Centos运行Mysql因为内存不足进程被杀

今天刚刚申请了一个新的域名，在申请完域名刚准备绑定给小伙伴分享注册新域名的喜悦时，刚把网站发到我们小伙伴们的讨论群里，却发现访问不了了，提示，数据库连接失败！

真的时一个尴尬.....    所有人都进不了我的网站，然后登录centos后台，发现了这样的提示

out of memory !  Kill   process (Mysqld)  我英语未过四级，但是这个简单英文还是能看懂的，大致意思时内存不够了，然后把mysql的进程给杀掉了，阿西吧！！！

尴尬了，怎么办？  小伙伴们不能让我太尴尬啊，所以给我提了建议，说可以通过修改mysql的配置文件my.ini实现降低mysql的运行所占用内容。

然后找了资料，有一片就不错的文章，在这里就不造轮子重写了，在此转载过来，同时表示谢意。

1G 内存如何优化mysql

文章内容如下：  供大家参考

 

同时在线访问量继续增大 对于1G 内存的服务器明显感觉到吃力  严重时甚至每天都会死机 或者时不时的服务器卡一下 这个问题曾经困扰了我 

半个多月  MySQL 使用是很具伸缩性的算法，因此你通常能用很少的内存运行或给MySQL更 多的被存以得到更好的性能。 

安装好mysql 后，配制文件应该在/usr/local/mysql/share/mysql 目录中，配  制文件有几个，有my-huge.cnf、 my-medium.cnf、my-large.cnf、my-small.cnf,不同的流量的网站和不同配制的服  务器环境，当然需要有不同的  配制文件了。一般的情况下，my-medium.cnf 这个配制文件就能满足我们的大多 需要； 

一般我们会把配置文件拷贝到/etc/my.cnf 只需要修改这个配置文件就可以了  使用mysqladmin variables extended-status –u root –p 可以看到目前的 

参数  有３个配置参数是最重要的，即 

key_buffer_size,query_cache_size,table_cache

1.key_buffer_size

key_buffer_size 只对MyISAM 表起作用

key_buffer_size 指定索引缓冲区的大小，它决定索引处理的速度，尤其是索引  读的速度。一般我们设为16M,实  际上稍微大一点的站点 这个数字是远远不够的，通过检查状态值 Key_read_requests 和 Key_reads,可以知道key_buffer_size 设置是否合理。比例key_reads/ key_read_requests 应该尽可  能的低，至少是1:100，1:1000 更好（上述状态值可以使用SHOW STATUS LIKE' key_read%'获得）。 或者如 果你装了phpmyadmin可以通过服务器运行状态看到,笔者推荐用phpmyadmin管 理mysql，以下的状态值都是本人 通过phpmyadmin 获得的。

实例分析:

这个服务器已经运行了20 天

key_buffer_size – 128M

key_read_requests – 650759289

key_reads - 79112

比例接近1:8000 健康状况非常好 , 另外一个估计key_buffer_size 的办法 把你网站数据库的每个表的索引所占 空间大小加起来看看 

以此服务器为例:比较大的几个表索引加起来大概125M 这个数字会随着表变大  而变大 

2.query_cache_size

从4.0.1 开始，MySQL 提供了查询缓冲机制。使用查询缓冲，MySQL 将SELECT  语句和查询结果存放在缓冲区中，今 后对于同样的SELECT 语句（区分大小写），将直接从缓冲区中读取结果。根据 MySQL 用户手册，使用查询缓冲最 多可以达到238%的效率. 通过调节以下几个参数可以知道query_cache_size 设置得是否合理 

Qcache inserts

Qcache hits

Qcache lowmem prunes

Qcache free blocks

Qcache total blocks

Qcache_lowmem_prunes 的值非常大，则表明经常出现缓冲不够的情况,同时  Qcache_hits 的值非常大，则表明查 询缓冲使用非常频繁，此时需要增加缓冲大小 

Qcache_hits 的值不大，则表明你的查询重复率很低，这种情况下使用查询缓冲 反而会影响效率，那么可以考虑 不用查询缓冲。此外，在SELECT 语句中加入SQL_NO_CACHE 可以明确表示不使用 查询缓冲。 

Qcache_free_blocks，如果该值非常大，则表明缓冲区中碎片很多

query_cache_type 指定是否使用查询缓冲

我设置:

query_cache_size = 32M

query_cache_type= 1

得到如下状态值:

