Re: query doesn't always follow 'correct' path..

On 02/18/2013 16:20, Julien Cigar wrote:
> On 02/18/2013 15:39, Bert wrote:
>> Hello,
>>
>> Thanks the nice people on irc my problem is fixed.
>> I changed the following settings in the postgres.conf file:
>> default_statistics_target = 5000 -> and I analyzed the tables after
>> the change of course -> now I only got 2 plans anymore, in stead of 3
>
> default_statistics_target = 5000 as a default is *way* too high. Such
> high values should only be set on a per-column basis ...

oops.. it's per-table and not per-column

>
>> cpu_tuple_cost = 0.1 -> by setting this value the seq scans were
>> stopped, and the better index_only scan / bitmap index scan were used
>> for this query.
>>
>> Thank you Robe and Mabe_ for helping me with this issue!
>
> s/Mabe_/Mage_ :-)
>
>>
>> wkr,
>> Bert
>>
>>
>> On Mon, Feb 18, 2013 at 2:42 PM, Bert <biertie(at)gmail(dot)com
>> <mailto:biertie(at)gmail(dot)com>> wrote:
>>
>> Hello,
>>
>> yes, the tables are vacuumed every day with the following
>> command: vacuum analyze schema.table.
>> The last statistics were collected yesterday evening. I collected
>> statistics about the statistics, and I found the following:
>> table_name; starttime; runtime
>> "st_itemseat";"2013-02-17 23:48:42";"00:01:02"
>> "st_itemseat_45";"2013-02-17 23:35:15";"00:00:08"
>> "st_itemzone";"2013-02-17 23:35:33";"00:00:01"
>>
>> st_itemseat_45 is a child-partition of st_itemseat.
>>
>> They seem to be pretty much up to date I guess?
>> I also don't get any difference in the query plans when they are
>> run in the morning, or in the evening.
>>
>> I have also run the query with set seq_scan to off, and then I
>> get the following output:
>> Total query runtime: 12025 ms.
>> 20599 rows retrieved.
>> and the following plan: http://explain.depesz.com/s/yaJK
>>
>> These are 3 different plans. And the last one is blazingly fast.
>> That's the one I would always want to use :-)
>>
>> it's also weird that this is default plan for the biggest
>> partition. But the smaller the partition gets, the smaller the
>> partition gets.
>> So I don't think it has anything to do with the memory settings.
>> Since it already chooses this plan for the bigger partitions...
>>
>> wkr,
>> Bert
>>
>>
>> On Mon, Feb 18, 2013 at 11:51 AM, Frank Lanitz
>> <frank(at)frank(dot)uvena(dot)de <mailto:frank(at)frank(dot)uvena(dot)de>> wrote:
>>
>> Am 18.02.2013 10:43, schrieb Bert:
>> > Does anyone has an idea what triggers this bad plan, and
>> how I can fix it?
>>
>> Looks a bit like wrong statistics. Are the statistiks for
>> your tables
>> correct?
>>
>> Cheers,
>> Frank
>>
>>
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>>
>>
>>
>> --
>> Bert Desmet
>> 0477/305361
>>
>>
>>
>>
>> --
>> Bert Desmet
>> 0477/305361
>
>
> --
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However, many electrons were terribly inconvenienced.