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MySQL partition table

2017.04.05

Overview

MySQL has buildin partition table support, which can help split data accross multi tables,

and provide a unified query interface as normal tables.

Benefit:

  • Easy data management: If we need to archive old data, and our table is partitioned by datetime, we can drop old partition directly.
  • Speed up query based on partition key(partitoin pruning)

Limit:

  • For partition table, every unique key must use every column in table’s partition expression(include primary key)
  • For innodb engine, paritioned table can’t have foreign key,and can’t have columns referenced by foreign keys.
  • For MyISAM engine, mysql version <= 5.6.5, DML operation will lock all partition as a whole.

Partition live db table

MySQL have several different partition type: range, list, key, hash…

For my live db table, I just want to partition it by date, one table per month.

So I choose to use range partition by the time_created column (it’s a bigint).

origin table schema:

CREATE TABLE `Record` (
    `id` bigint NOT NULL, AUTO_INCREMENT,
    `data` text DEFAULT '',
    `time_created` bigint NOT NULL,
    PRIMARY KEY (`id`)
)

After partitioning, I only want to keep recent 3 months data. If I delete rows in original table first, it will take a lot of time, also rebuild primary key and partitioning will cost many time as well.

So I decide create a new partitioned table first, and select needed data from original table to it, and do a rename operation at last.

Steps:

  • create new partiton table Record_new (with corrent primary key and partition info)
  • insert into Record_new select * from Record where id > xxx and id < yyy. (copy needed data to new table, should do it chunk by chunk since the number is huge).
  • rename table Record to Record_old, Record_new to Record.

With this flow, we can have minimum impact on live server, and can cancel at any time during copy data.

Create sql for new partition table:

CREATE TABLE `Record` (
    `id` bigint NOT NULL, AUTO_INCREMENT,
    `data` text DEFAULT '',
    `time_created` bigint NOT NULL,
    PRIMARY KEY (`id`, `time_created`)
)  PARTITION BY RANGE(time_created)
     (PARTITION p_2016 VALUES LESS THAN (UNIX_TIMESTAMP('2017-01-01')),
     PARTITION p_2017_01 VALUES LESS THAN (UNIX_TIMESTAMP('2017-02-01')),
     PARTITION p_2017_02 VALUES LESS THAN (UNIX_TIMESTAMP('2017-03-01')),
     PARTITION p_2017_03 VALUES LESS THAN (UNIX_TIMESTAMP('2017-04-01')),
     PARTITION p_2017_04 VALUES LESS THAN (UNIX_TIMESTAMP('2017-05-01')),
     PARTITION p_default VALUES LESS THAN MAXVALUE);

p_default is used to hold data if no suitable partition is available, usually, it should be null. I use a montly cronjob to reoriganize it to genearate a new partition:

ALTER TABLE Record REORGANIZE p_default into 
(PARTITION p_2017_05 VALUES LESS THAN (UNIX_TIMESTAMP('2017-06-01')),
 PARTITION p_2017_06 VALUES LESS THAN (UNIX_TIMESTAMP('2017-07-01')));

Partitoin management

Check how many rows every partitoin have:

select PARTITION_NAME,TABLE_ROWS from information_schema.partitions where table_schema='test_db' and table_name='test';

Drop partition:

ALTER TABLE Record DROP PARTITION p_xxx;
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