mysql性能问题小解 Converting HEAP to MyIsam create_myisa

安定北京被性能测试困扰了N天，实在没想法去解决了，今天又收到上级的命令说安定北京要解决，无奈！把项目组唯一的DBA辞掉了，现在所以数据库的问题都得自己来处理：（ 不知道上边人怎么想的。而且更不知道怎安定北京么想的是居然会把应用部属在虚拟主机上！唉。。。 不唠叨了 说说处理过程吧： 1.在终端里set profiling=1; 2.输入要调整的SQL语句，比如select * from table1; 3.输入show profiles;看看刚才那条语句的ID 用于后面分析 4.show profile for query 2; 5.show profile block io,cpu for query 2; 6.show profile cpu,block io,memory,swaps,context switches,source for query 5; 7.通过上面的一些查询 大体可以看出这条SQL语句执行的时候哪些地方占用的时间太大了。这次测试看到的是Copying to tmp table on disk和converting HEAP to MyISAM占有的时间太多。网上查了一下发现可以修改一下tmp_table_size和max_heap_table_size两个参数来调整，使得大数据量的查询时不用将结果集拷贝到物理磁盘。这样时间就争取过来了 对了 MYSQL有个好用的命令可以分析一条SQL的结构，可以查到这个查询是否使用到索引等。直接explain select * from table1就行了 +--------------------------------+------------+------------+------------+-------------------+---------------------+--------------+---------------+-------+---------------------------+---------------+-------------+ | Status                         | Duration   | CPU_user   | CPU_system | Context_voluntary | Context_involuntary | Block_ops_in | Block_ops_out | Swaps | Source_function           | Source_file   | Source_line | +--------------------------------+------------+------------+------------+-------------------+---------------------+--------------+---------------+-------+---------------------------+---------------+-------------+ | checking query cache for query | 0.00001100 | 0.00000000 | 0.00000000 |                 0 |                   0 |            0 |             0 |     0 | send_result_to_client     | sql_cache.cc  |        1094 | | Opening tables                 | 0.00023400 | 0.00000000 | 0.00000000 |                 0 |                   0 |            0 |             0 |     0 | open_tables               | sql_base.cc   |        2106 | | System lock                    | 0.00002800 | 0.00000000 | 0.00000000 |                 0 |                   0 |            0 |             0 |     0 | mysql_lock_tables         | lock.cc       |         153 | | Table lock                     | 0.00001300 | 0.00000000 | 0.00000000 |                 0 |                   0 |            0 |             0 |     0 | mysql_lock_tables         | lock.cc       |         162 | | optimizing                     | 0.00022700 | 0.00099900 | 0.00000000 |                 0 |                   0 |            0 |             0 |     0 | optimize                  | sql_select.cc |         617 | | statistics                     | 0.00002900 | 0.00000000 | 0.00000000 |                 0 |                   0 |            0 |             0 |     0 | optimize                  | sql_select.cc |         773 | | preparing                      | 0.00012800 | 0.00000000 | 0.00000000 |                 0 |                   0 |            0 |             0 |     0 | optimize                  | sql_select.cc |         783 | | Creating tmp table             | 0.00003400 | 0.00000000 | 0.00000000 |                 0 |                   0 |            0 |             0 |     0 | optimize                  | sql_select.cc |        1206 | | executing                      | 0.00003100 | 0.00000000 | 0.00000000 |                 0 |                   0 |            0 |             0 |     0 | exec                      | sql_select.cc |        1407 | | Copying to tmp table           | 0.00001100 | 0.00000000 | 0.00000000 |                 0 |                   0 |            0 |             0 |     0 | exec                      | sql_select.cc |        1547 | | converting HEAP to MyISAM      | 3.94055900 | 3.81042100 | 0.12498100 |                 6 |                   7 |            0 |             0 |     0 | create_myisam_from_heap   | sql_select.cc |        9914 | | Copying to tmp table on disk   | 5.10490400 | 5.00623900 | 0.09798500 |                 8 |                  10 |            0 |             0 |     0 | create_myisam_from_heap   | sql_select.cc |        9968 | | Sending data                   | 3.09531800 | 2.96954900 | 0.12698100 |                 4 |                   4 |            0 |             0 |     0 | exec                      | sql_select.cc |        1925 | | converting HEAP to MyISAM      | 1.62242300 | 1.37279100 | 0.25096200 |                38 |                  15 |            0 |             0 |     0 | create_myisam_from_heap   | sql_select.cc |        9914 | | Sending data                   | 5.13815600 | 5.04223300 | 0.09698500 |                13 |                  10 |            0 |             0 |     0 | create_myisam_from_heap   | sql_select.cc |        9968 | | optimizing                     | 2.17403900 | 2.01069500 | 0.16497500 |                 5 |                   3 |            0 |             0 |     0 | optimize                  | sql_select.cc |         617 | mysql官网论坛也有讲过这配置 但没说到第二项配置 http://forums.mysql.com/read.php?22,111012,111012#msg-111012

来源： <http://www.thinksaas.cn/group/topic/124436/>

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http://www.mysqlab.net/knowledge/kb/detail/topic/myisam/id/6149

Discussion

The state "converting HEAP to MyISAM" happens when a query that needs a temporary table is converting from an in-memory temporary table to a disk-based temporary table.

MySQL uses memory-based temporary tables up to the size limit set by the tmp_table_size system variable. If a query needs a temporary table larger than this it will be converted to a disk-based temporary table using the MyISAM storage engine.

GROUP BY queries and ORDER BY queries that can't use an index for the ordering are the most common causes of temporary table creation.

Solution

You could consider raising the per-session value of tmp_table_size if you have sufficient memory. Use the SHOW GLOBAL STATUS statement to see the value of the Created_tmp_tables variable. It will show the total number of temporary tables that have been created:

SHOW GLOBAL STATUS LIKE 'Created_tmp_tables';
 
+--------------------+-------+
| Variable_name      | Value |
+--------------------+-------+
| Created_tmp_tables | 13    |
+--------------------+-------+

The

Created_tmp_disk_tables

variable shows how many of those have been converted to disk temporary tables:

SHOW GLOBAL STATUS LIKE 'Created_tmp_disk_tables';
 
+-------------------------+-------+
| Variable_name           | Value |
+-------------------------+-------+
| Created_tmp_disk_tables | 1     |
+-------------------------+-------+

调2个参数

tmp_table_size和max_heap_table_size ============> converting HEAP to MyISAM

来源： <http://7567567.blog.51cto.com/706378/630036>

来自为知笔记(Wiz)