本文實例講述了mysql慢查詢操作。分享給大家供大家參考，具體如下：
mysql有些sql會執(zhí)行很慢，有可能造成服務(wù)器負載飆升
首先查詢 確定影響負載的是mysql ，使用top命令，ps命令等
其次，進入MySQL，使用show full processlist查詢執(zhí)行中的sql語句，看看問題，使用explain 命令 查看狀態(tài)
最后找出sql語句殺死或者優(yōu)化
centos7上面安裝mariadb服務(wù)
yum -y install mariadb-server mariadb-devel
開啟慢查詢
more /etc/my.cnf.d/server.cnf
[mariadb]
slow_query_log=ON
slow_query_log_file=/usr/local/mysql/data/slow.log
long_query_time=1
啟動mariadb服務(wù)
查詢mysql的慢查詢是否開啟，以及多久的時間以上是慢查詢
MariaDB [(none)]> show variables like '%slow_query%';
+---------------------+--------------------------------+
| Variable_name | Value |
+---------------------+--------------------------------+
| slow_query_log | ON |
| slow_query_log_file | /usr/local/mysql/data/slow.log |
+---------------------+--------------------------------+
2 rows in set (0.00 sec)
MariaDB [(none)]> show variables like 'long_query_time';
+-----------------+----------+
| Variable_name | Value |
+-----------------+----------+
| long_query_time | 1.000000 |
+-----------------+----------+
1 row in set (0.00 sec)
#如果沒用開啟慢查詢，可以在命令行開啟
mysql> set global slow_query_log=1;
Query OK, 0 rows affected (0.00 sec)
測試慢查詢，以及查看日志
MariaDB [(none)]> select sleep(2);
+----------+
| sleep(2) |
+----------+
| 0 |
+----------+
1 row in set (2.00 sec)
[root@localhost ~]# more /usr/local/mysql/data/slow.log
/usr/libexec/mysqld, Version: 5.5.60-MariaDB (MariaDB Server). started with:
Tcp port: 0 Unix socket: /var/lib/mysql/mysql.sock
Time Id Command Argument
# Time: 180930 23:51:07
# User@Host: root[root] @ localhost []
# Thread_id: 2 Schema: QC_hit: No
# Query_time: 2.001017 Lock_time: 0.000000 Rows_sent: 1 Rows_examined: 0
SET timestamp=1538322667;
select sleep(2);
確認慢查詢
MariaDB [(none)]> show full processlist; #查看state慢查詢在進行
+----+------+-----------+------+---------+------+------------+-----------------------+----------+
| Id | User | Host | db | Command | Time | State | Info | Progress |
+----+------+-----------+------+---------+------+------------+-----------------------+----------+
| 3 | root | localhost | NULL | Query | 9 | User sleep | select sleep(10) | 0.000 |
| 4 | root | localhost | NULL | Query | 0 | NULL | show full processlist | 0.000 |
+----+------+-----------+------+---------+------+------------+-----------------------+----------+
2 rows in set (0.00 sec)
MariaDB [(none)]> show full processlist; #查看state慢查詢已經(jīng)結(jié)束，但是用戶登陸了
+----+------+-----------+------+---------+------+-------+-----------------------+----------+
| Id | User | Host | db | Command | Time | State | Info | Progress |
+----+------+-----------+------+---------+------+-------+-----------------------+----------+
| 3 | root | localhost | NULL | Sleep | 1 | | NULL | 0.000 |
| 4 | root | localhost | NULL | Query | 0 | NULL | show full processlist | 0.000 |
+----+------+-----------+------+---------+------+-------+-----------------------+----------+
2 rows in set (0.00 sec)
更多關(guān)于MySQL相關(guān)內(nèi)容感興趣的讀者可查看本站專題：《MySQL查詢技巧大全》、《MySQL常用函數(shù)大匯總》、《MySQL日志操作技巧大全》、《MySQL事務(wù)操作技巧匯總》、《MySQL存儲過程技巧大全》及《MySQL數(shù)據(jù)庫鎖相關(guān)技巧匯總》
希望本文所述對大家MySQL數(shù)據(jù)庫計有所幫助。
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