分析SQL執行帶來的開銷是優化SQL的重要手段。
在MySQL數據庫中，可以通過配置profiling參數來啟用SQL剖析。該參數可以在全局和session級別來設置。對於全局級別則作用於整個MySQL實例，而session級別緊影響當前session。
該參數開啟后，后續執行的SQL語句都將記錄其資源開銷，諸如IO，上下文切換，CPU，Memory等等。根據這些開銷進一步分析當前SQL瓶頸從而進行優化與調整。 【時間單位為 s】
1.有關profile的解釋 --當前版本 mysql> show variables like 'version'; +---------------+------------+ | Variable_name | Value | +---------------+------------+ | version | 5.5.29-log | +---------------+------------+ --查看profiling系統變量 mysql> show variables like '%profil%'; +------------------------+-------+ | Variable_name | Value | +------------------------+-------+ | profiling | OFF | --開啟SQL語句剖析功能。0或OFF表示關閉(默認模式)。1或ON表示開啟 | profiling_history_size | 15 | --設置保留profiling的數目，缺省為15(即使用show profiles;命令展示的默認是最近執行的15條sql的記錄)，范圍為0至100，為0時將禁用profiling。這個參數在MySQL 5.6.8過期，在后期版本中會被移除。 +------------------------+-------+ 如果將profiling_history_size參數設置為0，同樣具有關閉MySQL的profiling效果。 --獲取profile的幫助 mysql> help profile; Name: 'SHOW PROFILE' Description: Syntax: SHOW PROFILE [type [, type] ... ] [FOR QUERY n] --如果不指定，只是顯示最近執行的語句；如果指定會顯示語句n，n對應query_id的值 [LIMIT row_count [OFFSET offset]] type: ALL --顯示所有的開銷信息 | BLOCK IO --顯示塊IO相關開銷 | CONTEXT SWITCHES --上下文切換相關開銷 | CPU --顯示CPU相關開銷信息 | IPC --顯示發送和接收相關開銷信息 | MEMORY --顯示內存相關開銷信息 | PAGE FAULTS --顯示頁面錯誤相關開銷信息 | SOURCE --顯示和Source_function，Source_file，Source_line相關的開銷信息 | SWAPS --顯示交換次數相關開銷的信息 Profiling由會話級別參數profiling控制。缺省是顯示狀態和持續時間。 上面描述從5.6.7開始該命令將會被移除，用Performance Schema instead代替 2、開啟porfiling --啟用session級別的profiling mysql> set profiling=1; Query OK, 0 rows affected, 1 warning (0.00 sec) --驗證修改后的結果 mysql> show variables like '%profil%'; +------------------------+-------+ | Variable_name | Value | +------------------------+-------+ | profiling | ON | | profiling_history_size | 15 | +------------------------+-------+ --執行SQL查詢 mysql> show databases; mysql> show tables; mysql> select count(*) from emp --查看當前session所有已產生的profile【注意，要顯示Query_ID 和 Query列，需要使用的命令是 show profiles;】 mysql> show profiles; +----------+------------+-------------------------------------------------------+ | Query_ID | Duration | Query | --------------------------------------------------------------------------------+ | 1 | 0.00037700 | show variables like '%profil%' | | 2 | 0.00029500 | show databases | | 3 | 0.00030800 | show tables | | 4 | 0.00135700 | select count(*) from emp +----------+------------+-------------------------------------------------------+
3、獲取SQL語句的開銷信息 --可以直接使用show profile來查看上一條SQL語句的開銷信息 --注，show profile之類的語句不會被profiling，即自身不會產生Profiling mysql> show profile; +--------------------+----------+ | Status | Duration | +--------------------+----------+ | starting | 0.000997 | | Opening tables | 0.000015 | | System lock | 0.000003 | | Table lock | 0.000515 | | optimizing | 0.000093 | | statistics | 0.151343 | | preparing | 0.000082 | | executing | 0.000027 | | Sending data | 0.081436 | | init | 0.000024 | | optimizing | 0.000006 | | statistics | 0.000006 | | preparing | 0.000007 | | executing | 0.000005 | | Sending data | 0.000046 | | end | 0.000004 | | query end | 0.000003 | | freeing items | 0.000076 | | removing tmp table | 0.000006 | | closing tables | 0.000004 | | logging slow query | 0.000002 | | cleaning up | 0.000004 | +--------------------+----------+ --顯示所有性能信息【這里的9 就是使用上面的 show profiles;命令獲取到的 自己想要查看的哪個 sql語句的 Query_ID】 mysql> show profile all for query 9; +--------------------+----------+----------+------------+-------------------+---------------------+--------------+---------------+---------------+-------------------+-------------------+-------------------+-------+------------------+---------------+-------------+ | Status | Duration | CPU_user | CPU_system | Context_voluntary | Context_involuntary | Block_ops_in | Block_ops_out | Messages_sent | Messages_received | Page_faults_major | Page_faults_minor | Swaps | Source_function | Source_file | Source_line | +--------------------+----------+----------+------------+-------------------+---------------------+--------------+---------------+---------------+-------------------+-------------------+-------------------+-------+------------------+---------------+-------------+ | starting | 0.000997 | 0.000000 | 0.000000 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | NULL | NULL | NULL | | Opening tables | 0.000015 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_base.cc | 4622 | | System lock | 0.000003 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | lock.cc | 260 | | Table lock | 0.000515 | 0.001000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | lock.cc | 271 | | optimizing | 0.000093 | 0.000000 | 0.000000 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 835 | | statistics | 0.151343 | 0.124981 | 0.023996 | 1 | 155 | 0 | 0 | 0 | 0 | 0 | 39 | 0 | unknown function | sql_select.cc | 1026 | | preparing | 0.000082 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 1048 | | executing | 0.000027 | 0.000000 | 0.000000 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 1789 | | Sending data | 0.081436 | 0.072989 | 0.006999 | 0 | 82 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 2347 | | init | 0.000024 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 2537 | | optimizing | 0.000006 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 835 | | statistics | 0.000006 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 1026 | | preparing | 0.000007 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 1048 | | executing | 0.000005 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 1789 | | Sending data | 0.000046 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 2347 | | end | 0.000004 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 2583 | | query end | 0.000003 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_parse.cc | 5123 | | freeing items | 0.000076 | 0.001000 | 0.000000 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_parse.cc | 6147 | | removing tmp table | 0.000006 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 10929 | | closing tables | 0.000004 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_select.cc | 10954 | | logging slow query | 0.000002 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_parse.cc | 1735 | | cleaning up | 0.000004 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | unknown function | sql_parse.cc | 1703 | +--------------------+----------+----------+------------+-------------------+---------------------+--------------+---------------+---------------+-------------------+-------------------+-------------------+-------+------------------+---------------+-------------+ --獲取指定查詢的開銷 mysql> show profile for query 9; +--------------------+----------+ | Status | Duration | +--------------------+----------+ | starting | 0.000997 | | Opening tables | 0.000015 | | System lock | 0.000003 | | Table lock | 0.000515 | | optimizing | 0.000093 | | statistics | 0.151343 | | preparing | 0.000082 | | executing | 0.000027 | | Sending data | 0.081436 | | init | 0.000024 | | optimizing | 0.000006 | | statistics | 0.000006 | | preparing | 0.000007 | | executing | 0.000005 | | Sending data | 0.000046 | | end | 0.000004 | | query end | 0.000003 | | freeing items | 0.000076 | | removing tmp table | 0.000006 | | closing tables | 0.000004 | | logging slow query | 0.000002 | | cleaning up | 0.000004 | +--------------------+----------+ mysql> show profile for query 9 limit 3; +----------------+----------+ | Status | Duration | +----------------+----------+ | starting | 0.000997 | | Opening tables | 0.000015 | | System lock | 0.000003 | +----------------+----------+ mysql> show profile for query 9 limit 3 offset 5; +------------+----------+ | Status | Duration | +------------+----------+ | statistics | 0.151343 | | preparing | 0.000082 | | executing | 0.000027 | +------------+----------+ --查看特定部分的開銷，如下為CPU部分的開銷 mysql> show profile cpu for query 9; +--------------------+----------+----------+------------+ | Status | Duration | CPU_user | CPU_system | +--------------------+----------+----------+------------+ | starting | 0.000997 | 0.000000 | 0.000000 | | Opening tables | 0.000015 | 0.000000 | 0.000000 | | System lock | 0.000003 | 0.000000 | 0.000000 | | Table lock | 0.000515 | 0.001000 | 0.000000 | | optimizing | 0.000093 | 0.000000 | 0.000000 | | statistics | 0.151343 | 0.124981 | 0.023996 | | preparing | 0.000082 | 0.000000 | 0.000000 | | executing | 0.000027 | 0.000000 | 0.000000 | | Sending data | 0.081436 | 0.072989 | 0.006999 | | init | 0.000024 | 0.000000 | 0.000000 | | optimizing | 0.000006 | 0.000000 | 0.000000 | | statistics | 0.000006 | 0.000000 | 0.000000 | | preparing | 0.000007 | 0.000000 | 0.000000 | | executing | 0.000005 | 0.000000 | 0.000000 | | Sending data | 0.000046 | 0.000000 | 0.000000 | | end | 0.000004 | 0.000000 | 0.000000 | | query end | 0.000003 | 0.000000 | 0.000000 | | freeing items | 0.000076 | 0.001000 | 0.000000 | | removing tmp table | 0.000006 | 0.000000 | 0.000000 | | closing tables | 0.000004 | 0.000000 | 0.000000 | | logging slow query | 0.000002 | 0.000000 | 0.000000 | | cleaning up | 0.000004 | 0.000000 | 0.000000 | +--------------------+----------+----------+------------+ --如下為MEMORY部分的開銷 mysql> show profile memory for query 9 ; +--------------------+----------+ | Status | Duration | +--------------------+----------+ | starting | 0.000997 | | Opening tables | 0.000015 | | System lock | 0.000003 | | Table lock | 0.000515 | | optimizing | 0.000093 | | statistics | 0.151343 | | preparing | 0.000082 | | executing | 0.000027 | | Sending data | 0.081436 | | init | 0.000024 | | optimizing | 0.000006 | | statistics | 0.000006 | | preparing | 0.000007 | | executing | 0.000005 | | Sending data | 0.000046 | | end | 0.000004 | | query end | 0.000003 | | freeing items | 0.000076 | | removing tmp table | 0.000006 | | closing tables | 0.000004 | | logging slow query | 0.000002 | | cleaning up | 0.000004 | +--------------------+----------+ --同時查看不同資源開銷 mysql> show profile block io,cpu for query 9; +--------------------+----------+----------+------------+--------------+---------------+ | Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out | +--------------------+----------+----------+------------+--------------+---------------+ | starting | 0.000997 | 0.000000 | 0.000000 | 0 | 0 | | Opening tables | 0.000015 | 0.000000 | 0.000000 | 0 | 0 | | System lock | 0.000003 | 0.000000 | 0.000000 | 0 | 0 | | Table lock | 0.000515 | 0.001000 | 0.000000 | 0 | 0 | | optimizing | 0.000093 | 0.000000 | 0.000000 | 0 | 0 | | statistics | 0.151343 | 0.124981 | 0.023996 | 0 | 0 | | preparing | 0.000082 | 0.000000 | 0.000000 | 0 | 0 | | executing | 0.000027 | 0.000000 | 0.000000 | 0 | 0 | | Sending data | 0.081436 | 0.072989 | 0.006999 | 0 | 0 | | init | 0.000024 | 0.000000 | 0.000000 | 0 | 0 | | optimizing | 0.000006 | 0.000000 | 0.000000 | 0 | 0 | | statistics | 0.000006 | 0.000000 | 0.000000 | 0 | 0 | | preparing | 0.000007 | 0.000000 | 0.000000 | 0 | 0 | | executing | 0.000005 | 0.000000 | 0.000000 | 0 | 0 | | Sending data | 0.000046 | 0.000000 | 0.000000 | 0 | 0 | | end | 0.000004 | 0.000000 | 0.000000 | 0 | 0 | | query end | 0.000003 | 0.000000 | 0.000000 | 0 | 0 | | freeing items | 0.000076 | 0.001000 | 0.000000 | 0 | 0 | | removing tmp table | 0.000006 | 0.000000 | 0.000000 | 0 | 0 | | closing tables | 0.000004 | 0.000000 | 0.000000 | 0 | 0 | | logging slow query | 0.000002 | 0.000000 | 0.000000 | 0 | 0 | | cleaning up | 0.000004 | 0.000000 | 0.000000 | 0 | 0 | +--------------------+----------+----------+------------+--------------+---------------+ --顯示swap的次數。 