Re: Setting pd_lower in GIN metapage

From: Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>
To: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>
Cc: Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Setting pd_lower in GIN metapage
Date: 2017-06-26 06:54:07
Message-ID: 4880dfb1-3acb-f4f4-9233-e5129acc8ecd@lab.ntt.co.jp
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On 2017/06/26 10:54, Michael Paquier wrote:
> On Fri, Jun 23, 2017 at 11:17 AM, Amit Langote
> <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>> That was it, thanks for the pointer.
>
> GinInitMetabuffer() sets up pd_lower and pd_upper anyway using
> PageInit so the check of PageIsVerified is guaranteed to work in any
> case. Upgraded pages will still have their pd_lower set to the
> previous values, and new pages will have the optimization. So this
> patch is actually harmless for past pages, while newer ones are seen
> as more compressible.

Right.

>> Attached updated patch, which I confirmed, passes wal_consistency_check = gin.
>
> I have spent some time looking at this patch, playing with pg_upgrade
> to check the state of the page upgraded. And this looks good to me.

Thanks for the review.

> One thing that I noticed is that this optimization could as well
> happen for spgist meta pages. What do others think?

I agree. As Sawada-san mentioned, brin metapage code can use a similar patch.

So attached are three patches for gin, brin, and sp-gist respectively.
Both brin and sp-gist cases didn't require any special consideration for
passing wal_consistency_checking, as the patch didn't cause brin and
sp-gist metapages to become invalid when recreated on standby (remember
that patch 0001 needed to be updated for that).

Thanks,
Amit

Attachment Content-Type Size
0001-Set-pd_lower-correctly-in-the-GIN-metapage.patch text/plain 2.6 KB
0002-Set-pd_lower-correctly-in-the-BRIN-index-metapage.patch text/plain 963 bytes
0003-Set-pd_lower-correctly-in-the-SP-GiST-index-metapage.patch text/plain 989 bytes

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