MySQL 5.7 SYS系統SCHEMA

標籤：

在說明系統資料庫之前，先來看下MySQL在資料字典方面的演變曆史：
MySQL4.1 提供了information_schema 資料字典。從此可以很簡單的用SQL語句來檢索需要的系統中繼資料了。
MySQL5.5 提供了performance_schema 效能字典。 但是這個字典比較專業，一般人可能也就看看就不了了之了。
MySQL5.7 提供了 sys系統資料庫。 sys資料庫裡麵包含了一系列的預存程序、自訂函數以及視圖來協助我們快速的瞭解系統的中繼資料資訊。


sys系統資料庫結合了information_schema和performance_schema的相關資料，讓我們更加容易的檢索中繼資料。 現在呢，我就示範下幾種情境下如何快速的使用。


第一，
比如之前想要知道某個表是否存在與否，可以用以下兩種方法：
A， 悲觀的方法，寫SQL從information_schema中拿資訊：

mysql> SELECT IF(COUNT(*) = 0,‘Not exists!‘,‘Exists!‘) AS ‘result‘ FROM information_schema.tables WHERE table_schema = ‘new_feature‘ AND table_name = ‘t1‘;+-------------+| result      |+-------------+| Not exists! |+-------------+1 row in set (0.00 sec)

B，樂觀的方法，假設表存在，寫一個預存程序：

DELIMITER $$USE `new_feature`$$DROP PROCEDURE IF EXISTS `sp_table_exists`$$CREATE DEFINER=`root`@`localhost` PROCEDURE `sp_table_exists`(    IN db_name VARCHAR(64),    IN tb_name VARCHAR(64),    OUT is_exists VARCHAR(60)    )BEGIN      DECLARE no_such_table CONDITION FOR 1146;      DECLARE EXIT HANDLER FOR no_such_table      BEGIN        SET is_exists = ‘Not exists!‘;      END;            SET @stmt = CONCAT(‘select 1 from ‘,db_name,‘.‘,tb_name);      PREPARE s1 FROM @stmt;      EXECUTE s1;      DEALLOCATE PREPARE s1;      SET is_exists = ‘Exists!‘;    END$$DELIMITER ;

現在來調用：

mysql> call sp_table_exists(‘new_feature‘,‘t1‘,@result);Query OK, 0 rows affected (0.00 sec)mysql> select @result;+-------------+| @result     |+-------------+| Not exists! |+-------------+1 row in set (0.00 sec)

現在我們直接用sys資料庫裡面現有的預存程序來進行調用，

mysql> CALL table_exists(‘new_feature‘,‘t1‘,@v_is_exists);Query OK, 0 rows affected (0.00 sec)mysql> SELECT IF(@v_is_exists = ‘‘,‘Not exists!‘,@v_is_exists) AS ‘result‘;+-------------+| result      |+-------------+| Not exists! |+-------------+1 row in set (0.00 sec)

第二，擷取沒有使用過的索引。

mysql> SELECT * FROM schema_unused_indexes;+---------------+-------------+--------------+| object_schema | object_name | index_name   |+---------------+-------------+--------------+| new_feature   | t1          | idx_log_time || new_feature   | t1          | idx_rank2    |+---------------+-------------+--------------+2 rows in set (0.00 sec)

第三， 檢索指定資料庫下面的表掃描資訊，過濾出執行次數大於10的查詢，

mysql> SELECT * FROM statement_analysis WHERE db=‘new_feature‘ AND full_scan = ‘*‘  AND exec_count > 10\G*************************** 1. row ***************************            query: SHOW STATUS                db: new_feature        full_scan: *       exec_count: 26        err_count: 0       warn_count: 0    total_latency: 74.68 ms      max_latency: 3.86 ms      avg_latency: 2.87 ms     lock_latency: 4.50 ms        rows_sent: 9594    rows_sent_avg: 369    rows_examined: 9594rows_examined_avg: 369    rows_affected: 0rows_affected_avg: 0       tmp_tables: 0  tmp_disk_tables: 0      rows_sorted: 0sort_merge_passes: 0           digest: 475fa3ad9d4a846cfa96441050fc9787       first_seen: 2015-11-16 10:51:17        last_seen: 2015-11-16 11:28:13*************************** 2. row ***************************            query: SELECT `state` , `round` ( SUM ... uration (summed) in sec` DESC                db: new_feature        full_scan: *       exec_count: 12        err_count: 0       warn_count: 12    total_latency: 16.43 ms      max_latency: 2.39 ms      avg_latency: 1.37 ms     lock_latency: 3.54 ms        rows_sent: 140    rows_sent_avg: 12    rows_examined: 852rows_examined_avg: 71    rows_affected: 0rows_affected_avg: 0       tmp_tables: 24  tmp_disk_tables: 0      rows_sorted: 140sort_merge_passes: 0           digest: 538e506ee0075e040b076f810ccb5f5c       first_seen: 2015-11-16 10:51:17        last_seen: 2015-11-16 11:28:132 rows in set (0.01 sec)

第四， 同樣繼續上面的，過濾出有暫存資料表的查詢，

mysql> SELECT * FROM statement_analysis WHERE db=‘new_feature‘ AND tmp_tables > 0 ORDER BY tmp_tables DESC LIMIT 1\G*************************** 1. row ***************************            query: SELECT `performance_schema` .  ... name` . `SUM_TIMER_WAIT` DESC                db: new_feature        full_scan: *       exec_count: 2        err_count: 0       warn_count: 0    total_latency: 87.96 ms      max_latency: 59.50 ms      avg_latency: 43.98 ms     lock_latency: 548.00 us        rows_sent: 101    rows_sent_avg: 51    rows_examined: 201rows_examined_avg: 101    rows_affected: 0rows_affected_avg: 0       tmp_tables: 332  tmp_disk_tables: 15      rows_sorted: 0sort_merge_passes: 0           digest: ff9bdfb7cf3f44b2da4c52dcde7a7352       first_seen: 2015-11-16 10:24:42        last_seen: 2015-11-16 10:24:421 row in set (0.01 sec)

可以看到上面查詢詳細的詳細，再也不用執行show status 手工去過濾了。




第五， 檢索執行次數排名前五的語句，

mysql> SELECT statement,total FROM user_summary_by_statement_type WHERE `user`=‘root‘ ORDER BY total DESC LIMIT 5;+-------------------+-------+| statement         | total |+-------------------+-------+| jump_if_not       | 17635 || freturn           |  3120 || show_create_table |   289 || Field List        |   202 || set_option        |   190 |+-------------------+-------+5 rows in set (0.01 sec)

樣本我就寫這麼多了，詳細的去看使用手冊並且自己摸索去吧。

MySQL 5.7 SYS系統SCHEMA