Re: Setting pd_lower in GIN metapage

On Mon, Jun 26, 2017 at 10:54 AM, Michael Paquier
<michael(dot)paquier(at)gmail(dot)com> 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.
>
>> 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?

Good point. I think it could happen for brin meta page as well.

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center