Qcache queries in cache 12737 表明目前缓存的条数

Qcache inserts 20649006

Qcache hits 79060095 看来重复查询率还挺高的

Qcache lowmem prunes 617913 有这么多次出现缓存过低的情况

Qcache not cached 189896

Qcache free memory 18573912 目前剩余缓存空间

Qcache free blocks 5328 这个数字似乎有点大 碎片不少

Qcache total blocks 30953

如果内存允许32M 应该要往上加点

3.table_cache

table_cache 指定表高速缓存的大小。每当MySQL 访问一个表时，如果在表缓冲  区中还有空间，该表就被打开并 放入其中，这样可以更快地访问表内容。通过检查峰值时间的状态值 

Open_tables 和Opened_tables，可以决定  是否需要增加table_cache 的值。如果你发现open_tables 等于table_cache， 并且opened_tables 在不断增长， 那么你就需要增加table_cache 的值了（上述状态值可以使用SHOW STATUS LIKE' Open%tables'获得）。注意 ，不能盲目地把table_cache 设置成很大的值。如果设置得太高，可能会造成文 件描述符不足，从而造成性能不  稳定或者连接失败。 对于有1G 内存的机器，推荐值是128－256。 

笔者设置table_cache = 256

得到以下状态:

Open tables 256

Opened tables 9046

虽然open_tables 已经等于table_cache，但是相对于服务器运行时间来说,已  经运行了20 天，opened_tables 的 值也非常低。因此，增加table_cache 的值应该用处不大。 如果运行了6 个小时就出现上述值 那就要考虑增大table_cache 

4.log-bin

如果你不需要记录2 进制log 就把这个功能关掉,注意关掉以后就不能恢复出问  题前的数据了，需要您手动备份 ，二进制日志包含所有更新数据的语句，其目的是在恢复数据库时用它来把数据

尽可能恢复到最后的状态。另  外，如果做同步复制( Replication )的话，也需要使用二进制日志传送修改情 况。  log_bin 指定日志文件，如果不提供文件名，MySQL 将自己产生缺省文件名。MySQL 会在文件名后面自动添加数 字引，每次启动服务时，都会重新生成一个新的二进制文件。 此外，使用log-bin-index 可以指定索引文件；使用binlog-do-db 可以指定记 

录的数据库；使用binlogignore-  db 可以指定不记录的数据库。注意的是：binlog-do-db和 binlog-ignore-db 一次只指定一个数据库，指 定多个数据库需要多个语句。而且，MySQL会将所有的数据库名称改成小写，在 指定数据库时必须全部使用小写 名字，否则不会起作用。 

关掉这个功能只需要在他前面加上#号

#log-bin

5.开启慢查询日志( slow query log )

慢查询日志对于跟踪有问题的查询非常有用。它记录所有查过long_query_time  的查询，如果需要，还可以记 录不使用索引的记录。下面是一个慢查询日志的例子： 

开启慢查询日志，需要设置参数log_slow_queries、long_query_times、

log-queries-not-using-indexes。

log_slow_queries 指定日志文件，如果不提供文件名，MySQL 将自己产生缺省文  件名。long_query_times 指定慢 查询的阈值，缺省是10 秒。log-queries-not-using-indexes 是4.1.0 以后引 入的参数，它指示记录不使用索引 的查询。 

笔者设置long_query_time=10

6.其他一些重要参数

笔者设置:

sort_buffer_size = 1M

max_connections=120

wait_timeout =120

back_log=100

read_buffer_size = 1M

thread_cache=32

interactive_timeout=120

thread_concurrency = 4

参数说明:

back_log

要求MySQL 能有的连接数量。当主要MySQL 线程在一个很短时间内得到非常多的  连接请求，这就起作用，然后 主线程花些时间(尽管很短)检查连接并且启动一个新线程。back_log 值指出在 MySQL 暂时停止回答新请求之前的 短时间内多少个请求可以被存在堆栈中。只有如果期望在一个短时间内有很多连 接，你需要增加它，换句话说 ，这值对到来的TCP/IP 连接的侦听队列的大小。你的操作系统在这个队列大小 上有它自己的限制。  检查你的OS 文档找出这个变量 的最大值。试图设定back_log 高 于你的操作系统的限制将是无效的。 

max_connections

并发连接数目最大，120 超过这个值就会自动恢复，出了问题能自动解决

thread_cache

没找到具体说明，不过设置为32 后 20 天才创建了400 多个线程 而以前一天就  创建了上千个线程所以还是有 用的 

thread_concurrency

#设置为你的cpu 数目x2,例如，只有一个cpu,那么thread_concurrency=2

#有2 个cpu,那么thread_concurrency=4

skip-innodb

#去掉innodb 支持

附my.cnf 全部文件

[sql]  view plain  copy

 

