| From: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com> |
|---|---|
| To: | Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> |
| 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 01:54:11 |
| Message-ID: | CAB7nPqQN1Gy7Z5sfqm=i0ZhE1NkDN=O=QjEqQmG5E8TFE83PuA@mail.gmail.com |
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| Lists: | pgsql-hackers |
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.
> 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.
One thing that I noticed is that this optimization could as well
happen for spgist meta pages. What do others think?
--
Michael
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