show profile是由Jeremy Cole捐獻給MySQL社區版本的。默認的是關閉的，但是會話級別可以開啟這個功能。開啟它可以讓MySQL收集在執行語句的時候所使用的資源。為了統計報表,把profiling設為1
mysql> SET profiling = 1;
之後在運行一個查詢
mysql> SELECT COUNT(DISTINCT actor.first_name) AS cnt_name, COUNT(*) AS cnt -> FROM sakila.film_actor -> INNER JOIN sakila.actor USING(actor_id) -> GROUP BY sakila.film_actor.film_id -> ORDER BY cnt_name DESC; ... 997 rows in set (0.03 sec)
這個執行語句的剖析信息存儲在這個會話中。使用SHOW PROFILES進行查看。
mysql> SHOW PROFILES\G
*************************** 1. row *************************** Query_ID: 1 Duration: 0.02596900 Query: SELECT COUNT(DISTINCT actor.first_name) AS cnt_name,...
你可以使用SHOW PROFILE語句來獲取已經存儲的剖析數據。如果不加參數，會顯示狀態以及它們持續的時間。
mysql> SHOW PROFILE;
+------------------------+-----------+ | Status | Duration | +------------------------+-----------+ | (initialization) | 0.000005 | | Opening tables | 0.000033 | | System lock | 0.000037 | | Table lock | 0.000024 | | init | 0.000079 | | optimizing | 0.000024 | | statistics | 0.000079 | | preparing | 0.00003 | | Creating tmp table | 0.000124 | | executing | 0.000008 | | Copying to tmp table | 0.010048 | | Creating sort index | 0.004769 | | Copying to group table | 0.0084880 | | Sorting result | 0.001136 | | Sending data | 0.000925 | | end | 0.00001 | | removing tmp table | 0.00004 | | end | 0.000005 | | removing tmp table | 0.00001 | | end | 0.000011 | | query end | 0.00001 | | freeing items | 0.000025 | | removing tmp table | 0.00001 | | freeing items | 0.000016 | | closing tables | 0.000017 | | logging slow query | 0.000006 | +------------------------+-----------+
每行都是狀態變化的過程以及它們持續的時間。Status那一列和SHOW FULL PROCESSLIST的State應該是一致的。
這個值是來自於thd->proc_info變量。因此你所查看的這個值是直接來自MySQL內部的。盡管這些數值是比較直接易懂的，你也可以查看MySQL手冊。
你可以給SHOW PROFILES指定一個Query_ID來查看指定的語句，還可以給輸出添加新的列。如，查看用戶和CPU使用。可以用如下命令。
mysql> SHOW PROFILE CPU FOR QUERY 1;
SHOW PROFILE可以深入的查看服務器執行語句的工作情況。以及也能幫助你理解執行語句消耗時間的情況。一些限制是它沒有實現的功能，不能查看和剖析其他連接的語句，以及剖析時所引起的消耗。
SHOW PROFILES顯示最近發給服務器的多條語句，條數根據會話變量profiling_history_size定義，默認是15，最大值為100。設為0等價於關閉分析功能。
SHOW PROFILE FOR QUERY n，這裡的n就是對應SHOW PROFILES輸出中的Query_ID。
例如：
mysql> show profiles;
+----------+-------------+---------------------------------------+ | Query_ID | Duration | Query | +----------+-------------+---------------------------------------+ | 1 | 0.00037700 | alter table table1 drop column c3 int | | 2 | 70.37123800 | alter table table1 drop column c3 | | 3 | 0.00124500 | show tables | | 4 | 0.00569800 | select * from table1 where id=2 | | 5 | 0.00068500 | select count(1) from tables1 | | 6 | 0.00197900 | select count(1) from table1 | | 7 | 0.00105900 | alter table tables1 drop c1 | | 8 | 0.00800200 | alter table table1 drop c1 | +----------+-------------+---------------------------------------+ 8 rows in set (0.00 sec)
mysql> SHOW PROFILE FOR QUERY 2; #查看alter table table1 drop column c3的分析
+------------------------------+-----------+ | Status | Duration | +------------------------------+-----------+ | starting | 0.000183 | | checking permissions | 0.000057 | | checking permissions | 0.000059 | | init | 0.000060 | | Opening tables | 0.000071 | | System lock | 0.000062 | | setup | 0.000080 | | creating table | 0.005052 | | After create | 0.000220 | | copy to tmp table | 0.000244 | | rename result table | 70.364027 | | end | 0.000575 | | Waiting for query cache lock | 0.000062 | | end | 0.000075 | | query end | 0.000057 | | closing tables | 0.000061 | | freeing items | 0.000080 | | logging slow query | 0.000056 | | logging slow query | 0.000098 | | cleaning up | 0.000059 | +------------------------------+-----------+ 20 rows in set (0.00 sec)
如果沒有指定FOR QUERY，那麼輸出最近一條語句的信息。
LIMIT部分的用法與SELECT中LIMIT子句一致，不贅述。
type是可選的，取值范圍可以如下：
例：
mysql> show profile cpu for query 2;
+------------------------------+-----------+----------+------------+ | Status | Duration | CPU_user | CPU_system | +------------------------------+-----------+----------+------------+ | starting | 0.000183 | 0.000000 | 0.000000 | | checking permissions | 0.000057 | 0.000000 | 0.000000 | | checking permissions | 0.000059 | 0.000000 | 0.000000 | | init | 0.000060 | 0.000000 | 0.000000 | | Opening tables | 0.000071 | 0.000000 | 0.000000 | | System lock | 0.000062 | 0.000000 | 0.000000 | | setup | 0.000080 | 0.000000 | 0.001000 | | creating table | 0.005052 | 0.003000 | 0.001000 | | After create | 0.000220 | 0.000000 | 0.000000 | | copy to tmp table | 0.000244 | 0.000000 | 0.000000 | | rename result table | 70.364027 | 7.470864 | 41.612674 | | end | 0.000575 | 0.000000 | 0.001000 | | Waiting for query cache lock | 0.000062 | 0.000000 | 0.000000 | | end | 0.000075 | 0.000000 | 0.000000 | | query end | 0.000057 | 0.000000 | 0.000000 | | closing tables | 0.000061 | 0.000000 | 0.000000 | | freeing items | 0.000080 | 0.000000 | 0.000000 | | logging slow query | 0.000056 | 0.000000 | 0.000000 | | logging slow query | 0.000098 | 0.000000 | 0.000000 | | cleaning up | 0.000059 | 0.000000 | 0.000000 | +------------------------------+-----------+----------+------------+ 20 rows in set (0.00 sec)
