Zitat von azurIt <azurit AT pobox DOT sk>:

> Hi,
>
> i'm having some MySQL performance difficulties so i started to  
> search what can i do better. My table 'File' had these indexes  
> created:
> CREATE INDEX file_jobid_idx on File (JobId);
> CREATE INDEX file_jpf_idx on File (JobId, PathId, FilenameId);
>
> Which looks correct according to documentation:
> http://www.bacula.org/en/dev-manual/main/main/Catalog_Maintenance.html
>
> BUT! The first index apperas to be unneeded as it's part of the  
> second index. According to MySQL documentation, 'any leftmost prefix  
> of the index can be used by the optimizer to find row':
> http://dev.mysql.com/doc/refman/5.5/en/multiple-column-indexes.html
>
> I suggest to remove it.
>
> azur

Would also apply to PostgreSQL i guess:
http://www.postgresql.org/docs/9.2/interactive/indexes-multicolumn.html

Any comment why the additional single column index could be useful?

Regards

Andreas



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