From: Tom Lane <tgl@sss.pgh.pa.us>
To: Stephen Frost <sfrost@snowman.net>
cc: Andres Freund <andres@anarazel.de>,
        Alvaro Herrera <alvherre@2ndquadrant.com>,
        Pavan Deolasee <pavan.deolasee@gmail.com>,
        Jaime Casanova <jaime.casanova@2ndquadrant.com>,
        Haribabu Kommi <kommi.haribabu@gmail.com>,
        Tomas Vondra <tomas.vondra@2ndquadrant.com>,
        pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Patch: Write Amplification Reduction Method (WARM)
In-reply-to: <20170131222416.GS9812@tamriel.snowman.net>
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 <32115.1485901288@sss.pgh.pa.us> <20170131222416.GS9812@tamriel.snowman.net>
Comments: In-reply-to Stephen Frost <sfrost@snowman.net>
	message dated "Tue, 31 Jan 2017 17:24:17 -0500"
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Date: Tue, 31 Jan 2017 17:45:36 -0500
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Stephen Frost <sfrost@snowman.net> writes:
> * Tom Lane (tgl@sss.pgh.pa.us) wrote:
>> (I'm a little more concerned by Alvaro's apparent position that WARM
>> is a done deal; I didn't think so.  This particular change seems like
>> good cleanup anyhow, however.)

> Agreed.

BTW, the reason I think it's good cleanup is that it's something that my
colleagues at Salesforce also had to do as part of putting PG on top of a
different storage engine that had different ideas about index handling.
Essentially it's providing a bit of abstraction as to whether catalog
storage is exactly heaps or not (a topic I've noticed Robert is starting
to take some interest in, as well).  However, the patch misses an
important part of such an abstraction layer by not also converting
catalog-related simple_heap_delete() calls into some sort of
CatalogTupleDelete() operation.  It is certainly a peculiarity of
PG heaps that deletions don't require any immediate index work --- most
other storage engines would need that.

I propose that we should finish the job by inventing CatalogTupleDelete(),
which for the moment would be a trivial wrapper around
simple_heap_delete(), maybe just a macro for it.

If there's no objections I'll go make that happen in a day or two.

			regards, tom lane


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