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MySql数据库表自动创建与删除分区

简述

数据库中表数据量太大时,查询速度变慢,而且在进行数据迁移时不方便。我们可以对数据量较大(超2GB)的表进行分区,以提高查询效率,方便数据维护。文章中示例了按时间对数据库表进行分区,并使用数据库存储过程与事件完成数据库表分区的自动创建与删除。

环境

  • 操作系统: Windows 7

  • 数据库:MySQL 5.7

  • 工具:Navicat for MySQL 10.1.7

数据库与表

  • 创建数据库(cma)并指定字符集(utf8)

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    CREATE DATABASE cma DEFAULT CHARSET utf8;
  • 创建表(meteorology_sensor),指定引擎(InnoDB)

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    CREATE TABLE meteorology_sensor (
    id BIGINT COMMENT '主键,自动生成' NOT NULL auto_increment,
    collected_time TIMESTAMP COMMENT '数据采集时间',
    component_id CHAR (17) COMMENT '被监测设备ID',
    device_code CHAR (17) COMMENT '设备编号' NOT NULL,
    device_id BIGINT COMMENT '设备Id',
    protocol_version CHAR (5) COMMENT '数据上传时使用的版本号,值为:v2010、v2015',
    send_state TINYINT (1) COMMENT '推送CAG状态,1 成功,0 未推送,-1 推送失败',
    air_pressure DECIMAL (10, 1) COMMENT '气压,浮点数,精确到小数点后1位,单位:hPa',
    air_temperature DECIMAL (10, 1) COMMENT '气温,浮点数,精确到小数点后1位,单位:℃',
    alarm_flag SMALLINT COMMENT '报警标识,新协议没有这个字段',
    average_wind_direction10min SMALLINT COMMENT '10分钟平均风向,无符号整数,单位:°',
    average_wind_speed10min DECIMAL (10, 1) COMMENT '十分钟平均风速,浮点数,精确到小数点后1位,单位:m/s',
    extreme_wind_speed DECIMAL (10, 1) COMMENT '极大风速,浮点数,精确到小数点后1位,单位:m/s',
    humidity SMALLINT COMMENT '湿度,无符号整数,单位:%RH',
    max_wind_speed DECIMAL (10, 1) COMMENT '最大大风速,浮点数,精确到小数点后1位,单位:m/s',
    precipitation DECIMAL (10, 1) COMMENT '降雨量,浮点数,精确到小数点后1位,单位:mm',
    precipitation_intensity DECIMAL (10, 1) COMMENT '降水强度,浮点数,精确到小数点后1位,单位:mm/min',
    radiation_intensity SMALLINT COMMENT '光辐射强度,无符号整数,单位:W/m2',
    second_time_stamp TIMESTAMP COMMENT '报文中的时间戳',
    standard_wind_speed DECIMAL (10, 1) COMMENT '标准风速,浮点数,精确到小数点后1位,单位:m/s',
    PRIMARY KEY (id)
    ) ENGINE = INNODB

注意:这里指定字符集和数据库引擎是因为项目中需要,跟分区没有关系,也可以不指定或使用其他的。

数据库表分区

添加主键

注意:分区字段必须是主键。 在这里,我们需要使用表中的时间字段(collected_time)进行分区,所以需要将其添加为主键,与原有主键(id)组成联合主键。

使用 Navicat 打开数据库,对表结构进行修改,将 collected_time 设置为主键。

或执行 SQL 语句修改表结构:

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ALTER TABLE `meteorology_sensor` DROP PRIMARY KEY ,ADD PRIMARY KEY ( `id`,`collected_time`);

初始分区

按时间范围分区,每年按季度分区,每3个月为一个分区。分区的范围应该根据实际数据量来确定,如数据量较小,可以考虑加大分区的时间范围,防止分区文件过多。

注意:最后要建一个 less than (maxvalue) 的分区(p_future),将超过设定分区时间的数据都放到这个分区里。

使用 Navicat 进行分区
  1. 设计表 -> 选项 -> 分割区

  1. 添加分区( less than )

