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Thread: Planner choosing nested loop in place of Hashjoin

Planner choosing nested loop in place of Hashjoin

From
Praneel Devisetty
Date:
Hi,

I have a query which is taking roughly 10mins to complete and the query planner is choosing a nested loop.

query and query plan with analyze,verbose,buffers

Disabling the nested loop on session is allowing the query planner to choose a better plan and complete it in 2mins.Stats are up to date and analyze was performed a few hours ago.

Any suggestions on what is causing the planner to choose a nested loop in place of hash and how can we get the query to choose a better plan without disabling the enable_nestloopenable_nestloopenable_nestloop enable_nestloopenable_nestloop?

Thanks 
Praneel


Re: Planner choosing nested loop in place of Hashjoin

From
Samed YILDIRIM
Date:
Hi Praneel,

It is hard to propose a solution without seeing the actual query and knowing details of the tables. If I were you, I would try to increase statistics target for the columns used in joins. Default value is 100. You need to analyze those tables again after updating the statistics targets.

ALTER TABLE table ALTER COLUMN column SET STATISTICS 300;


Best regards.
Samed YILDIRIM


On Tue, 7 Mar 2023 at 14:14, Praneel Devisetty <devisettypraneel@gmail.com> wrote:
Hi,

I have a query which is taking roughly 10mins to complete and the query planner is choosing a nested loop.

query and query plan with analyze,verbose,buffers

Disabling the nested loop on session is allowing the query planner to choose a better plan and complete it in 2mins.Stats are up to date and analyze was performed a few hours ago.

Any suggestions on what is causing the planner to choose a nested loop in place of hash and how can we get the query to choose a better plan without disabling the enable_nestloopenable_nestloopenable_nestloop enable_nestloopenable_nestloop?

Thanks 
Praneel


Re: Planner choosing nested loop in place of Hashjoin

From
Jeff Janes
Date:
On Tue, Mar 7, 2023 at 7:14 AM Praneel Devisetty <devisettypraneel@gmail.com> wrote:
Hi,

I have a query which is taking roughly 10mins to complete and the query planner is choosing a nested loop.

query and query plan with analyze,verbose,buffers


What version is this?  Any chance you can share this without anonymization?  Not knowing the actual names makes it a lot harder to understand.  In particular, what is the actual function golf_romeo()? And five_two()?  And what is the regexp pattern that is bastardized into 'oscar_mike'::text ?
 
Disabling the nested loop on session is allowing the query planner to choose a better plan and complete it in 2mins.Stats are up to date and analyze was performed a few hours ago.

A lot can change in a few hours, do another analyze immediately before gathering the execution plan.  Your row estimates are dreadful, but we can't really tell why with the info provided.

Cheers,

Jeff