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From:Guilhem Bichot Date:November 22 2010 1:52pm
Subject:Re: bzr commit into mysql-trunk branch (jorgen.loland:3287) Bug#54641
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Jorgen Loland a écrit, Le 19.11.2010 13:19:
> #At file:///export/home/jl208045/mysql/mysql-next-mr-opt-backporting-54641-2/ based
> on revid:tor.didriksen@stripped
>  3287 Jorgen Loland	2010-11-19
>       Bug#54641: semijoin loosescan gives duplicate rows
>       The loosescan semijoin strategy does not handle join buffering 
>       on any of the tables in the loosescan range. Prior to this bug
>       fix, check_join_cache_usage() would not do join buffering on a 
>       join table if the loosescan_match_tab pointer was set for it. 
>       However, loosescan_match_tab is a pointer from the first to the 
>       last join table handled by the loosescan strategy. Join 
>       buffering could therefore be used on all join tables except 
>       the first in the loosescan range.
>       The fix is to skip join buffering if the join table is in 
>       the loosescan range, i.e., if
>       join_tab->get_sj_strategy() == SJ_OPT_LOOSE_SCAN,
>       instead of checking loosescan_match_tab.

The limitation is written in clear text in the WL which implemented 
semijoin loosescan (WL#3751):

"2.3.2 SJ-nest range, FirstMatch part
We can reuse the results of WL#3741:
  * none of the tables must use join buffering"

so there is probably nothing better to do in the scope of a bugfix, than 
properly enforcing the limitation. Ok to push.

bzr commit into mysql-trunk branch (jorgen.loland:3287) Bug#54641Jorgen Loland19 Nov
  • Re: bzr commit into mysql-trunk branch (jorgen.loland:3287) Bug#54641Guilhem Bichot22 Nov
Re: bzr commit into mysql-trunk branch (jorgen.loland:3287) Bug#54641Øystein Grøvlen24 Nov