  1. 添加最后一个分区( less than maxvalue)

  1. 确定分区后,点击确定回到设计表界面,点击 “保存” 完成分区。
使用 SQL 语句进行分区
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ALTER TABLE cma.meteorology_sensor PARTITION by RANGE (UNIX_TIMESTAMP(collected_time))
(
PARTITION p201803 VALUES less than (UNIX_TIMESTAMP('2018-04-01')),
PARTITION p201806 VALUES less than (UNIX_TIMESTAMP('2018-07-01')),
PARTITION p201809 VALUES less than (UNIX_TIMESTAMP('2018-10-01')),
PARTITION p201812 VALUES less than (UNIX_TIMESTAMP('2019-01-01')),
PARTITION p201903 VALUES less than (UNIX_TIMESTAMP('2019-04-01')),
PARTITION p_future VALUES LESS THAN (MAXVALUE)
);

查看分区文件

进入 MySQL 的数据存储目录下,查看数据库的文件,发现出现了如下的分区文件,说明初始分区正确:

创建新分区的存储过程

为了使用方便,在定义存储过程时,指定了 3 个参数,分别是:要进行分区的数据库名(p_schema)、要进行分区的表名(p_table)、要多添加的月数(p_months_to_add)。

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-- 如果存储过程已经存在,将其删除
DROP PROCEDURE IF EXISTS cma.create_new_partitions;

-- 定义创建分区的存储过程
DELIMITER $$
CREATE PROCEDURE cma.create_new_partitions(p_schema varchar(64), p_table varchar(64), p_months_to_add int)
-- 参数:
-- p_schema: 数据库名
-- p_table: 表名
-- p_months_to_add: 要多添加的月数
LANGUAGE SQL
NOT DETERMINISTIC
SQL SECURITY INVOKER
comment '给指定数据库(p_schema)的指定数据表(p_table)创建分区,分区数为当前月加上随后(p_months_to_add)个月的'
BEGIN
DECLARE done INT DEFAULT FALSE;
DECLARE current_partition_name varchar(64);
DECLARE current_partition_ts int;

-- We'll use this cursor later to check
-- whether a particular already exists.
-- @partition_name_to_add will be
-- set later.
DECLARE cur1 CURSOR FOR
SELECT partition_name
FROM information_schema.partitions
WHERE TABLE_SCHEMA = p_schema
AND TABLE_NAME = p_table
AND PARTITION_NAME != 'p_first'
AND PARTITION_NAME != 'p_future'
AND PARTITION_NAME = @partition_name_to_add;

-- We'll also use this cursor later
-- to query our temporary table.
DECLARE cur2 CURSOR FOR
SELECT partition_name, partition_range_ts
FROM partitions_to_add;

DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

DROP TEMPORARY TABLE IF EXISTS partitions_to_add;

CREATE TEMPORARY TABLE partitions_to_add (
partition_name varchar(64),
partition_range_ts int
);

SET @partitions_added = FALSE;
SET @months_ahead = 0;

-- Let's go through a loop and add each month individually between
-- the current month and the month p_months_to_add in the future.
WHILE @months_ahead <= p_months_to_add DO
-- We figure out what the correct month is by adding the
-- number of months to the current date
SET @date = CURDATE();
SET @q = 'SELECT DATE_ADD(?, INTERVAL ? MONTH) INTO @month_to_add';
PREPARE st FROM @q;
EXECUTE st USING @date, @months_ahead;
DEALLOCATE PREPARE st;
SET @months_ahead = @months_ahead + 1;

-- Then we format the month in the same format used
-- in our partition names.
SET @q = 'SELECT DATE_FORMAT(@month_to_add, ''%Y%m'') INTO @formatted_month_to_add';
PREPARE st FROM @q;
EXECUTE st;
DEALLOCATE PREPARE st;

