Abd*_*naf 6 mysql performance transaction mysql-5.1 query-performance
我有一个busy MySQL Server查询
SELECT sys_sess_state, index_state, timeout_lvl, last_queued_dt,
last_polled_wait_dt, create_id, create_dt, modify_id,
modify_dt
FROM PQR_AM_SYSTEM_SESSION
WHERE (pqr_sess_id=592885621) FOR UPDATE
哪里pqr_sess_id是Primary Key在表中。
当我独立执行查询时，它正在完成，0.00 secs,但我多次观察到挂起的查询是带有状态统计信息的进程列表。
可能是什么问题，我在慢日志中发现此查询的计数超过 10K 次。
mysql> show full processlist;
+------+-----------------+---------------------+-----------+---------+------+-----------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Id | User | Host | db | Command | Time | State | Info |
+------+-----------------+---------------------+-----------+---------+------+-----------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| 2899 | root | 192.168.9.217:49340 | abdulrony | Query | 58 | statistics | SELECT sys_sess_state, index_state, timeout_lvl, last_queued_dt, last_polled_wait_dt, create_id, create_dt, modify_id, modify_dt FROM PQR_AM_SYSTEM_SESSION WHERE (pqr_sess_id=592885621) FOR UPDATE |
| 2977 | root | 192.168.9.217:35082 | abdulrony | Query | 30 | statistics | SELECT sys_sess_state, index_state, timeout_lvl, last_queued_dt, last_polled_wait_dt, create_id, create_dt, modify_id, modify_dt FROM PQR_AM_SYSTEM_SESSION WHERE (pqr_sess_id=593059341) FOR UPDATE |
| 3010 | root | 192.168.9.217:44607 | abdulrony | Query | 3 | statistics | SELECT sys_sess_state, index_state, timeout_lvl, last_queued_dt, last_polled_wait_dt, create_id, create_dt, modify_id, modify_dt FROM PQR_AM_SYSTEM_SESSION WHERE (pqr_sess_id=595647701) FOR UPDATE |
| 3011 | root | 192.168.9.217:44287 | abdulrony | Query | 33 | statistics | SELECT sys_sess_state, index_state, timeout_lvl, last_queued_dt, last_polled_wait_dt, create_id, create_dt, modify_id, modify_dt FROM PQR_AM_SYSTEM_SESSION WHERE (pqr_sess_id=593503321) FOR UPDATE |
| 3014 | root | 192.168.9.217:49280 | abdulrony | Query | 3 | statistics | SELECT sys_sess_state, index_state, timeout_lvl, last_queued_dt, last_polled_wait_dt, create_id, create_dt, modify_id, modify_dt FROM PQR_AM_SYSTEM_SESSION WHERE (pqr_sess_id=595641601) FOR UPDATE |
| 3016 | root | 192.168.9.217:60243 | abdulrony | Query | 51 | statistics | SELECT sys_sess_state, index_state, timeout_lvl, last_queued_dt, last_polled_wait_dt, create_id, create_dt, modify_id, modify_dt FROM PQR_AM_SYSTEM_SESSION WHERE (pqr_sess_id=592248641) FOR UPDATE |
| 3033 | root | 192.168.9.217:49695 | abdulrony | Query | 22 | statistics | SELECT sys_sess_state, index_state, timeout_lvl, last_queued_dt, last_polled_wait_dt, create_id, create_dt, modify_id, modify_dt FROM PQR_AM_SYSTEM_SESSION WHERE (pqr_sess_id=594780861) FOR UPDATE |
| 3034 | root | 192.168.9.217:44473 | abdulrony | Query | 27 | statistics | SELECT sys_sess_state, index_state, timeout_lvl, last_queued_dt, last_polled_wait_dt, create_id, create_dt, modify_id, modify_dt FROM PQR_AM_SYSTEM_SESSION WHERE (pqr_sess_id=594503601) FOR UPDATE |
| 3038 | root | 192.168.9.217:55093 | abdulrony | Query | 1 | statistics | SELECT sys_sess_state, index_state, timeout_lvl, last_queued_dt, last_polled_wait_dt, create_id, create_dt, modify_id, modify_dt FROM PQR_AM_SYSTEM_SESSION WHERE (pqr_sess_id=595625241) FOR UPDATE |
+------+-----------------+---------------------+-----------+---------+------+-----------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
22 rows in set (0.00 sec)
我知道我可以optimizer_search_depth通过将其设置为某个低值来进行调整默认值如下，但我有一个涉及查询的表，所以我认为不会有帮助。
SHOW variables like 'optimizer_search_depth';
+------------------------+-------+
| Variable_name | Value |
+------------------------+-------+
| optimizer_search_depth | 62 |
+------------------------+-------+
1 row in set (0.00 sec)
如果查询时间较长，则statistics表明服务器可能受磁盘限制执行其他工作。
如何减少磁盘绑定：
1）增加innodb_buffer_pool_size的大小
如果您正在使用Innodb表，那么当表数据缓存在 InnoDB 缓冲池中时，它可以通过查询一遍又一遍地处理，而无需任何磁盘 I/O。使用 innodb_buffer_pool_size 选项指定缓冲池的大小。此内存区域非常重要，以至于繁忙的数据库通常指定的大小约为物理内存量的 80%。
2) 在某些版本的 GNU/Linux 和 Unix 中，使用 Unix fsync() 调用（InnoDB 默认使用）和类似方法将文件刷新到磁盘的速度非常慢。如果数据库写入性能是一个问题，请在将 innodb_flush_method 参数设置为 O_DSYNC 的情况下进行基准测试。
3) 增加innodb_log_buffer_size的大小- 设置分配给存储 InnoDB 预写日志条目的缓冲区的内存量。对于大型事务，可以将日志加载到日志缓冲区中，而不是将日志写入磁盘上的日志文件，直到在每次事务提交时刷新日志缓冲区。如果您在运行时在 show innodb status 输出中看到大型日志 I/O，您可能需要为 innodb_log_buffer_size 参数设置更大的值以节省磁盘 I/O。
4）增加用于缓存表和查询内存-检查它们的缓存命中率检查并增加这些MySQL的变量：
query_cache_size，query_cache_limit，query_cache_min_res_unit，tmp_table_size，join_buffer_size，sort_buffer_size等。
5) 确保将正确的索引应用于服务器上的所有表并使用正确的数据类型。
您可以参考这些链接来解决磁盘绑定问题：http : //dev.mysql.com/doc/refman/5.5/en/disk-issues.html https://blogs.oracle.com/luojiach/entry/mysql_innodb_performance_tuning_for