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Re: Shouldn't we have a way to avoid "risky" plans?

From: Vitalii Tymchyshyn <tivv00(at)gmail(dot)com>
To: Merlin Moncure <mmoncure(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Claudio Freire <klaussfreire(at)gmail(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, postgres performance list <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Shouldn't we have a way to avoid "risky" plans?
Date: 2011-03-25 09:43:14
Message-ID: 4D8C63B2.1060800@gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
24.03.11 20:41, Merlin Moncure написав(ла):
> 2011/3/24 Віталій Тимчишин<tivv00(at)gmail(dot)com>:
>>
>> This can se GUC-controllable. Like plan_safety=0..1 with low default value.
>> This can influence costs of plans where cost changes dramatically with small
>> table changes and/or statistics is uncertain. Also this can be used as
>> direct "hint" for such dangerous queries by changing GUC for session/single
>> query.
> ISTM if you add statistics miss and 'risk margin' to the things the
> planner would have to consider while generating a plan, you are
> greatly increasing the number of plan paths that would have to be
> considered for any non trivial query.
Why so? I simply change cost estimation functions. This won't change 
number of pathes.

Best regards, Vitalii Tymchyshyn.

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