hum... did you checked only linux version, or windows too? could you provide a SQL example?
2017-01-29 14:30 GMT-02:00 AugustQ <augu...@gmx.net>: > Hi, > > by playing with the code I think I found something interesting. > > My environment: MariaDB 10.0.10, MyISAM-engine > > I played with a table-scan, no index is defined on this table. When I > execute a SQL-statement that forces the server to do a second table-scan on > a table this 2nd table-scan will be slow. > > The reason for this behaviour is the usage of a buffer: during the 1st scan > this buffer is filled, used and filled again until the whole table is > processed. At the end of the 1st scan it contains the last bytes of the > file. When a 2nd scan is started the reading of the table starts from the > beginning of the file but the buffer and all associated variables are not > reset: the buffer still contains the bytes from the end of the file, the > request cannot be fulfilled by the buffer so the request has to be handled > by reading the bytes directly from the file using the read()-function of > the Std-library. This takes much more time then simply copying the bytes > from the internal buffer. > > My idea is: somewhere in the code this situation must be detected and the > buffer (and all associated variables) reset to initial values. > reinit_io_cache() looks like the right candidate for this. > > I assume the engine Maria will show the same effect (I didn't check other > engines). > > Some questions: is my observation correct? Do you think this needs to be > fixed? Or is there no further development on this part of the code? > > Thanks > > Regards > AugustQ > > PS: you will find more details on this topic here: > http://augustq.blogspot.com/2017/01/subselect-execution-3.html > > > _______________________________________________ > Mailing list: https://launchpad.net/~maria-developers > Post to : maria-developers@lists.launchpad.net > Unsubscribe : https://launchpad.net/~maria-developers > More help : https://help.launchpad.net/ListHelp > -- Roberto Spadim SPAEmpresarial - Software ERP Eng. Automação e Controle _______________________________________________ Mailing list: https://launchpad.net/~maria-developers Post to : maria-developers@lists.launchpad.net Unsubscribe : https://launchpad.net/~maria-developers More help : https://help.launchpad.net/ListHelp
