[TYPO3-dev] Testing TYPO3 caching vs.[FE][pageCacheToExternalFiles]

["Marc Wöhlken [quadracom]"]

Martin Schoenbeck schrieb:
>> --------
>> When you precede a SELECT statement with the keyword EXPLAIN, MySQL
>> displays information from the optimizer about the query execution
>> _plan_. That is, MySQL explains how it _would_ process the SELECT,
>> including information about how tables are joined and in which order.
>> --------
> 
> That means, mysql will follow the explained plan as far as the plan works.
> At the point where it doesn't work any longer mysql knows, all data to
> deliver (may be none) are put together. It won't take another plan than
> that explained as long as the data aren't changed.
Explain is always a good starting point for query optimization.
It naturally can't take into account how exaclty indexes will be used.
AFAIK indexes are for example not used for disk i/o if the result
contains more than 1/3 of the total datasets as a complete read of the
corresponding db file should be faster than doing random disk acces
based on indexes.

Regards
	Marc

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Marc Wöhlken

Quadracom - Gottschall, Proffe & Wöhlken

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