結合前2天的內容，今天會實作資料分區刪除&建立event呼叫我們寫好的procedure達到我們的需求。

• 情境模擬

有一個尚未切分區的資料表act，且本身已經有資料在內了，想用該表欄位created_at(建立時間)當做partition key切表，除了切分區還要能達到自動新增分區與刪除舊資料分區的動作，方便資料上的維護。

• 刪除x天前歷史分區。

  概念: 取表分區最小值與今天日期相比，看需要保留幾天。

• 實作流程

DELIMITER ||  
DROP PROCEDURE IF EXISTS del_part ||  
CREATE PROCEDURE del_part(IN_SCHEMANAME VARCHAR(64), IN_TABLENAME VARCHAR(64),IN_DELETE INT)
BEGIN   

DECLARE n_sysdate date; 
DECLARE min_partition_day date;
DECLARE del_partition_name VARCHAR(255) ;

--取最小分區值
select from_unixtime(partition_description) into min_partition_day from information_schema.partitions where table_schema = IN_SCHEMANAME  and table_name = IN_TABLENAME AND partition_description < 'MAXVALUE' order by partition_description asc limit 1;

set n_sysdate = sysdate();

--判斷要刪除天數的參數執行刪除分區作業
WHILE min_partition_day <= (n_sysdate - INTERVAL IN_DELETE DAY) DO

	SET del_partition_name = date_format(min_partition_day - INTERVAL 1 DAY,'p%Y%m%d');

	SET @sql = concat('alter table ', IN_SCHEMANAME, '.', IN_TABLENAME, ' drop partition ', del_partition_name);
	SELECT @sql;
	PREPARE stmt FROM @sql;
	EXECUTE stmt;
	DEALLOCATE PREPARE stmt;

	SET min_partition_day = min_partition_day + INTERVAL 1 DAY;

END WHILE;

SET @STEP = "STEP: drop partition [ PASS ]";
SELECT @STEP; 

END || 
DELIMITER ;

• 執行刪除舊資料分區步驟

CALL del_part('t7','act',7);

假設我們要刪除前7天之前的分區 (這邊等於會刪除掉p20210924分區)

完成後就可以看到分區＆分區中的資料一併被刪除了

最後結合全部內容成一個procedure方便呼叫～

• 完整自動分區實作procedure

DELIMITER ||  
DROP PROCEDURE IF EXISTS auto_part ||  
CREATE PROCEDURE auto_part(IN_SCHEMANAME VARCHAR(64), IN_TABLENAME VARCHAR(64),IN_CREATE INT,IN_DELETE INT)
BEGIN   

DECLARE isexist_partition varchar(255) default ''; 
DECLARE old_date VARCHAR(255);
DECLARE new_p_description VARCHAR(255);
DECLARE new_p_name VARCHAR(255);

DECLARE n_sysdate date; 
DECLARE max_partition_day date; 
DECLARE p_name VARCHAR(255) ;
DECLARE p_description VARCHAR(255) ;

DECLARE min_partition_day date; 
DECLARE del_partition_name VARCHAR(255) ;


select partition_name into isexist_partition from information_schema.partitions where table_schema = IN_SCHEMANAME  and table_name = IN_TABLENAME limit 1;

IF isexist_partition <=> NULL THEN 
	SET @p_check = "The table has no partition。 STEP: Add table partition";
    SELECT @p_check;

	select date(from_unixtime(`created_at`)) into old_date  from `act` order by `created_at` asc limit 1 ;
	SET old_date = REPLACE(old_date, '-', ''); 

	SET new_p_name = DATE_FORMAT(old_date, 'p%Y%m%d');
	SET new_p_description = unix_timestamp(old_date + INTERVAL 1 DAY);
	SET @SQL = CONCAT('ALTER TABLE `', IN_SCHEMANAME, '`.`', IN_TABLENAME, '`', ' PARTITION BY RANGE (`created_at`) (PARTITION ', new_p_name, ' VALUES LESS THAN (', new_p_description, '),PARTITION pmax VALUES LESS THAN MAXVALUE );');	
	SELECT @SQL;
    PREPARE stmt FROM @SQL;
    EXECUTE stmt;
    DEALLOCATE PREPARE stmt;

