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Re: Some big databases and merge
Posted by: Ingo Strüwing
Date: June 08, 2006 01:08PM

Hi,

MERGE makes no assumptions about the contents of the MyISAM tables. It simply has no idea if certain keys can be in one or a few tables only. Hence for index accesses, every MyISAM table is scanned in sequence. Even UNIQUE indexes don't help as a key could exist once in every MyISAM table.

However, it is no big deal for a MyISAM table to tell if there are keys in an index range or not. So the scanning of tables without matching keys is fast.

I'm no VIEW expert, but I doubt that you can accomplish what you want by using views.

I suggest to exchange MERGE sub-tables in an interval that is convenient for administration. In terms of performance I think you should not have too many sub-tables, but also not too big sub-tables. But exact numbers depend so much on the application that I don't dare to say more.

Regards

Ingo Strüwing, Senior Software Developer - Storage Engines
MySQL AB, www.mysql.com

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