 # Example MySQL config file for medium systems.
 #
 # This is for a system with little memory (32M - 64M) where MySQL plays
 # an important part, or systems up to 128M where MySQL is used together
 with
 # other programs (such as a web server)
 directory is /var/lib/mysql) or
 # ~/.my.cnf to set user-specific options.
 #
 # In this file, you can use all long options that a program supports.
 # If you want to know which options a program supports, run the program
 # with the "--help" option.
 # The following options will be passed to all MySQL clients
 [client]
 #password = your_password
 port = 3306
 socket = /tmp/mysql.sock
 #socket = /var/lib/mysql/mysql.sock
 # Here follows entries for some specific programs
 # The MySQL server
 [mysqld]
 port = 3306
 socket = /tmp/mysql.sock
 #socket = /var/lib/mysql/mysql.sock
 skip-locking
 key_buffer = 128M
 max_allowed_packet = 1M
 table_cache = 256
 sort_buffer_size = 1M
 net_buffer_length = 16K
 myisam_sort_buffer_size = 1M
 max_connections=120
 #addnew config
 wait_timeout =120
 back_log=100
 read_buffer_size = 1M
 thread_cache=32
 skip-innodb
 skip-bdb
 skip-name-resolve
 join_buffer_size=512k
 query_cache_size = 32M
 interactive_timeout=120
 long_query_time=10
 TCP/IP port at all. This can be a security enhancement,
 # if all processes that need to connect to mysqld run on the same host.
 # All interaction with mysqld must be made via Unix sockets or named pipes.
 # Note that using this option without enabling named pipes on Windows
 # (via the "enable-named-pipe" option) will render mysqld useless!
 #
 #skip-networking
 # Replication Master Server (default)
 # binary logging is required for replication
 #log-bin
 # required unique id between 1 and 2^32 - 1
 # defaults to 1 if master-host is not set
 # but will not function as a master if omitted
 server-id = 1
 # Replication Slave (comment out master section to use this)
 #
 # To configure this host as a replication slave, you can choose between
 # two methods :
 #
 # 1) Use the CHANGE MASTER TO command (fully described in our manual) -
 # the syntax is:
 #
 # CHANGE MASTER TO MASTER_HOST=, MASTER_PORT= ,
 # MASTER_USER=, MASTER_PASSWORD= ;
 #
 # where you replace , , by quoted strings and
 # by the master's port number (3306 by default).
 #
 # Example:
 #
 # CHANGE MASTER TO MASTER_HOST='125.564.12.1', MASTER_PORT=3306,
 # MASTER_USER='joe', MASTER_PASSWORD='secret';
 #
 # OR
 #
 # 2) Set the variables below. However, in case you choose this method,
 then
 # start replication for the first time (even unsuccessfully, for example
 # if you mistyped the password in master-password and the slave fails to
 # connect), the slave will create a master.info file, and any later
 # change in this file to the variables' values below will be ignored and
 # overridden by the content of the master.info file, unless you shutdown
 # the slave server, delete master.info and restart the slaver server.
 # For that reason, you may want to leave the lines below untouched
 # (commented) and instead use CHANGE MASTER TO (see above)
 #
 # required unique id between 2 and 2^32 - 1
 # (and different from the master)
 # defaults to 2 if master-host is set
 # but will not function as a slave if omitted
 #server-id = 2
 #
 # The replication master for this slave - required
 #master-host =
 #
 # The username the slave will use for authentication when connecting
 # to the master - required
 #master-user =
 #
 # The password the slave will authenticate with when connecting to
 # the master - required
 #master-password =
 #
 # The port the master is listening on.
 # optional - defaults to 3306
 #master-port =
 #
 # binary logging - not required for slaves, but recommended
 #log-bin
 # Point the following paths to different dedicated disks
 #tmpdir = /tmp/
 #log-update = /path-to-dedicated-directory/hostname
 # Uncomment the following if you are using BDB tables
 #bdb_cache_size = 4M
 #bdb_max_lock = 10000
 # Uncomment the following if you are using InnoDB tables
 #innodb_log_buffer_size = 8M
 #innodb_flush_log_at_trx_commit = 1
 #innodb_lock_wait_timeout = 50
 [mysqldump]
 quick
 max_allowed_packet = 16M
 [mysql]
 no-auto-rehash
 # Remove the next comment character if you are not familiar with SQL
 #safe-updates
 [isamchk]
 key_buffer = 20M
 sort_buffer_size = 20M
 read_buffer = 2M
 write_buffer = 2M
 [myisamchk]
 key_buffer = 20M
 sort_buffer_size = 20M
 read_buffer = 2M
 write_buffer = 2M
 [mysqlhotcopy]
 interactive-timeout

 

 

[sql]  view plain  copy

 

