements on a slave to be written to the slave's binlog
## Enable this on the middle slave of M->S->S configs
#log-slave-updates              = 1

#binlog-format                  = STATEMENT

### Logging
## This option determines the destination for general query log and slow query log output.
## The option value can be given as one or more of the words TABLE, FILE, or NONE.
## NOTE: Table logging takes away 50% of performance and thus is not recommended
##       http://bugs.mysql.com/bug.php?id=30414
## In addition, you cannot backup the contents of these tables properly
## (mysqldump skips these tables by default since they cannot be locked)
#log-output                     = FILE
slow-query-log                 = 1
slow-query-log-file            = /var/lib/mysql/slow-log
long-query-time                = 2
log-queries-not-using-indexes  = 1

[mysqld-safe]
log-error                       = /var/log/mysqld.log

[mysqldump]
max-allowed-packet      = 16M

# * IMPORTANT: Additional settings that can override those from this file!
#   The files must end with '.cnf', otherwise they'll be ignored.
#
!includedir /etc/sysconfig/mysqld-config/

Answer 1

MySQL确实有一个坏习惯，那就是交换快乐。杰里米·科尔最好在他的博客：http://blog.jcole.us/2012/04/16/a-brief-update-on-numa-and-mysql/中提到这一点。从这个博客中，您了解到您可以做一些事情:在/etc/init.d/mysql中添加numactl --interleave=all。

建议

如果服务器只用于执行MySQL，请在/etc/my.cnf中更改以下内容：

[mysqld]
innodb_open_files=1000
innodb_flush_method=O_DIRECT
innodb_buffer_pool_size=768M
innodb_log_file_size=192M

如果服务器至少是双核，则添加以下内容

innodb_buffer_pool_instances=2
innodb_read_io_threads=16
innodb_write_io_threads=16
innodb_io_capacity=2000

接下来，登录到mysql运行SET GLOBAL innodb_fast_shutdown = 0;

接下来，在操作系统中运行以下命令

cd /var/lib/mysql
service mysql stop
mv ib_logfile0 ib_logfile0.bak
mv ib_logfile1 ib_logfile1.bak
service mysql start

试试看!！

更新2012-12-31 08:30东部时间

从你最后的评论

它停止了大约1 gb的爬升。我删除了未使用的数据库，看起来MySQL5.5在内存中存储了大量数据，因为在5.0中没有发生这种情况。mysql改变了很多吗？

是的，MySQL改变了很多。事实上，在许多情况下，从MySQL 5.0升级到MySQL 5.5会导致性能下降。InnoDB 5.5现在已经具备了进行超线程和多核协作的能力。

珀科纳在一段时间前对此进行了测试。。

请给我读一下过去关于这个问题的文章

• Jul 16, 2012：从mysql服务器5.0迁移到5.5时存储过程性能下降
• Nov 24, 2011：为什么MySQL5.5比5.1慢(linux，使用mysqlslap)
• Oct 05, 2011：查询在一些较新的MySQL版本中运行很长时间
• Sep 20, 2011：多核与MySQL性能
• Jun 19, 2011：如何正确地执行MySQL烘焙？

我还在ServerFault和StackOverflow上写过这方面的文章

• Feb 22, 2012：https://serverfault.com/questions/362388/mysql-5-1-vs-mysql-5-5-5-1-twice-as-fast/362706#362706
• Feb 08, 2012：https://stackoverflow.com/questions/9202825/mysql-5-5-perfomance/9202860#9202860

Answer 2

除了Rolando给出的非常好的建议之外，您还可以在系统方面使用sysctl激活无交换设置。我通常将vm.swappiness=10设置在/etc/sysctl.conf中的MySQL机器上。它允许对交换空间的访问受到限制，但如果需要，则允许使用。

vm.swappiness的默认值是60，这是非常允许的。