MySQL查詢?nèi)罩窘榻B

MySQL的查詢?nèi)罩居涗浟怂蠱ySQL數(shù)據(jù)庫請(qǐng)求的信息。無論這些請(qǐng)求是否得到了正確的執(zhí)行。默認(rèn)文件名為hostname.log。默認(rèn)情況下MySQL查詢?nèi)罩臼顷P(guān)閉的。生產(chǎn)環(huán)境，如果開啟MySQL查詢?nèi)罩?#xff0c;對(duì)性能還是有蠻大的影響的。另外很多時(shí)候，MySQL慢查詢?nèi)罩净究梢远ㄎ荒切┏霈F(xiàn)性能問題的SQL，所以MySQL查詢?nèi)罩緫?yīng)用的場(chǎng)景其實(shí)不多，有點(diǎn)雞肋的感覺，它跟SQL Server中的profiler有點(diǎn)類似，但是這個(gè)不能跟蹤某個(gè)會(huì)話、用戶、客戶端。它只能對(duì)整個(gè)數(shù)據(jù)庫進(jìn)行跟蹤。MySQL查詢?nèi)罩颈旧肀容^簡(jiǎn)單，網(wǎng)上介紹的不多，官方資料也就那么短短一篇。

MySQL查詢?nèi)罩九渲?/p>

MySQL中的參數(shù)general_log用來控制開啟、關(guān)閉MySQL查詢?nèi)罩?參數(shù)general_log_file用來控制查詢?nèi)罩镜奈恢谩Ｋ匀绻阋袛郙ySQL數(shù)據(jù)庫是否開啟了查詢?nèi)罩?#xff0c;可以使用下面命令。general_log為ON表示開啟查詢?nèi)罩?#xff0c;OFF表示關(guān)閉查詢?nèi)罩尽?/p>

mysql> show variables like?'%general_log%';

+------------------+------------------------------+

| Variable_name??? | Value??????????????????????? |

+------------------+------------------------------+

| general_log????? | OFF????????????????????????? |

| general_log_file | /var/lib/mysql/DB-Server.log |

+------------------+------------------------------+

2 rows?in?set (0.00 sec)

mysql>

另外，MySQL的查詢?nèi)罩局С謱懭胛募驅(qū)懭霐?shù)據(jù)表兩種形式，這個(gè)由參數(shù)log_output控制，如下所示：

mysql> show variables like?'log_output';

+---------------+-------+

| Variable_name | Value |

+---------------+-------+

| log_output??? | FILE? |

+---------------+-------+

1 row?in?set (0.00 sec)

mysql>

這三個(gè)參數(shù)general_log、 general_log_file、 log_output都是動(dòng)態(tài)參數(shù)，可以隨時(shí)動(dòng)態(tài)修改。

1、開啟MySQL查詢?nèi)罩?/p>

mysql> set?global general_log = on;

Query OK, 0 rows affected (0.11 sec)

mysql> show variables like?'general_log';

+---------------+-------+

| Variable_name | Value |

+---------------+-------+

| general_log?? | ON??? |

+---------------+-------+

1 row?in?set (0.02 sec)

mysql>

2：關(guān)閉MySQL查詢?nèi)罩?/p>

mysql> show variables like?'general_log';

+---------------+-------+

| Variable_name | Value |

+---------------+-------+

| general_log?? | ON??? |

+---------------+-------+

1 row?in?set (0.01 sec)

mysql> set?global general_log=off;

Query OK, 0 rows affected (0.01 sec)

mysql> show variables like?'general_log';

+---------------+-------+

| Variable_name | Value |

+---------------+-------+

| general_log?? | OFF?? |

+---------------+-------+

1 row?in?set (0.00 sec)

mysql>

3：設(shè)置日志輸出方式為表(如果設(shè)置log_output=table的話，則日志結(jié)果會(huì)記錄到名為gengera_log的表中，這表的默認(rèn)引擎是CSV)：

mysql> show variables like?'log_output';

+---------------+-------+

| Variable_name | Value |

+---------------+-------+

| log_output??? | FILE? |

+---------------+-------+

1 row?in?set (0.00 sec)

mysql> set?global log_output='table';

Query OK, 0 rows affected (0.00 sec)

mysql> show variables like?'log_output';

+---------------+-------+

| Variable_name | Value |

+---------------+-------+

| log_output??? | TABLE |

+---------------+-------+

1 row?in?set (0.01 sec)

mysql>

查看查詢?nèi)罩拘畔ⅰ?/p>

mysql> select * from mysql.general_log;

+---------------------+---------------------------+-----------+-----------+--------------+----------------------------------+

| event_time????????? | user_host???????????????? | thread_id | server_id | command_type | argument???????????????????????? |

+---------------------+---------------------------+-----------+-----------+--------------+----------------------------------+

| 2017-07-06 12:32:05 | root[root] @ localhost [] |???????? 1 |???????? 1 | Query??????? | show variables like?'general%'?? |

| 2017-07-06 12:32:28 | root[root] @ localhost [] |???????? 1 |???????? 1 | Query??????? | show variables like?'log_output' |

| 2017-07-06 12:32:41 | root[root] @ localhost [] |???????? 1 |???????? 1 | Query??????? | select * from MyDB.test????????? |

| 2017-07-06 12:34:36 | [root] @ localhost []???? |???????? 3 |???????? 1 | Connect????? | root@localhost on??????????????? |

| 2017-07-06 12:34:36 | root[root] @ localhost [] |???????? 3 |???????? 1 | Query??????? | KILL QUERY 1???????????????????? |

| 2017-07-06 12:34:36 | root[root] @ localhost [] |???????? 3 |???????? 1 | Quit???????? |????????????????????????????????? |

| 2017-07-06 12:34:51 | root[root] @ localhost [] |???????? 1 |???????? 1 | Query??????? | select * from mysql.general_log? |