-- And then we use the formatted date to build the name of the
-- partition that we want to add. This partition name is
-- assigned to @partition_name_to_add, which is used in
-- the cursor declared at the start of the procedure.
SET @q = 'SELECT CONCAT(''p'', @formatted_month_to_add) INTO @partition_name_to_add';
PREPARE st FROM @q;
EXECUTE st;
DEALLOCATE PREPARE st;

SET done = FALSE;
SET @first = TRUE;

-- And then we loop through the results returned by the cursor,
-- and if a row already exists for the current partition,
-- then we do not need to create the partition.
OPEN cur1;

read_loop: LOOP
FETCH cur1 INTO current_partition_name;

-- The cursor returned 0 rows, so we can create the partition.
IF done AND @first THEN
SELECT CONCAT('Creating partition: ', @partition_name_to_add);

-- Now we need to get the end date of the new partition.
-- Note that the date is for the non-inclusive end range,
-- so we actually need the date of the first day of the *next* month.

-- First, let's get a date variable for the first of the partition month
SET @q = 'SELECT DATE_FORMAT(@month_to_add, ''%Y-%m-01 00:00:00'') INTO @month_to_add';
PREPARE st FROM @q;
EXECUTE st;
DEALLOCATE PREPARE st;

-- Then, let's add 1 month
SET @q = 'SELECT DATE_ADD(?, INTERVAL 1 MONTH) INTO @partition_end_date';
PREPARE st FROM @q;
EXECUTE st USING @month_to_add;
DEALLOCATE PREPARE st;

-- We need the date in UNIX timestamp format.
SELECT UNIX_TIMESTAMP(@partition_end_date) INTO @partition_end_ts;

-- Now insert the information into our temporary table
INSERT INTO partitions_to_add VALUES (@partition_name_to_add, @partition_end_ts);
SET @partitions_added = TRUE;
END IF;

-- Since we had at least one row returned, we know the
-- partition already exists.
IF ! @first THEN
LEAVE read_loop;
END IF;

SET @first = FALSE;
END LOOP;

CLOSE cur1;
END WHILE;

-- Let's actually add the partitions now.
IF @partitions_added THEN
-- First we need to build the actual ALTER TABLE query.
SET @schema = p_schema;
SET @table = p_table;
SET @q = 'SELECT CONCAT(''ALTER TABLE '', @schema, ''.'', @table, '' REORGANIZE PARTITION p_future INTO ( '') INTO @query';
PREPARE st FROM @q;
EXECUTE st;
DEALLOCATE PREPARE st;

SET done = FALSE;
SET @first = TRUE;

OPEN cur2;

read_loop: LOOP
FETCH cur2 INTO current_partition_name, current_partition_ts;

IF done THEN
LEAVE read_loop;
END IF;

-- If it is not the first partition,
-- then we need to add a comma
IF ! @first THEN
SET @q = 'SELECT CONCAT(@query, '', '') INTO @query';
PREPARE st FROM @q;
EXECUTE st;
DEALLOCATE PREPARE st;
END IF;

-- Add the current partition
SET @partition_name = current_partition_name;
SET @partition_ts = current_partition_ts;
SET @q = 'SELECT CONCAT(@query, ''PARTITION '', @partition_name, '' VALUES LESS THAN ('', @partition_ts, '')'') INTO @query';
PREPARE st FROM @q;
EXECUTE st;
DEALLOCATE PREPARE st;

SET @first = FALSE;
END LOOP;

CLOSE cur2;

-- We also need to include the p_future partition
SET @q = 'SELECT CONCAT(@query, '', PARTITION p_future VALUES LESS THAN (MAXVALUE))'') INTO @query';
PREPARE st FROM @q;
EXECUTE st;
DEALLOCATE PREPARE st;

-- And then we prepare and execute the ALTER TABLE query.
PREPARE st FROM @query;
EXECUTE st;
DEALLOCATE PREPARE st;
END IF;

