[MySQL 生产环境内存报警]Select之后Free -m的used总是会一直不停的增加直到100%

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生产环境内存使用率常超85%阀值，以往靠重启解决。此次在测试环境分析，查看内存使用情况后，运行无索引消耗资源的SQL，发现内存使用量增长。尝试调小innodb_buffer_pool_size值，执行SQL后内存仍增加，后续还给出了memory使用率判断方法。

现象是：生产环境的内存使用率经常超过85%阀值，nagios不停报警，以往的处理办法就是restart，一切memery使用率回到65%。还得研究找到问题所在，所以在测试环境进行问题测试分析。

1 先查看问题当前的内存使用情况：
[novamysqladminlt@test-by7db2 ~]$ free -m
total used free shared buffers cached
Mem: 32108 24792 7316 0 824 11019
-/+ buffers/cache: 12948 19159
Swap: 32767 42 32725
[novamysqladminlt@test-by7db2 ~]$

2 去运行一个无索引的消耗资源的sql如下
mysql> select * from tb01 where GROUP_ID>100 limit 10000000, 1000;

3 去运行一个无索引的消耗资源的sql如下
mysql> select * from tb01 where GROUP_ID>100 limit 10000000, 1000;

4 然后去检查内存使用情况：

[mysql@test-by7db2 5.5.25a]$ free -m
             total       used       free     shared    buffers     cached
Mem:         32108      25358       6750          0        824      10976
-/+ buffers/cache:      13557      18550
Swap:        32767         44      32723
[mysql@test-by7db2 5.5.25a]$ free -m
             total       used       free     shared    buffers     cached
Mem:         32108      25399       6709          0        824      10976
-/+ buffers/cache:      13598      18510
Swap:        32767         44      32723
[mysql@test-by7db2 5.5.25a]$ free -m
             total       used       free     shared    buffers     cached
Mem:         32108      26807       5301          0        824      10943
-/+ buffers/cache:      15039      17069
Swap:        32767         44      32723
[mysql@test-by7db2 5.5.25a]$ free -m
             total       used       free     shared    buffers     cached
Mem:         32108      26841       5267          0        824      10939
-/+ buffers/cache:      15077      17031
Swap:        32767         44      32723
[mysql@test-by7db2 5.5.25a]$ free -m
             total       used       free     shared    buffers     cached
Mem:         32108      26862       5246          0        824      10931
-/+ buffers/cache:      15106      17002
Swap:        32767         44      32723
[mysql@test-by7db2 5.5.25a]$ free -m
             total       used       free     shared    buffers     cached
Mem:         32108      26894       5213          0        824      10931
-/+ buffers/cache:      15139      16969
Swap:        32767         44      32723
[mysql@test-by7db2 5.5.25a]$ free -m
             total       used       free     shared    buffers     cached
Mem:         32108      26895       5213          0        824      10931
-/+ buffers/cache:      15139      16969
Swap:        32767         44      32723
[mysql@test-by7db2 5.5.25a]$ free -m
             total       used       free     shared    buffers     cached
Mem:         32108      26895       5213          0        824      10931
-/+ buffers/cache:      15139      16969
Swap:        32767         44      32723
[mysql@test-by7db2 5.5.25a]$ 
[mysql@test-by7db2 5.5.25a]$ free -m
             total       used       free     shared    buffers     cached
Mem:         32108      26895       5212          0        824      10932
-/+ buffers/cache:      15139      16969
Swap:        32767         44      32723
[mysql@test-by7db2 5.5.25a]$ 
[mysql@test-by7db2 5.5.25a]$ free -m
             total       used       free     shared    buffers     cached
Mem:         32108      26896       5211          0        824      10932
-/+ buffers/cache:      15140      16968
Swap:        32767         44      32723
[mysql@test-by7db2 5.5.25a]$ 
[mysql@test-by7db2 5.5.25a]$ free -m
             total       used       free     shared    buffers     cached
Mem:         32108      26896       5211          0        824      10932
-/+ buffers/cache:      15139      16968
Swap:        32767         44      32723
[mysql@test-by7db2 5.5.25a]$ free -m
             total       used       free     shared    buffers     cached
Mem:         32108      26897       5211          0        824      10932
-/+ buffers/cache:      15139      16968
Swap:        32767         44      32723
[mysql@test-by7db2 5.5.25a]$ 
[mysql@test-by7db2 5.5.25a]$ 
[mysql@test-by7db2 5.5.25a]$ free -m
             total       used       free     shared    buffers     cached
Mem:         32108      26897       5211          0        824      10933
-/+ buffers/cache:      15139      16968
Swap:        32767         44      32723
[mysql@test-by7db2 5.5.25a]$

OK，查询跑完了，耗时如下：
......
1000 rows in set (1 min 4.15 sec)

4 检查现在运行完SQL的内存使用情况：

[mysql@test-by7db2 5.5.25a]$ free -m
             total       used       free     shared    buffers     cached
Mem:         32108      26913       5195          0        824      10946
-/+ buffers/cache:      15143      16965
Swap:        32767         44      32723
[mysql@test-by7db2 5.5.25a]$ free -m
             total       used       free     shared    buffers     cached
Mem:         32108      26912       5196          0        824      10946
-/+ buffers/cache:      15141      16967
Swap:        32767         44      32723
[mysql@test-by7db2 5.5.25a]$ 
[mysql@test-by7db2 5.5.25a]$ free -m
             total       used       free     shared    buffers     cached
Mem:         32108      26911       5196          0        824      10946
-/+ buffers/cache:      15140      16967
Swap:        32767         44      32723
[mysql@test-by7db2 5.5.25a]$ free -m
             total       used       free     shared    buffers     cached
Mem:         32108      26911       5196          0        824      10946
-/+ buffers/cache:      15140      16968
Swap:        32767         44      32723

