maria-discuss team mailing list archive

[Roberto Spadim <roberto@xxxxxxxxxxxxx>]

Hello! Only btree, no hash indexes?


2014-03-06 13:46 GMT-03:00 Sergei Golubchik <serg@xxxxxxxxxxx>:

> Hi, pslawek83!
>
> On Feb 17, pslawek83 wrote:
> > Hi Guys,
> > any comments on this issue? It seems that partial unique indexes can't
> be used in joins.
> > https://mariadb.atlassian.net/browse/MDEV-5663
>
> Please, show EXPLAIN EXTENDED (and SHOW WARNINGS after it) for this
> query of yours.
>
> > * Why the server is treating same indexes differently depends on if
> > they're UNIQUE or not
>
> It doesn't, there're almost no differences between UNIQUE and non-unique
> indexes from the optimizer point of view. Optimizer knows that for a
> unique index there can be at most one matching row (if all index parts
> are known and are NOT NULL), for non-unique indexes there can be more.
> That's basically the only difference.
>
> > * That's probably not optimizer issue, as we can't FORCE the index
>
> You cannot force the index if it is not applicable at all.
>
> > * What's internal difference between unique and non-unique index (eg.
> > memory / file representation / data structure)
>
> none.
>
> > * What each index type is suitable for, considering query optimization
> > (as there's no data i was able to find on topic)
>
> Aria only supports BTREE indexes anyway.
>
> Regards,
> Sergei
>
> _______________________________________________
> Mailing list: https://launchpad.net/~maria-discuss
> Post to     : maria-discuss@xxxxxxxxxxxxxxxxxxx
> Unsubscribe : https://launchpad.net/~maria-discuss
> More help   : https://help.launchpad.net/ListHelp
>



-- 
Roberto Spadim
SPAEmpresarial
Eng. Automação e Controle