DROP TEMPORARY TABLE partitions_to_add;
END$$
DELIMITER ;

创建删除分区存储过程

同样的,为了使用方便,在定义删除分区的存储过程时也指定了几个参数,分别是:数据库名(p_schema)、表名(p_table)、保留的分区数(p_months_to_keep)、删除分区等待时间(p_seconds_to_sleep)。

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-- 如果存储过程已经存在,将其删除
DROP PROCEDURE IF EXISTS cma.drop_old_partitions;

-- 定义删除分区的存储过程
DELIMITER $$
CREATE PROCEDURE cma.drop_old_partitions(p_schema varchar(64), p_table varchar(64), p_months_to_keep int, p_seconds_to_sleep int)
-- 参数:
-- p_schema: 数据库名
-- p_table: 数据库表名
-- p_months_to_keep: 保留的分区数
-- p_seconds_to_sleep: 删除分区时等待时间,单位:秒
LANGUAGE SQL
NOT DETERMINISTIC
SQL SECURITY INVOKER
comment '删除指定数据库(p_schema)的指定数据表(p_table)的老分区,保留的分区数为(p_months_to_keep) +1 个,每次删除分区时会等待(p_seconds_to_sleep)秒'
BEGIN
DECLARE done INT DEFAULT FALSE;
DECLARE current_partition_name varchar(64);

-- We'll use this cursor later to get
-- the list of partitions to drop.
-- @last_partition_name_to_keep will be
-- set later.
DECLARE cur1 CURSOR FOR
SELECT partition_name
FROM information_schema.partitions
WHERE TABLE_SCHEMA = p_schema
AND TABLE_NAME = p_table
AND PARTITION_NAME != 'p_first'
AND PARTITION_NAME != 'p_future'
AND PARTITION_NAME < @last_partition_name_to_keep;

DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

-- Now we get the last month of data that we want to keep
-- by subtracting p_months_to_keep from the current date.
-- Note that it will actually keep p_months_to_keep+1 partitions,
-- since the current month is not complete.
SET @date = CURDATE();
SET @months_to_keep = p_months_to_keep;
SET @q = 'SELECT DATE_SUB(?, INTERVAL ? MONTH) INTO @last_month_to_keep';
PREPARE st FROM @q;
EXECUTE st USING @date, @months_to_keep;
DEALLOCATE PREPARE st;

-- Then we format the last month in the same format used
-- in our partition names.
SET @q = 'SELECT DATE_FORMAT(@last_month_to_keep, ''%Y%m'') INTO @formatted_last_month_to_keep';
PREPARE st FROM @q;
EXECUTE st;
DEALLOCATE PREPARE st;

-- And then we use the formatted date to build the name of the
-- last partition that we want to keep. This partition name is
-- assigned to @last_partition_name_to_keep, which is used in
-- the cursor declared at the start of the procedure.
SET @q = 'SELECT CONCAT(''p'', @formatted_last_month_to_keep) INTO @last_partition_name_to_keep';
PREPARE st FROM @q;
EXECUTE st;
DEALLOCATE PREPARE st;

SELECT CONCAT('Dropping all partitions before: ', @last_partition_name_to_keep);

SET @first = TRUE;

-- And then we loop through all partitions returned by the cursor,
-- and those partitions are dropped.
OPEN cur1;

read_loop: LOOP
FETCH cur1 INTO current_partition_name;

IF done THEN
LEAVE read_loop;
END IF;

IF ! @first AND p_seconds_to_sleep > 0 THEN
SELECT CONCAT('Sleeping for ', p_seconds_to_sleep, ' seconds');
SELECT SLEEP(p_seconds_to_sleep);
END IF;

SELECT CONCAT('Dropping partition: ', current_partition_name);

-- First we build the ALTER TABLE query.
SET @schema = p_schema;
SET @table = p_table;
SET @partition = current_partition_name;
SET @q = 'SELECT CONCAT(''ALTER TABLE '', @schema, ''.'', @table, '' DROP PARTITION '', @partition) INTO @query';
PREPARE st FROM @q;
EXECUTE st;
DEALLOCATE PREPARE st;

