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From:Sergei Golubchik Date:November 12 2008 12:01am
Subject:Re: bzr commit into mysql-5.1 branch (kgeorge:2703) Bug#37742
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Hi, Georgi!

On Nov 11, Georgi Kodinov wrote:
> Serg,
> On 11.11.2008, at 18:09, Sergei Golubchik wrote:
>>> When the storage engine uses secondary keys clustered with the
>>> primary key MySQL was adding the primary key parts to each secondary
>>> key.  In doing so it was not checking whether the index was on full
>>> columns and this resulted in the secondary keys being added to the
>>> list of covering keys even if they have partial columns.  Fixed by
>>> cleaning up the list of covering keys if the primary key has a
>>> partial column as a key part.
>> Could you explain please where was a bug, in the code ? What functions
>> and lines were making wrong assumptions and switching keyread mode for
>> partial keys ?
> Sure. All the keys in the keys_for_keyread (that's later assigned to 
> covering_keys) are considered covering, i.e. no read from the main table 
> was necessary. The fact that a key is in the covering_keys bitmap is a good 
> enough justification to consider it a covering key. No additional checks 
> are made if the key is a covering one.
> This information is used in several places : e.g. 
> SQL_SEELCT::test_quick_select, get_best_group_min_max, best_access_path, 
> make_join_readinfo etc.
> The actual switching to key_read is done in make_join_readinfo, 
> join_read_const_table, join_read_first, join_read_last etc.

Yes, that much I know. I asked what code was enabling keyread for
partial keys.  As you can see, in open_binary_frm() partial keys are
*not* added to keys_for_keyread bitmap. So, how comes that a keyread is
enabled for a key not present in keys_for_keyread ?

Regards / Mit vielen Grüßen,

   __  ___     ___ ____  __
  /  |/  /_ __/ __/ __ \/ /   Sergei Golubchik <serg@stripped>
 / /|_/ / // /\ \/ /_/ / /__  Principal Software Engineer/Server Architect
/_/  /_/\_, /___/\___\_\___/  Sun Microsystems GmbH, HRB München 161028
       <___/                  Sonnenallee 1, 85551 Kirchheim-Heimstetten
Geschäftsführer: Thomas Schroeder, Wolfgang Engels, Dr. Roland Boemer
Vorsitzender des Aufsichtsrates: Martin Häring
bzr commit into mysql-5.1 branch (kgeorge:2703) Bug#37742Georgi Kodinov11 Nov
  • Re: bzr commit into mysql-5.1 branch (kgeorge:2703) Bug#37742Sergei Golubchik11 Nov
Re: bzr commit into mysql-5.1 branch (kgeorge:2703) Bug#37742Sergei Golubchik12 Nov
Re: bzr commit into mysql-5.1 branch (kgeorge:2703) Bug#37742Sergei Golubchik12 Nov
Re: bzr commit into mysql-5.1 branch (kgeorge:2703) Bug#37742Sergei Golubchik25 Nov