 # Example MySQL config file for medium systems.
 #
 # This is for a system with little memory (32M - 64M) where MySQL plays
 # an important part, or systems up to 128M where MySQL is used together
 with
 # other programs (such as a web server)
 directory is /var/lib/mysql) or
 # ~/.my.cnf to set user-specific options.
 #
 # In this file, you can use all long options that a program supports.
 # If you want to know which options a program supports, run the program
 # with the "--help" option.
 # The following options will be passed to all MySQL clients
 [client]
 #password = your_password
 port = 3306
 socket = /tmp/mysql.sock
 #socket = /var/lib/mysql/mysql.sock
 # Here follows entries for some specific programs
 # The MySQL server
 [mysqld]
 port = 3306
 socket = /tmp/mysql.sock
 #socket = /var/lib/mysql/mysql.sock
 skip-locking
 key_buffer = 128M
 max_allowed_packet = 1M
 table_cache = 256
 sort_buffer_size = 1M
 net_buffer_length = 16K
 myisam_sort_buffer_size = 1M
 max_connections=120
 #addnew config
 wait_timeout =120
 back_log=100
 read_buffer_size = 1M
 thread_cache=32
 skip-innodb
 skip-bdb
 skip-name-resolve
 join_buffer_size=512k
 query_cache_size = 32M
 interactive_timeout=120
 long_query_time=10
 TCP/IP port at all. This can be a security enhancement,
 # if all processes that need to connect to mysqld run on the same host.
 # All interaction with mysqld must be made via Unix sockets or named pipes.
 # Note that using this option without enabling named pipes on Windows
 # (via the "enable-named-pipe" option) will render mysqld useless!
 #
 #skip-networking
 # Replication Master Server (default)
 # binary logging is required for replication
 #log-bin
 # required unique id between 1 and 2^32 - 1
 # defaults to 1 if master-host is not set
 # but will not function as a master if omitted
 server-id = 1
 # Replication Slave (comment out master section to use this)
 #
 # To configure this host as a replication slave, you can choose between
 # two methods :
 #
 # 1) Use the CHANGE MASTER TO command (fully described in our manual) -
 # the syntax is:
 #
 # CHANGE MASTER TO MASTER_HOST=, MASTER_PORT= ,
 # MASTER_USER=, MASTER_PASSWORD= ;
 #
 # where you replace , , by quoted strings and
 # by the master's port number (3306 by default).
 #
 # Example:
 #
 # CHANGE MASTER TO MASTER_HOST='125.564.12.1', MASTER_PORT=3306,
 # MASTER_USER='joe', MASTER_PASSWORD='secret';
 #
 # OR
 #
 # 2) Set the variables below. However, in case you choose this method,
 then
 # start replication for the first time (even unsuccessfully, for example
 # if you mistyped the password in master-password and the slave fails to
 # connect), the slave will create a master.info file, and any later
 # change in this file to the variables' values below will be ignored and
 # overridden by the content of the master.info file, unless you shutdown
 # the slave server, delete master.info and restart the slaver server.
 # For that reason, you may want to leave the lines below untouched
 # (commented) and instead use CHANGE MASTER TO (see above)
 #
 # required unique id between 2 and 2^32 - 1
 # (and different from the master)
 # defaults to 2 if master-host is set
 # but will not function as a slave if omitted
 #server-id = 2
 #
 # The replication master for this slave - required
 #master-host =
 #
 # The username the slave will use for authentication when connecting
 # to the master - required
 #master-user =
 #
 # The password the slave will authenticate with when connecting to
 # the master - required
 #master-password =
 #
 # The port the master is listening on.
 # optional - defaults to 3306
 #master-port =
 #
 # binary logging - not required for slaves, but recommended
 #log-bin
 # Point the following paths to different dedicated disks
 #tmpdir = /tmp/
 #log-update = /path-to-dedicated-directory/hostname
 # Uncomment the following if you are using BDB tables
 #bdb_cache_size = 4M
 #bdb_max_lock = 10000
 # Uncomment the following if you are using InnoDB tables
 #innodb_log_buffer_size = 8M
 #innodb_flush_log_at_trx_commit = 1
 #innodb_lock_wait_timeout = 50
 [mysqldump]
 quick
 max_allowed_packet = 16M
 [mysql]
 no-auto-rehash
 # Remove the next comment character if you are not familiar with SQL
 #safe-updates
 [isamchk]
 key_buffer = 20M
 sort_buffer_size = 20M
 read_buffer = 2M
 write_buffer = 2M
 [myisamchk]
 key_buffer = 20M
 sort_buffer_size = 20M
 read_buffer = 2M
 write_buffer = 2M
 [mysqlhotcopy]
 interactive-timeout