Re: Setting pd_lower in GIN metapage

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>
Cc: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Setting pd_lower in GIN metapage
Date: 2017-09-13 04:05:19
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Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> writes:
> On 2017/09/12 23:27, Amit Kapila wrote:
>> I think one point which might be missed is that the patch needs to
>> modify pd_lower for all usages of metapage, not only when it is first
>> time initialized.

> Maybe I'm missing something, but isn't the metadata size fixed and hence
> pd_lower won't change once it's initialized? Maybe, it's not true for all
> index types?

No, the point is that you might be dealing with an index recently
pg_upgraded from v10 or before, which does not have the correct
value for pd_lower on that page. This has to be coped with.

regards, tom lane

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