RE: Forced to use UNION ALL when having multiple ANY operators and ORDER BY LIMIT

[benoit <benoit@xxxxxxxxxxxxxxx>]

This new index is used but still the read is 230mb.

https://explain.dalibo.com/plan/b0f28a9e8a136afd

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De : Chris Hoover <chrish@xxxxxxxxxx>
Envoyé : lundi 12 juin 2023 22:55
À : benoit
Cc : pgsql-performance@xxxxxxxxxxxxxxxxxxxx
Objet : Re: Forced to use UNION ALL when having multiple ANY operators and ORDER BY LIMIT

 

I normally create my indexes to match the where clause of the query. While technically, it should not matter, I find a lot of time, it does.

I would create an index on (status, sender_reference, sent_at) and see if the improves your query performance.

SELECT * FROM docs WHERE status IN ('draft', 'sent') AND sender_reference IN ('Custom/1175', 'Client/362', 'Custom/280') ORDER BY sent_at DESC

Thanks,

Chris Hoover

Senior DBA

AWeber.com

Cell: (803) 528-2269

Email: chrish@xxxxxxxxxx

On Jun 12, 2023, at 4:17 PM, benoit <benoit@xxxxxxxxxxxxxxx> wrote:

Hello

I have a database with few 60gb tables. Tables rows are requested with multiple ANY or IN operators. I am not able to find an easy way to make DB able to use indexes. I often hit the index, but see a a spike of 200mb of IO or disk read.

I am using version 13 but soon 14.

I wrote a reproduction script on version 14 with plans included. https://gist.github.com/benoittgt/ab72dc4cfedea2a0c6a5ee809d16e04d

I also have plans on a snapshot of the DB with real data.

- The current query that I try to improve : https://explain.dalibo.com/plan/8b8f6e0he9feb551

  - I added the DB schema + index in query view. As you can see I have many indexes for testing purpose and try what the planner can do.

- The optimized query when I have only one ANY and migrate to UNION ALL for each parameter of the ANY operator https://explain.dalibo.com/plan/427gg053d07328ga . Query is fast as I would like but it means generate some merge to be able to get a fast result.

- The new issue I have when I have a new ANY operator on the previous optimized query. Big IO/read https://explain.dalibo.com/plan/e7ha9g637b4eh946

It seems to me quite undoable to generate for every parameters a query that will then merge. I have sometimes 3-4 ANY operators with up to 15 elements in an array.

Is there a misusage of my indexes?

Is there a limitation when using ANY or IN operators and ordered LIMIT behind?

Thanks a lot