END IF;

SET @STEP = "STEP: check partition [ PASS ]";
SELECT @STEP; 

set n_sysdate = sysdate();

select from_unixtime(partition_description) into max_partition_day from information_schema.partitions where table_schema = IN_SCHEMANAME  and table_name = IN_TABLENAME AND partition_description < 'MAXVALUE' order by partition_description desc limit 1;

WHILE max_partition_day <= (n_sysdate + INTERVAL IN_CREATE DAY) DO

	SET p_name = date_format(max_partition_day ,'p%Y%m%d');
	SET p_description = unix_timestamp(max_partition_day + INTERVAL 1 DAY);

	SET @sql = concat('ALTER TABLE ', IN_SCHEMANAME, '.', IN_TABLENAME, ' REORGANIZE PARTITION `pmax` INTO  (partition ', p_name, ' values less than (', p_description, '),PARTITION `pmax` VALUES LESS THAN MAXVALUE )');
	SELECT @sql;
	PREPARE stmt FROM @sql;
	EXECUTE stmt;
	DEALLOCATE PREPARE stmt;

	SET max_partition_day = max_partition_day + INTERVAL 1 DAY;

END WHILE;

SET @STEP = "STEP: add historical date to today [ PASS ]";
SELECT @STEP; 


select from_unixtime(partition_description) into min_partition_day from information_schema.partitions where table_schema = IN_SCHEMANAME  and table_name = IN_TABLENAME AND partition_description < 'MAXVALUE' order by partition_description asc limit 1;

WHILE min_partition_day <= (n_sysdate - INTERVAL IN_DELETE DAY) DO

	SET del_partition_name = date_format(min_partition_day - INTERVAL 1 DAY,'p%Y%m%d');

	SET @sql = concat('alter table ', IN_SCHEMANAME, '.', IN_TABLENAME, ' drop partition ', del_partition_name);
	SELECT @sql;
	PREPARE stmt FROM @sql;
	EXECUTE stmt;
	DEALLOCATE PREPARE stmt;

	SET min_partition_day = min_partition_day + INTERVAL 1 DAY;

END WHILE;

SET @STEP = "STEP: drop partition [ PASS ]";
SELECT @STEP; 

END || 
DELIMITER ;

• 執行完整自動表分區異動

CALL auto_part('t7','act',5,7);

內容:

1. 使用test.act資料表created_at 整數型態欄位當partition key進行分區作業。

2. 預先建立後5天分區。

3. 資料維護上只保留到7天前的資料。

最後有了寫好的程式碼，要讓程序在特定時間固定執行就可以使用mysql Event排成的功能來實現。

如何設定event內容!? MYSQL EVENT用法

1. 先看事件排成有無開啟

mysql> show variables like 'event_scheduler';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| event_scheduler | OFF   |
+-----------------+-------+
1 row in set (0.01 sec)

2. 設定參數為 ON

--重啟後失效
set global event_scheduler = on;

--修改設定檔 my.cnf
event_scheduler = 1

• 建立呼叫procrdure的排程事件

DELIMITER || 
CREATE EVENT IF NOT EXISTS `auto_act_event` --建立事件＆確認event是否存在，存在則不建立
ON SCHEDULE EVERY 1 day  --指定為循環事件(每天執行)
STARTS '2021-10-02 20:00:00'  --START / END 用來指定事件有效開始結束時間。ps.這邊因為要持續跑所以只設定事件開始執行時間。
ON COMPLETION PRESERVE --避免事件在到期後自動刪除
ENABLE
COMMENT 'act_event_partition'  
DO BEGIN    --執行內容區塊
	call auto_part('t7','act',5,7);
END||
DELIMITER ;

• 相關使用Event內容

--查詢資料庫存在哪些event
SHOW EVENTS FROM db_name;

--查詢event建立結構
SHOW CREATE EVENT event_name;

--刪除現有的事件
DROP EVENT IF EXISTS event_name;

到這邊我們就完整的實現自動切表的維護作業了