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List:       postgresql-general
Subject:    Re: REINDEX : new parameter to preserve current average leaf density as new implicit FILLFACTOR
From:       Peter Geoghegan <pg () bowt ! ie>
Date:       2019-06-26 16:09:08
Message-ID: CAH2-WzkrwRfdw82Se7SdUBivuVy9-o7zByq=p5=ZKSdz=tVdcw () mail ! gmail ! com
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On Wed, Jun 26, 2019 at 8:05 AM John Lumby <johnlumby@hotmail.com> wrote:
> > There is a very recent research paper that discusses the idea of
> > varying fillfactor with a view to ameliorating page splits:
> > 
> 
> Thanks,  I am chewing my way through that.  As you say,  it does address exactly \
> the issues I raised. Do you happen to know if their source-code is available \
> somewhere? ( I did see their db is MS SQL Server but it still might provide some \
> portable ideas. )

It's just a research paper. It might never be implemented in any system.

The point of the paper is to make page splits occur at a steady rate
after REINDEX'ing -- not to eliminate or even reduce page splits.

> > I suspect that you might find that the enhancements to B-Tree indexes
> > that went into Postgres 12 would help with this workload, especially
> > if you notice that this happens with indexes that have a lot of duplicates
> > 
> 
> I had not noticed that,   thanks for pointing it out.  Yes ,  in my workload most \
> of the indexes in question are non-unique and some have very low key card.    I \
> will try out the pg-12 beta when I get a chance.

It's easy to show problems with very low cardinality indexes in the
old code. You'll definitely notice a difference there.

> Is there a pdf or text version?

Just the talk slides:
https://www.pgcon.org/2019/schedule/attachments/518_nbtree-arch-pgcon.pdf

-- 
Peter Geoghegan


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