ps:
SHOW PROFILE ALL FOR QUERY 2;的信息還可以通過SELECT * FROM information_schema.profiling WHERE query_id = 2 ORDER BY seq;獲取。
作用范圍
這個命令只是在本會話內起作用，即無法分析本會話外的語句。
開啟分析功能後，所有本會話中的語句都被分析（甚至包括執行錯誤的語句），除了SHOW PROFILE和SHOW PROFILES兩句本身。
應用示例：使用SHOW PROFILE分析查詢緩存命中的性能優勢。
mysql> set profiling=1;
Query OK, 0 rows affected (0.00 sec)
mysql> select count(1) as cnt from tran_excution;
+-------+ | cnt | +-------+ | 14225 | +-------+ 1 row in set (0.00 sec)
由於已經啟用了查詢緩存，相同查詢（非分區表）可以直接在查詢緩存中命中。
mysql> select count(1) as cnt from tran_excution;
我們仔細看下兩個同樣的語句的分析。
mysql> show profile source for query 1;
+--------------------------------+----------+-----------------------+---------------+-------------+ | Status | Duration | Source_function | Source_file | Source_line | +--------------------------------+----------+-----------------------+---------------+-------------+ | starting | 0.000048 | NULL | NULL | NULL | | Waiting for query cache lock | 0.000013 | try_lock | sql_cache.cc | 454 | | checking query cache for query | 0.000040 | send_result_to_client | sql_cache.cc | 1561 | | checking permissions | 0.000023 | check_access | sql_parse.cc | 4751 | | Opening tables | 0.000040 | open_tables | sql_base.cc | 4831 | | System lock | 0.000020 | mysql_lock_tables | lock.cc | 299 | | Waiting for query cache lock | 0.000037 | try_lock | sql_cache.cc | 454 | | init | 0.000020 | mysql_select | sql_select.cc | 2579 | | optimizing | 0.000015 | optimize | sql_select.cc | 865 | | statistics | 0.000017 | optimize | sql_select.cc | 1056 | | preparing | 0.000016 | optimize | sql_select.cc | 1078 | | executing | 0.000015 | exec | sql_select.cc | 1836 | | Sending data | 0.003875 | exec | sql_select.cc | 2380 | | end | 0.000018 | mysql_select | sql_select.cc | 2615 | | query end | 0.000015 | mysql_execute_command | sql_parse.cc | 4440 | | closing tables | 0.000016 | mysql_execute_command | sql_parse.cc | 4492 | | freeing items | 0.000016 | mysql_parse | sql_parse.cc | 5640 | | Waiting for query cache lock | 0.000012 | try_lock | sql_cache.cc | 454 | | freeing items | 0.000032 | NULL | NULL | NULL | | Waiting for query cache lock | 0.000017 | try_lock | sql_cache.cc | 454 | | freeing items | 0.000016 | NULL | NULL | NULL | | storing result in query cache | 0.000017 | end_of_result | sql_cache.cc | 1020 | | logging slow query | 0.000018 | log_slow_statement | sql_parse.cc | 1461 | | logging slow query | 0.000050 | log_slow_statement | sql_parse.cc | 1470 | | cleaning up | 0.000018 | dispatch_command | sql_parse.cc | 1417 | +--------------------------------+----------+-----------------------+---------------+-------------+ 25 rows in set (0.00 sec)
mysql> show profile source for query 2;
+--------------------------------+----------+-----------------------+--------------+-------------+ | Status | Duration | Source_function | Source_file | Source_line | +--------------------------------+----------+-----------------------+--------------+-------------+ | starting | 0.000051 | NULL | NULL | NULL | | Waiting for query cache lock | 0.000014 | try_lock | sql_cache.cc | 454 | | checking query cache for query | 0.000016 | send_result_to_client | sql_cache.cc | 1561 | | checking privileges on cached | 0.000013 | send_result_to_client | sql_cache.cc | 1652 | | checking permissions | 0.000015 | check_access | sql_parse.cc | 4751 | | sending cached result to clien | 0.000036 | send_result_to_client | sql_cache.cc | 1749 | | logging slow query | 0.000017 | log_slow_statement | sql_parse.cc | 1461 | | cleaning up | 0.000018 | dispatch_command | sql_parse.cc | 1417 | +--------------------------------+----------+-----------------------+--------------+-------------+ 8 rows in set (0.00 sec)
可以清晰地看到緩存中命中時，大大節省了後台的開銷。當然緩存的使用也需要根據各種場景（表的數據規模，更新頻率等）考察使用，並不是啟用緩存就一定能夠提高查詢效率。這裡僅僅作為SHOW PROFILE的一個應用示例。
