[OSM-dev] Reducing size on mediawiki server

Nick Hill nick at nickhill.co.uk
Thu Apr 12 13:06:32 BST 2007

Hello Jochen

$wgDBtransactions is unset, and defaults to false.

According to various lists, mediawiki does work fine with MyIsam.
eg: http://www.mwusers.com/forums/showthread.php?t=3472

On searching I haven't seen any evidence of show-stoppers through the type of 
inconsistency through transactions not completing with mediawiki. An issue I 
have spotted several times is loss of mediawiki through not being able to 
recover corrupt InnoDB database. I understand that except in very very rare 
situations, myisamchk will recover corrupt MyIsam tables.

I suppose this is an issue of complex vs simple. InnoDB is complex. MyIsam is 
much simpler. More like a flat file plus index.

InnoDB has built in machinery to deal with most errors in it's more complex data 
structure, but if it goes wrong, it can be almost impossible to recover. From 
the external connection point of view, InnoDB transactions will never be 
inconsistent, but the database file itself can be irretrievably inconsistent.

Jochen Topf wrote:
> Doesn't Mediawiki use transactions? I don't know enough about Mediawiki
> but would expect it to use transactions which MyIsam doesn't support.
> Can't find anything on it quickly, but there is a setting for this:
> http://www.mediawiki.org/wiki/Manual:%24wgDBtransactions
> So maybe it works ok without transactions if this is not set. I feel
> rather uneasy though when using any kind of database application without
> transactions if the application doesn't explicitly says it can work
> without them.
> Jochen

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