+---------------------+---------------------------+-----------+-----------+--------------+----------------------------------+

7 rows?in?set (0.02 sec)

mysql>

4： 查詢?nèi)罩練w檔

mysql> system mv /var/lib/mysql/DB-Server.log??/var/lib/mysql/DB-Server.log.20170706

mysql> system mysqladmin flush-logs -p

Enter password:

或者你在shell中執(zhí)行下面命令

[root@DB-Server mysql]# mv /var/lib/mysql/DB-Server.log??/var/lib/mysql/DB-Server.log.20170706

[root@DB-Server mysql]# mysqladmin flush-logs -p

Enter password:

5： 修改查詢?nèi)罩久Q或位置

mysql> show variables like?'general_log%';

+------------------+------------------------------+

| Variable_name??? | Value??????????????????????? |

+------------------+------------------------------+

| general_log????? | ON?????????????????????????? |

| general_log_file | /var/lib/mysql/DB-Server.log |

+------------------+------------------------------+

2 rows?in?set (0.00 sec)

mysql> set?global general_log='OFF';

Query OK, 0 rows affected (0.00 sec)

mysql> set?global general_log_file='/u02/mysql_log.log';

Query OK, 0 rows affected (0.00 sec)

mysql> set?global general_log='ON';

Query OK, 0 rows affected (0.02 sec)

如果你遇到下面類似問題，這個(gè)是因?yàn)闄?quán)限問題導(dǎo)致。

mysql> set global general_log_file='/u02/mysql_log.log';

ERROR 1231 (42000): Variable 'general_log_file' can't be set to the value of '/u02/mysql_log.log'

將對(duì)應(yīng)目錄的owner修改為mysql即可解決問題。如下所示：

[root@DB-Server u02]# chown -R mysql:mysql??/u02

另外，MySQL的查詢?nèi)罩居涗浟怂蠱ySQL數(shù)據(jù)庫請(qǐng)求的信息。無論這些請(qǐng)求是否得到了正確的執(zhí)行。這個(gè)就是即使我查詢一個(gè)不存在的表的SQL，查詢?nèi)罩疽廊粫?huì)記錄。如下測(cè)試所示：

mysql> select * from MyDB.test1;

ERROR 1146 (42S02): Table?'MyDB.test1' doesn't exist

mysql> select * from MyDB.test2;

+-------+------+

| id??? | sex? |

+-------+------+

| 10001 |????? |

| 10002 |????? |

| 10003 |???? |

+-------+------+

3 rows in set (0.07 sec)

mysql> select * from MyDB.kkk;

ERROR 1146 (42S02): Table 'MyDB.kkk' doesn't exist

mysql>

MySQL查詢?nèi)罩镜膽?yīng)用場(chǎng)景

存在即是合理，既然MySQL提供了查詢?nèi)罩?#xff0c;那么肯定有其應(yīng)用的地方。比如，我就遇到這樣一個(gè)例子，前陣子碰到別人問mysqlslap壓力測(cè)試工具中參數(shù)的問題，問題如下：

-c, --concurrency=nameNumber of clients to simulate for query to run.

--number-of-queries=#Limiteachclienttothisnumberofqueries(thisisnotexact).

比如我指定：--concurrency=50--number-of-queries=100， 那么這次測(cè)試總的sql執(zhí)行次數(shù)是=100還是50*100=5000 ？

我們不知道--number-of-queries這個(gè)參數(shù)代表所有客戶端的執(zhí)行次數(shù)還是每一個(gè)客戶端的執(zhí)行次數(shù)，這些英文如果看得不是太明白，那么我們就動(dòng)手測(cè)試一下，這個(gè)時(shí)候MySQL查詢?nèi)罩揪湍馨l(fā)揮其用武之地了。

[root@DB-Server u02]# mysqlslap -u root -p --concurrency=50 --create-schema='MyDB'? --query='select * from MyDB.test2'? --number-of-queries=100;

Enter password:

Benchmark

Average number of seconds to run all queries: 0.023 seconds

Minimum number of seconds to run all queries: 0.023 seconds

Maximum number of seconds to run all queries: 0.023 seconds

Number of clients running queries: 50

Average number of queries per client: 2

如下所示，我們可以查到這個(gè)SQL總共執(zhí)行了100次，也就是說number-of-queries代表總共要運(yùn)行多少次查詢。每個(gè)客戶運(yùn)行的查詢數(shù)量可以用查詢總數(shù)/并發(fā)數(shù)來計(jì)算。--concurrency表示并發(fā)量，也就是模擬多少個(gè)客戶端同時(shí)執(zhí)行select。如果你指定--number-of-queries=100，--concurrency=50測(cè)試總的SQL執(zhí)行應(yīng)該是100

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