Date: Thu, 18 Mar 2021 14:37:43 -0300
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Stephen Frost <sfrost@snowman.net>
Cc: Bruce Momjian <bruce@momjian.us>,
	Masahiko Sawada <sawada.mshk@gmail.com>,
	Tom Kincaid <tomjohnkincaid@gmail.com>,
	Robert Haas <robertmhaas@gmail.com>,
	Andres Freund <andres@anarazel.de>,
	Amit Kapila <amit.kapila16@gmail.com>,
	Thomas Munro <thomas.munro@gmail.com>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>,
	Masahiko Sawada <masahiko.sawada@2ndquadrant.com>
Subject: Re: Key management with tests
Message-ID: <20210318173743.GA13514@alvherre.pgsql>
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On 2021-Mar-18, Stephen Frost wrote:

> * Alvaro Herrera (alvherre@alvh.no-ip.org) wrote:
> > Patch 10 uses the term "WAL-skip relations".  What does that mean?  Is
> > it "relations that are not WAL-logged"?  I suppose we already have a
> > term for this; I'm not sure it's a good idea to invent a different term
> > that is only used in this new place.
> 
> This is discussed in src/backend/access/transam/README, specifically the
> section that talks about Skipping WAL for New RelFileNode.  Basically,
> it's the 'wal_level=minimal' optimization which allows WAL to be
> skipped.

Hmm ... that talks about WAL-skipping *changes*, not WAL-skipping
*relations*.  I thought WAL-skipping meant unlogged relations, but
I understand now that that's unrelated.  In the transam/README, WAL-skip
means a change in a transaction in a relfilenode that, if rolled back,
would disappear; and I'm not sure I understand how the code is handling
the case that a relation is under that condition.

This caught my attention because a comment says "encryption does not
support WAL-skipped relations", but there's no direct change to the
definition of RelFileNodeSkippingWAL() to account for that.  Perhaps I
am just overlooking something, since I'm just skimming anyway.

-- 
Álvaro Herrera       Valdivia, Chile