mysql> show profile swaps for query 9; +--------------------+----------+-------+ | Status | Duration | Swaps | +--------------------+----------+-------+ | starting | 0.000997 | 0 | | Opening tables | 0.000015 | 0 | | System lock | 0.000003 | 0 | | Table lock | 0.000515 | 0 | | optimizing | 0.000093 | 0 | | statistics | 0.151343 | 0 | | preparing | 0.000082 | 0 | | executing | 0.000027 | 0 | | Sending data | 0.081436 | 0 | | init | 0.000024 | 0 | | optimizing | 0.000006 | 0 | | statistics | 0.000006 | 0 | | preparing | 0.000007 | 0 | | executing | 0.000005 | 0 | | Sending data | 0.000046 | 0 | | end | 0.000004 | 0 | | query end | 0.000003 | 0 | | freeing items | 0.000076 | 0 | | removing tmp table | 0.000006 | 0 | | closing tables | 0.000004 | 0 | | logging slow query | 0.000002 | 0 | | cleaning up | 0.000004 | 0 | +--------------------+----------+-------+ --下面的SQL語句用於查詢query_id為9的SQL開銷，且按最大耗用時間倒序排列 mysql> set @query_id=9; mysql> SELECT STATE, -> SUM(DURATION) AS Total_R, -> ROUND(100 * SUM(DURATION) / -> (SELECT SUM(DURATION) -> FROM INFORMATION_SCHEMA.PROFILING -> WHERE QUERY_ID = @query_id), -> 2) AS Pct_R, -> COUNT(*) AS Calls, -> SUM(DURATION) / COUNT(*) AS "R/Call" -> FROM INFORMATION_SCHEMA.PROFILING -> WHERE QUERY_ID = @query_id -> GROUP BY STATE -> ORDER BY Total_R DESC; +--------------------+----------+-------+-------+--------------+ | STATE | Total_R | Pct_R | Calls | R/Call | +--------------------+----------+-------+-------+--------------+ | statistics | 0.151349 | 64.49 | 2 | 0.0756745000 |--最大耗用時間部分為statistics | Sending data | 0.081482 | 34.72 | 2 | 0.0407410000 | | starting | 0.000997 | 0.42 | 1 | 0.0009970000 | | Table lock | 0.000515 | 0.22 | 1 | 0.0005150000 | | optimizing | 0.000099 | 0.04 | 2 | 0.0000495000 | | preparing | 0.000089 | 0.04 | 2 | 0.0000445000 | | freeing items | 0.000076 | 0.03 | 1 | 0.0000760000 | | executing | 0.000032 | 0.01 | 2 | 0.0000160000 | | init | 0.000024 | 0.01 | 1 | 0.0000240000 | | Opening tables | 0.000015 | 0.01 | 1 | 0.0000150000 | | removing tmp table | 0.000006 | 0.00 | 1 | 0.0000060000 | | cleaning up | 0.000004 | 0.00 | 1 | 0.0000040000 | | end | 0.000004 | 0.00 | 1 | 0.0000040000 | | closing tables | 0.000004 | 0.00 | 1 | 0.0000040000 | | query end | 0.000003 | 0.00 | 1 | 0.0000030000 | | System lock | 0.000003 | 0.00 | 1 | 0.0000030000 | | logging slow query | 0.000002 | 0.00 | 1 | 0.0000020000 | +--------------------+----------+-------+-------+--------------+ --開啟profiling后，我們可以通過show profile等方式查看，其實質是這些開銷信息被記錄到information_schema.profiling表 --如下面的查詢，部分信息省略 mysql> select * from profiling limit 3,3\G; *************************** 1. row *************************** QUERY_ID: 2 SEQ: 4 STATE: Table lock DURATION: 0.000007 CPU_USER: 0.000000 CPU_SYSTEM: 0.000000 CONTEXT_VOLUNTARY: 0 CONTEXT_INVOLUNTARY: 0 BLOCK_OPS_IN: 0 BLOCK_OPS_OUT: 0 MESSAGES_SENT: 0 MESSAGES_RECEIVED: 0 PAGE_FAULTS_MAJOR: 0 PAGE_FAULTS_MINOR: 0 SWAPS: 0 SOURCE_FUNCTION: unknown function SOURCE_FILE: lock.cc SOURCE_LINE: 271 *************************** 2. row *************************** QUERY_ID: 2 SEQ: 5 STATE: init DURATION: 0.000010 CPU_USER: 0.000000 CPU_SYSTEM: 0.000000 CONTEXT_VOLUNTARY: 0 CONTEXT_INVOLUNTARY: 0 BLOCK_OPS_IN: 0 BLOCK_OPS_OUT: 0 MESSAGES_SENT: 0 MESSAGES_RECEIVED: 0 PAGE_FAULTS_MAJOR: 0 PAGE_FAULTS_MINOR: 0 SWAPS: 0 SOURCE_FUNCTION: unknown function SOURCE_FILE: sql_select.cc SOURCE_LINE: 2537 *************************** 3. row *************************** QUERY_ID: 2 SEQ: 6 STATE: optimizing DURATION: 0.000003 CPU_USER: 0.000000 CPU_SYSTEM: 0.000000 CONTEXT_VOLUNTARY: 0 CONTEXT_INVOLUNTARY: 0 BLOCK_OPS_IN: 0 BLOCK_OPS_OUT: 0 MESSAGES_SENT: 0 MESSAGES_RECEIVED: 0 PAGE_FAULTS_MAJOR: 0 PAGE_FAULTS_MINOR: 0 SWAPS: 0 SOURCE_FUNCTION: unknown function SOURCE_FILE: sql_select.cc SOURCE_LINE: 835 3 rows in set (0.00 sec) ERROR: No query specified mysql> --停止profile,可以設置profiling參數，或者在session退出之后,profiling會被自動關閉 mysql> set profiling=off; Query OK, 0 rows affected, 1 warning (0.00 sec)