-- And then we prepare and execute the ALTER TABLE query.
PREPARE st FROM @query;
EXECUTE st;
DEALLOCATE PREPARE st;

SET @first = FALSE;
END LOOP;

CLOSE cur1;

-- If no partitions were dropped, then we can also skip this.
IF ! @first THEN
-- Then we need to get the date of the new first partition.
-- We need the date in UNIX timestamp format.
SET @q = 'SELECT DATE_FORMAT(@last_month_to_keep, ''%Y-%m-01 00:00:00'') INTO @new_first_partition_date';
PREPARE st FROM @q;
EXECUTE st;
DEALLOCATE PREPARE st;
SELECT UNIX_TIMESTAMP(@new_first_partition_date) INTO @new_first_partition_ts;

-- We also need to get the date of the second partition
-- since the second partition is also needed for REORGANIZE PARTITION.
SET @q = 'SELECT DATE_ADD(@new_first_partition_date, INTERVAL 1 MONTH) INTO @second_partition_date';
PREPARE st FROM @q;
EXECUTE st;
DEALLOCATE PREPARE st;
SELECT UNIX_TIMESTAMP(@second_partition_date) INTO @second_partition_ts;

SELECT CONCAT('Reorganizing first and second partitions. first partition date = ', @new_first_partition_date, ', second partition date = ', @second_partition_date);

-- Then we build the ALTER TABLE query.
SET @schema = p_schema;
SET @table = p_table;
SET @q = 'SELECT CONCAT(''ALTER TABLE '', @schema, ''.'', @table, '' REORGANIZE PARTITION p_first, '', @last_partition_name_to_keep, '' INTO ( PARTITION p_first VALUES LESS THAN ( '', @new_first_partition_ts, '' ), PARTITION '', @last_partition_name_to_keep, '' VALUES LESS THAN ( '', @second_partition_ts, '' ) ) '') INTO @query';
PREPARE st FROM @q;
EXECUTE st;
DEALLOCATE PREPARE st;

-- And then we prepare and execute the ALTER TABLE query.
PREPARE st FROM @query;
EXECUTE st;
DEALLOCATE PREPARE st;
END IF;
END$$
DELIMITER ;

创建删除老分区并创建新分区的存储过程

为了能够实现自动的删除老分区和创建新分区,定义一个存储过程,调用上面定义的两个存储过程,传入上面两个存储过程需要的参数:数据库名(p_schema)、表名(p_table)、要多添加的月数(p_months_to_add)、保留的分区数(p_months_to_keep)、删除分区等待时间(p_seconds_to_sleep)。

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-- 如果存储过程已经存在,将其删除
DROP PROCEDURE IF EXISTS cma.perform_partition_maintenance;

-- 定义删除老分区并创建新分区的存储过程
DELIMITER $$
CREATE PROCEDURE cma.perform_partition_maintenance(p_schema varchar(64), p_table varchar(64), p_months_to_add int, p_months_to_keep int, p_seconds_to_sleep int)
-- 先删除老的分区,再生成新的分区
-- 参数:p_chema: 数据库名;
-- p_table: 数据表名;
-- p_months_to_add: 创建分区时,添加的分区数量,例如:当值为0时,只会创建当前月的分区,当值为2时,会创建当前月和后2个月的分区;
-- p_months_to_keep: 删除分区时, 保留的分区数量,保留的分区数会多1,例如:当值为3时,会保留4个分区;
-- p_seconds_to_sleep: 删除分区时,等待删除的时间,单位:秒;
LANGUAGE SQL
NOT DETERMINISTIC
SQL SECURITY INVOKER
comment '指定数据库(p_schema)的指定数据表(p_table),先删除老分区,再创建新分区,删除时保留的分区数为(p_months_to_keep) +1 个,每次删除分区时会等待(p_seconds_to_sleep)秒,创建的新分区数为当前月加上随后(p_months_to_add)个月的'
BEGIN
CALL cma.drop_old_partitions(p_schema, p_table, p_months_to_keep, p_seconds_to_sleep);
CALL cma.create_new_partitions(p_schema, p_table, p_months_to_add);
END$$
DELIMITER ;