不停的在使用着的内存不停的在增长，used值直线上升。最后等查询结束了，会稳定在26911M上面，不再动弹，但是比原来的25358要高很多。

为了验证这个，再继续执行一个慢sql：
mysql> select * from tb01 where GROUP_ID>100 limit 12000000, 1000;

used继续不停的增长,加大。

5，也许是innodb_buffer_pool_size值太大了，尝试把innodb_buffer_pool_size值调小看看：

现在把innodb_buffer_pool_size值从25000M调整到12000M，试试看效果。
innodb_buffer_pool_size = 12000M

[mysql@test-by7db2 5.5.25a]$ service mysql status
SUCCESS! MySQL running (8913)
[mysql@test-by7db2 5.5.25a]$ service mysql restart
Shutting down MySQL........... SUCCESS!
rm: cannot remove `/var/lock/subsys/mysql': Permission denied
Starting MySQL........... SUCCESS!
[mysql@test-by7db2 5.5.25a]$
[mysql@test-by7db2 5.5.25a]$
[mysql@test-by7db2 5.5.25a]$ free -m
total used free shared buffers cached
Mem: 32108 12752 19356 0 840 9681
-/+ buffers/cache: 2230 29878
Swap: 32767 26 32741
[mysql@test-by7db2 5.5.25a]$

去客户端执行SQL：
mysql> select * from identity.tb01 where GROUP_ID>100 limit 12000000, 1000;

再来看used使用情况：

[novamysqladminlt@eanltemydb5-c000utl ~]$ ssh test-by7db2.abn-sjl.ea.com
Last login: Mon Nov 25 02:55:46 2013 from eanltemydb5-c000utl.abn-sjl.ea.com
[novamysqladminlt@test-by7db2 ~]$ free -m
total used free shared buffers cached
Mem: 32108 14197 17911 0 840 9681
-/+ buffers/cache: 3675 28433
Swap: 32767 26 32741
[novamysqladminlt@test-by7db2 ~]$

used值在增加，再来执行新的SQL语句：

mysql> select * from identity.tb01 where GROUP_ID>100 limit 13000000, 1000;

[novamysqladminlt@test-by7db2 ~]$ free -m
total used free shared buffers cached
Mem: 32108 15682 16426 0 840 9681
-/+ buffers/cache: 5160 26948
Swap: 32767 26 32741

看出每执行一条不同的SQL语句，used值都在增加。

看出执行相同的select语句，内存使用率used没有增加。

mysql> select * from identity.tb01 where GROUP_ID>100 limit 14000000, 1000;
[novamysqladminlt@test-by7db2 ~]$ free -m
total used free shared buffers cached
Mem: 32108 15931 16177 0 840 9681
-/+ buffers/cache: 5408 26699
Swap: 32767 26 32741

使用新的sql语句，used使用的内存从15682增加到15931。

从这里可以看出，不管innodb_buffer_pool_size值设置多大多小，used值总是会增加的，看来分析的思路有误，得换个方向。

6 memory使用率判断：

mysql> SHOW GLOBAL STATUS LIKE 'Innodb_buffer_pool_pages_data'; 
+-------------------------------+--------+
| Variable_name                 | Value  |
+-------------------------------+--------+
| Innodb_buffer_pool_pages_data | 1322836|
+-------------------------------+--------+
1 row in set (0.00 sec)


mysql> SHOW GLOBAL STATUS LIKE 'Innodb_buffer_pool_pages_total';
+--------------------------------+---------+
| Variable_name                  | Value   |
+--------------------------------+---------+
| Innodb_buffer_pool_pages_total | 1344000 |
+--------------------------------+---------+
1 row in set (0.00 sec)


mysql> SHOW GLOBAL STATUS LIKE 'Innodb_page_size';
+------------------+-------+
| Variable_name    | Value |
+------------------+-------+
| Innodb_page_size | 16384 |
+------------------+-------+
1 row in set (0.00 sec)	


Innodb_buffer_pool_pages_data' X 'Innodb_page_size' X 1.05 / (1024*1024*1024)	


Innodb_buffer_pool_pages_data' X 'Innodb_page_size' X 1.05 / (1024*1024*1024)

'Innodb_buffer_pool_pages_data' X 100 / 'Innodb_buffer_pool_pages_total'
当结果 > 95% 则增加 innodb_buffer_pool_size，建议使用 ram total 75%
当结果 < 95% 则减少 innodb_buffer_pool_size，
建议 'Innodb_buffer_pool_pages_data' X 'Innodb_page_size' X 1.05 / (1024*1024*1024)

这计算 'Innodb_buffer_pool_pages_data' X 100 / 'Innodb_buffer_pool_pages_total' 值是

mysql> select 1322836*100/1344000;
+---------------------+
| 1322836*100/1344000 |
+---------------------+
|             98.4253 |
+---------------------+
1 row in set (0.00 sec)

[...持续分析中...]