[TYPO3-core] RFC #13273: Bug: Caching framework sub-select is slow because mysql does not use indexes on outer query

[Christian Kuhn]

Attached v2 taking Susannes finding into account and adding a minor fix 
to the testcases to catch the error in future.

Now we need a core review :)

Regards
Christian


Christian Kuhn wrote:
> This is an SVN patch request.
> 
> Type: bugfix
> 
> BT reference: http://bugs.typo3.org/view.php?id=13273
> 
> Branches: trunk, TYPO3_4-3
> 
> Problem:
> mysql is unable to use indexes for outer query if where clause is a sub
> select [1]. This makes tag-deletion in the caching framework with db
> backend very slow on bigger tables because mysql happily decides to
> perform a full table scan.
> 
> Solution:
> Separate queries and do more logic with php.
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