Convert partitioned MRG_MYISAM table to Innodb

Question

I want to convert a partitioned MYISAM table (MRG_MYISAM) that has over 110 million rows (in around 60 partition tables) into Innodb.

Is there a safe way to do this? (eg Alter Table ....)

Or should I prepare a dump (which will take 10s of gigs of disk, and it might never finish)

Answer 1

I tried the example MERGE table on this page: https://dev.mysql.com/doc/refman/5.5/en/merge-storage-engine.html

CREATE TABLE `total` (
  `a` int(11) NOT NULL AUTO_INCREMENT,
  `message` char(20) DEFAULT NULL,
  KEY `a` (`a`)
) ENGINE=MRG_MyISAM DEFAULT CHARSET=utf8mb4 INSERT_METHOD=LAST UNION=(`t1`,`t2`)

And I converted it:

ALTER TABLE total ADD PRIMARY KEY (a),
  ENGINE=InnoDB
  PARTITION BY HASH(a) PARTITIONS 4;

I had to make sure there would be no duplicates in column a first.

The resulting table is:

CREATE TABLE `total` (
  `a` int(11) NOT NULL AUTO_INCREMENT,
  `message` char(20) DEFAULT NULL,
  PRIMARY KEY (`a`),
  KEY `a` (`a`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8mb4
PARTITION BY HASH (a)
PARTITIONS 4

So it still has the redundant index on column a , but otherwise it seems to have worked.

Note that this does require extra storage space. The original tables that the merge table was defined to union still exist.

mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| t1             |
| t2             |
| total          |
+----------------+

Any further changes to data in t1 , t2 will NOT become part of the total table.