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Re: SELECT DISTINCT chooses parallel seqscan instead of indexscan on huge table with 1000 partitions

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Subject: Re: SELECT DISTINCT chooses parallel seqscan instead of indexscan on huge table with 1000 partitions
From: Dimitrios Apostolou <jimis@xxxxxxx>
Date: Mon, 13 May 2024 14:27:57 +0200 (CEST)
Cc: Tom Lane <tgl@xxxxxxxxxxxxx>, pgsql-general@xxxxxxxxxxxxxxxxxxxx
In-reply-to: <CAApHDvqWfGdUpTUp9s7AZYSeh44aLEXoBQS7UcfKM0zKhTCkiQ@mail.gmail.com>
References: <7886a68f-b466-2131-1747-f69f0fb71a37@gmx.net> <69077f15-4125-2d63-733f-21ce6eac4f01@gmx.net> <559b0e40-63e6-fa9a-6b03-d1eba10f30f8@gmx.net> <1629463.1715372568@sss.pgh.pa.us> <6a2f3906-3d7a-6924-7403-8f77d57a18e4@gmx.net> <1685688.1715391218@sss.pgh.pa.us> <CAApHDvqWfGdUpTUp9s7AZYSeh44aLEXoBQS7UcfKM0zKhTCkiQ@mail.gmail.com>
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On Sat, 11 May 2024, David Rowley wrote:

On Sat, 11 May 2024 at 13:33, Tom Lane <tgl@xxxxxxxxxxxxx> wrote:

I do kind of wonder why it's producing both a hashagg and a Unique
step --- seems like it should do one or the other.


It still needs to make the duplicate groups from parallel workers unique.


Range partitioning of the table guarantees that, since the ranges are not
overlapping.


Dimitris

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- Re: SELECT DISTINCT chooses parallel seqscan instead of indexscan on huge table with 1000 partitions
  - From: David Rowley

References:
- SELECT DISTINCT chooses parallel seqscan instead of indexscan on huge table with 1000 partitions
  - From: Dimitrios Apostolou
- Re: SELECT DISTINCT chooses parallel seqscan instead of indexscan on huge table with 1000 partitions
  - From: Dimitrios Apostolou
- Re: SELECT DISTINCT chooses parallel seqscan instead of indexscan on huge table with 1000 partitions
  - From: Dimitrios Apostolou
- Re: SELECT DISTINCT chooses parallel seqscan instead of indexscan on huge table with 1000 partitions
  - From: Tom Lane
- Re: SELECT DISTINCT chooses parallel seqscan instead of indexscan on huge table with 1000 partitions
  - From: Dimitrios Apostolou
- Re: SELECT DISTINCT chooses parallel seqscan instead of indexscan on huge table with 1000 partitions
  - From: Tom Lane
- Re: SELECT DISTINCT chooses parallel seqscan instead of indexscan on huge table with 1000 partitions
  - From: David Rowley

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