On Wed, Feb 2, 2011 at 12:11 PM, Mladen Gogala
> Robert Haas wrote:
>> On Tue, Feb 1, 2011 It would be pretty hard to make autoanalyze work on
>> such tables
>> without removing some of the performance benefits of having such
>> tables in the first place - namely, the local buffer manager. But you
>> could ANALYZE them by hand.
> Not necessarily autoanalyze, some default rules for the situations when
> stats is not there should be put in place,
> like the following:
> 1) If there is a usable index on the temp table - use it.
> 2) It there isn't a usable index on the temp table and there is a join, make
> the temp table the first table
> in the nested loop join.
> People are complaining about the optimizer not using the indexes all over
> the place, there should be a way to
> make the optimizer explicitly prefer the indexes, like was the case with
> Oracle's venerable RBO (rules based
> optimizer). RBO didn't use statistics, it had a rank of access method and
> used the access method with the highest
> rank of all available access methods. In practice, it translated into: if an
> index exists - use it.
However, sometimes using an index results in a HORRIBLE HORRIBLE plan.
I recently encountered the issue myself, and plopping an ANALYZE
$tablename in there, since I was using a temporary table anyway, make
all the difference. The planner switched from an index-based query to
a sequential scan, and a sequential scan was (is) vastly more
efficient in this particular case.
Personally, I'd get rid of autovacuum/autoanalyze support on temporary
tables (they typically have short lives and are often accessed
immediately after creation preventing the auto* stuff from being
useful anyway), *AND* every time I ask I'm always told "make sure
ANALYZE the table before you use it".
In response to
pgsql-performance by date
|Next:||From: Robert Haas||Date: 2011-02-02 18:20:59|
|Subject: Re: [HACKERS] Slow count(*) again...|
|Previous:||From: Cesar Arrieta||Date: 2011-02-02 18:15:22|
|Subject: Server Configuration|
pgsql-hackers by date
|Next:||From: Nicolas Grilly||Date: 2011-02-02 18:20:15|
|Subject: Why "copy ... from stdio" does not return immediately when reading
|Previous:||From: Aidan Van Dyk||Date: 2011-02-02 18:14:35|
|Subject: Re: ALTER EXTENSION UPGRADE, v3|