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From:Jonas Oreland Date:February 24 2011 11:59am
Subject:Re: bzr commit into mysql-5.1-telco-7.0 branch (ole.john.aske:4223)
Bug#11804277
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On 02/24/11 12:21, Ole John Aske wrote:
> On 23.02.2011 19:15, Jonas Oreland wrote:
>> On 02/23/11 19:07, Ole John Aske wrote:
>>> On 23.02.2011 18:00, Jonas Oreland wrote:
>>>> Hi OJ,
>>>>
>>>> 1) What do you think about using heuristic even if we don't have
> row-count.
>>>> E.g if we don't have row-count, set it to 100 and run you range-heuristic
> anyway
>>> Yes, would likely be usefull in those cases.
>> can you produce a deterministic testcase for this too...i'd be happy...
>> but i'm also ok with skipping if it's hard
> 
> I got some second thoughts here:
> 
> There are several handler methods which currently trap the 'don't have row-count'
> state. From top of my head ::records_in_range, ::info() and ::scan_time() might be
> some
> of them.
> 
> Currently 'don't have row-count' is handled by assuming 2 rows.
> 
> - Changing this to assume 100 rows for ::records_in_range() only
>    will likely cause situations where a full table scan is preferred
>    over a range which will be a performance regression.
> 
> - Changing 'unknown' to be 100 rows in all places where this is trapped
>    is likely to create lots of changed query plans and EXPLAIN's in MTR tests.
>    ... I don't think we want this either.....
> 
> So my suggestion is to don't change this and instead wait for my
> 'persistent statistics' patch which will hopefully remove all of these
> 'unknown row-count' situations.

i think changing unknown from 2 to 100...sound ok...even good (at all locations of
unknown)
and can't think of any scenario in which this would result in a poorer query plan than
what one
 can get with 2...can you ?

/Jonas
Thread
bzr commit into mysql-5.1-telco-7.0 branch (ole.john.aske:4223) Bug#11804277Ole John Aske23 Feb
  • Re: bzr commit into mysql-5.1-telco-7.0 branch (ole.john.aske:4223)Bug#11804277Jonas Oreland23 Feb
    • Re: bzr commit into mysql-5.1-telco-7.0 branch (ole.john.aske:4223)Bug#11804277Ole John Aske23 Feb
      • Re: bzr commit into mysql-5.1-telco-7.0 branch (ole.john.aske:4223)Bug#11804277Jonas Oreland23 Feb
        • Re: bzr commit into mysql-5.1-telco-7.0 branch (ole.john.aske:4223)Bug#11804277Ole John Aske24 Feb
          • Re: bzr commit into mysql-5.1-telco-7.0 branch (ole.john.aske:4223)Bug#11804277Jonas Oreland24 Feb
            • Re: bzr commit into mysql-5.1-telco-7.0 branch (ole.john.aske:4223)Bug#11804277Ole John Aske24 Feb
              • Re: bzr commit into mysql-5.1-telco-7.0 branch (ole.john.aske:4223)Bug#11804277Ole John Aske28 Feb