Measuring the Query Optimizer Effect: Turning off the QO? - Mailing list pgsql-general

From Tom Mercha
Subject Measuring the Query Optimizer Effect: Turning off the QO?
Date
Msg-id AM6PR04MB5544CCC486DA6B21968A1217F4F70@AM6PR04MB5544.eurprd04.prod.outlook.com
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Responses Re: Measuring the Query Optimizer Effect: Turning off the QO?  (Rob Sargent <robjsargent@gmail.com>)
Re: Measuring the Query Optimizer Effect: Turning off the QO?  (Tom Lane <tgl@sss.pgh.pa.us>)
Re: Measuring the Query Optimizer Effect: Turning off the QO?  (Andrew Gierth <andrew@tao11.riddles.org.uk>)
List pgsql-general
Hi All

As we know, a query goes through number of stages before it is executed. 
One of these stages is query optimization (QO).

There are various parameters to try and influence optimizer decisions 
and costs. But I wanted to measure the effect of such a stage by turning 
it off completely and I can't find such a parameter which explicitly 
does that. Then I could execute a query to get the effect of "QO active 
and "QO inactive" and compare.

Obviously, I know well what the results would generally look like but I 
am just interested in measuring the differences for various types of 
queries. I am also aware that this is a simple comparison - there are 
more interesting comparisons to perform with QO tweaks, but right now I 
am interested in something basic.

So how would one shut down QO? Or at least, obtaining the guarantee of 
generating the worst plan possible, ideally without touching many 
parameters?

Best,
Tom

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