On 7/7/19 6:49 PM, Tom Mercha wrote:On 08/07/2019 01:46, Rob Sargent wrote:On Jul 7, 2019, at 5:22 PM, Tom Mercha <mercha_t@xxxxxxxxxxx> wrote: 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, TomDrop all indices?Sorry, maybe my question wasn't clear enough. A query can be rewritten in various ways by applying rules and costs of relational algebra operators, as well as their parallelisation. I am talking about turning off this query optimization, so I am already assuming that indexes aren't present. It seems as though you're asking what the "First Approximation" plan is, before it tries to get Too Clever. However, I don't think there's a separation between Query Planner and Query Optimizer. https://www.postgresql.org/docs/9.6/planner-optimizer.html --
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