创建定时执行的事件

创建定时事件:从现在时间开始,每隔一个月触发一次,将调用上面写的存储过程,完成自动删除老的分区,创建新的分区,修改事件中调用存储过程的参数,即可完成对其他表的自动分区管理。

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-- 如果事件已经存在,将其删除  
DROP EVENT if EXISTS cma.monthly_event_meteorology_sensor;

-- 创建定时事件:从现在时间开始,每隔一个月触发一次,将调用上面写的存储过程,完成自动删除老的分区,创建新的分区
CREATE EVENT cma.monthly_event_meteorology_sensor
ON SCHEDULE
EVERY 1 MONTH
STARTS NOW()
COMMENT '微气象数据,从现在开始,每月定时删除分区、创建新分区'
DO
CALL cma.perform_partition_maintenance('cma', 'meteorology_sensor', 3, 6, 5);

扩展

MySQL 中其它分区方式

在上面的示例中,我们按字段值的范围(RANGE)进行分区,在 MySQL 中还提供的分区方式:

  • 范围分区(RANGE): 按连续的区间范围把数据分到不同分区中,要求分区范围不能重叠,而且必须连续,常见的有按时间、自增的id进行分区。

  • 列表分区(LIST): 按枚举出的值进行分区,如按地理位置不同将数据分到不同区,东北、华北、华南…。

  • 散列分区(HASH): 基于给定的分区数,通过用户定义的计算后,将数据分到不同分区。这个函数可以包含MySQL 中有效的、产生非负整数值的任何表达式。

  • 键分区(KEY): 类似 HASH 分区,区别在于 KEY 分区只支持一列或多列,且MySQL服务器提供其自身的哈希函数。必须有一列或多列包含整数值。

  • 线性散列分区(LINEAR_HASH): 与常规哈希的区别在于,线性哈希功能使用的一个线性的2的幂(powers-of-two)运算法则,而常规哈希使用的是求哈希函数值的模数

  • 线性键(LINEAR_KEY): 与常规 KEY 的区别也是使用的一个线性的2的幂(powers-of-two)运算法则。

注意事项

  • 作为分区的字段需要设置为外键,否则无法分区。

  • 被分区的表中不能有外键,否则无法分区,分区时 mysql 会报 1506 错误。

  • 当使用 range 方式分区且最后一个分区为 less than maxvalue 时,手动添加新分区时,不能直接添加,会报 1481 错误(MAXVALUE can only be used in last partition definition),需要将 future 分区分割成两个分区,可执行如下 sql 语句:

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    -- 将 battery_state 表中 future 分区重新划分,得到两个分区:p201906、future
    ALTER TABLE battery_state REORGANIZE PARTITION future INTO(
    PARTITION p201906 VALUES less than (UNIX_TIMESTAMP('2019-07-01')) ENGINE = InnoDB,
    PARTITION future VALUES less than MAXVALUE ENGINE = InnoDB
    );
  • 如果想要合并两个分区,可以使用如下 SQL:

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    -- 合并最后一个分区和 future 分区
    ALTER TABLE battery_state REORGANIZE PARTITION p202112,future INTO (PARTITION future VALUES less than MAXVALUE);
    -- 合并两个分区,注意最后面使用函数获得时间戳的地方要用括号括起来,否则会报错
    ALTER TABLE battery_state REORGANIZE PARTITION p202102,p202104 INTO (PARTITION p202104 VALUES less than (UNIX_TIMESTAMP('2021-05-01')));

参考资料

总结

最后,由于作者水平有限,文章中内容如有疏漏或错误之处,还请各位读者不吝指正!