Date: Mon, 15 Apr 2019 12:20:04 -0700
From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Robert Haas <robertmhaas@gmail.com>, Stephen Frost <sfrost@snowman.net>,
	Tomas Vondra <tomas.vondra@2ndquadrant.com>,
	Alvaro Herrera <alvherre@2ndquadrant.com>,
	Konstantin Knizhnik <k.knizhnik@postgrespro.ru>,
	Ashwin Agrawal <aagrawal@pivotal.io>,
	PostgreSQL mailing lists <pgsql-hackers@postgresql.org>
Subject: Re: Zedstore - compressed in-core columnar storage
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Hi,

On 2019-04-15 14:35:43 -0400, Tom Lane wrote:
> Yeah, and that's something I've regretted more than once; I think SP-GiST
> is a sterling example of something that isn't nearly useful enough in the
> real world to justify the amount of maintenance effort we've been forced
> to expend on it.  You might trawl the commit logs to get a sense of the
> amount of my own personal time --- not that of the original submitters ---
> that's gone into that one module.  Then ask yourself how much that model
> will scale, and what other more-useful things I could've accomplished
> with that time.

I do agree that the [group of] contributor's history of maintaining such
work should play a role. And I think that's doubly so with a piece as
crucial as a table AM.

But:

> We do need to limit what we accept into core PG.  I do not buy your
> argument that users expect everything to be in core.  Or more accurately,
> the people who do think that way won't be using PG anyway --- they'll
> be using MSSQL because it comes from their OS vendor.

I don't think anybody disagrees with that, actually. Including
Robert.

But I don't think it follows that we shouldn't provide things that are
either much more reasonably done in core like a pooler (authentication /
encryption; infrastructure for managing state like prepared statements,
GUCs; avoiding issues of explosion of connection counts with pooling in
other places), are required by a very significant portion of our users
(imo the case for a columnar store or a row store without the
architectural issues of heap), or where it's hard to provide the
necessary infrastructure without an in-core user (imo also the case with
columnar, due to the necessary planner / executor improvements for fast
query execution).

We also have at times pretty explicitly resisted making crucial pieces
of infrastructure usable outside of core. E.g. because it's legitimately
hard (grammar extensibility), or because we'd some concerns around
stability and the exact approach (WAL - the generic stuff is usable for
anything that wants to even be somewhat efficient, some xlog
integration).  So there's several types of extensions that one
realistically cannot do out of core, by our choice.

Greetings,

Andres Freund