Following on from my fun post on Where are they now: MySQL Storage Engines, I thought I’d cover the few storage engines that are really just interfaces to a collection of things. In this post, I’m talking about MERGE.

The MERGE engine was basically a multiplexer down to a number of MyISAM tables. They all had to be the same, there was no parallel query execution and it saw fairly limited use. One of the main benefits was that then you could actually put more rows in a MyISAM table than your “files up to 2/4GB” file system allowed. With the advent of partitioning, this really should have instantly gone away

https://code.launchpad.net/~stewart/drizzle/json-interface/+merge/59859

Currently a very early version of course, but it’s there in trunk if you want to play with it. Just have libcurl and libevent installed and you can submit queries via HTTP and JSON. Of course, the next steps are getting a true non-sql interface going and seeing how people go with it.

I know that MERGE isn’t everyone’s favourite storage engine but we use them quite extensively and ran into a problem the other day that I thought I’d share.

A common usage pattern is to CREATE TEMPORARY TABLE LIKE an existing MyISAM table and then ALTER TABLE to turn it into a MERGE table and specify it’s UNION. Like this:

CREATE TABLE tmpMerge LIKE a;
ALTER TABLE tmpMerge ENGINE=MERGE, UNION=(a,b);

It’s a pattern we’ve been using for ages and seems to work well in most cases.

In one application we keep aggregated data in daily tables (inspired by this article). Within the application we work out which of the daily tables we need and build them into a

One common question I get is how to use partitioning instead of MERGE tables. The process I use involves using stored procedures to create and drop partitions. This article will go over the stored procedures I use; special thanks to Roland Bouman for taking a look and giving great feedback to optimize this process.

First, a simple table, not partitioned (yet):

use test;
DROP TABLE IF EXISTS my_part;
CREATE TABLE IF NOT EXISTS my_part (
  id int NOT NULL,
  creationDate datetime NOT NULL,
  PRIMARY KEY (id,creationDate)
) ENGINE=InnoDB;

In real, life there is more to the table than just id and creationDate. The most important part is that the partitioned field(s) need to be part of the primary key.

Now, add the partition definition. This can be done in the