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MySQL 内存使用情况

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MySQL 内存使用情况

我们的 MySQL 服务器似乎正在使用大量内存。

我尝试寻找慢查询和没有索引的查询，并将峰值 CPU 使用率和 Apache 内存使用率减半，但 MySQL 内存仍然保持在 2.2GB（服务器可用内存的约 51％）。

这是来自 Plesk 的图表。在 SSH 窗口中运行 top 会显示相同的数字。

在此处输入图片描述

有谁知道为什么内存使用情况像这样恒定而不是随着应用程序的使用而出现高峰和低谷？

以下是 MySQL Tuning Primer 脚本的输出：

        -- MYSQL PERFORMANCE TUNING PRIMER --
             - By: Matthew Montgomery -

MySQL Version 5.0.77-log x86_64

Uptime = 1 days 14 hrs 4 min 21 sec
Avg. qps = 22
Total Questions = 3059456
Threads Connected = 13

Warning: Server has not been running for at least 48hrs.
It may not be safe to use these recommendations

To find out more information on how each of these
runtime variables effects performance visit:
http://dev.mysql.com/doc/refman/5.0/en/server-system-variables.html
Visit http://www.mysql.com/products/enterprise/advisors.html
for info about MySQL's Enterprise Monitoring and Advisory Service

SLOW QUERIES
The slow query log is enabled.
Current long_query_time = 1 sec.
You have 6 out of 3059477 that take longer than 1 sec. to complete
Your long_query_time seems to be fine

BINARY UPDATE LOG
The binary update log is NOT enabled.
You will not be able to do point in time recovery
See http://dev.mysql.com/doc/refman/5.0/en/point-in-time-recovery.html

WORKER THREADS
Current thread_cache_size = 0
Current threads_cached = 0
Current threads_per_sec = 2
Historic threads_per_sec = 0
Threads created per/sec are overrunning threads cached
You should raise thread_cache_size

MAX CONNECTIONS
Current max_connections = 100
Current threads_connected = 14
Historic max_used_connections = 20
The number of used connections is 20% of the configured maximum.
Your max_connections variable seems to be fine.

INNODB STATUS
Current InnoDB index space = 6 M
Current InnoDB data space = 18 M
Current InnoDB buffer pool free = 0 %
Current innodb_buffer_pool_size = 8 M
Depending on how much space your innodb indexes take up it may be safe
to increase this value to up to 2 / 3 of total system memory

MEMORY USAGE
Max Memory Ever Allocated : 2.07 G
Configured Max Per-thread Buffers : 274 M
Configured Max Global Buffers : 2.01 G
Configured Max Memory Limit : 2.28 G
Physical Memory : 3.84 G
Max memory limit seem to be within acceptable norms

KEY BUFFER
Current MyISAM index space = 4 M
Current key_buffer_size = 7 M
Key cache miss rate is 1 : 40
Key buffer free ratio = 81 %
Your key_buffer_size seems to be fine

QUERY CACHE
Query cache is supported but not enabled
Perhaps you should set the query_cache_size

SORT OPERATIONS
Current sort_buffer_size = 2 M
Current read_rnd_buffer_size = 256 K
Sort buffer seems to be fine

JOINS
Current join_buffer_size = 132.00 K
You have had 16 queries where a join could not use an index properly
You should enable "log-queries-not-using-indexes"
Then look for non indexed joins in the slow query log.
If you are unable to optimize your queries you may want to increase your
join_buffer_size to accommodate larger joins in one pass.

Note! This script will still suggest raising the join_buffer_size when
ANY joins not using indexes are found.

OPEN FILES LIMIT
Current open_files_limit = 1024 files
The open_files_limit should typically be set to at least 2x-3x
that of table_cache if you have heavy MyISAM usage.
Your open_files_limit value seems to be fine

TABLE CACHE
Current table_cache value = 64 tables
You have a total of 426 tables
You have 64 open tables.
Current table_cache hit rate is 1%
, while 100% of your table cache is in use
You should probably increase your table_cache

TEMP TABLES
Current max_heap_table_size = 16 M
Current tmp_table_size = 32 M
Of 15134 temp tables, 9% were created on disk
Effective in-memory tmp_table_size is limited to max_heap_table_size.
Created disk tmp tables ratio seems fine

TABLE SCANS
Current read_buffer_size = 128 K
Current table scan ratio = 2915 : 1
read_buffer_size seems to be fine

TABLE LOCKING
Current Lock Wait ratio = 1 : 142213
Your table locking seems to be fine

该应用程序是一款 Facebook 游戏，大约有 50-100 个并发用户。

谢谢，罗布

答案1

MySQL 故意使用大量内存——更多内存 = 更少磁盘访问 = 更好的性能。使用率的恒定性可能是由于表缓存、键缓存和查询缓存。如果您希望它使用更少的内存，您可以调整 my.conf 文件中的参数；但请注意，如果您减少内存，它可能会变慢。

看一眼http://hackmysql.com/mysqlreport；您可能能够从中获得一些有用的信息，了解如何在不损失性能的情况下进行调整。

答案2

对于常规优化，请尝试 mysqltuner：https://raw.github.com/major/MySQLTuner-perl/master/mysqltuner.pl

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