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From: Laurenz Albe <[email protected]>
To: sud <[email protected]>
To: pgsql-general <[email protected]>
Subject: Re: Question on indexes
Date: Fri, 11 Oct 2024 08:43:37 +0200
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAD=mzVWLN35FHPxN0Ajh2vnDkFLyg9f0vT6EKF9uPm7CYkHS5g@mail.gmail.com>
References: <CAD=mzVWLN35FHPxN0Ajh2vnDkFLyg9f0vT6EKF9uPm7CYkHS5g@mail.gmail.com>

On Fri, 2024-10-11 at 00:19 +0530, sud wrote:
> I have never used any 'hash index' but saw documents in the past suggesting issues
> around hash index , like WAL doesnt generate for "hash index" which means we can't
> get the hash index back after crash also they are not applied to replicas etc.
> And also these indexes can not be used for range queries , for sorting etc.
> 
> However, we are seeing that one of the databases has multiple hash indexes created.
> So I wanted to understand from experts here, if it's advisable in any specific
> scenarios over B-tre despite such downsides?
> Note- Its version 15.4 database.

It is safe to use them, but in my tests I didn't find a realistic case where the were
better than a B-tree index:
https://www.cybertec-postgresql.com/en/postgresql-hash-index-performance/

Keep them if they do the trick for you, but I'd use B-tree indexes instead.

Yours,
Laurenz Albe

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