From: Tom Lane <tgl@sss.pgh.pa.us>
To: Greg Nancarrow <gregn4422@gmail.com>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Anastasia Lubennikova <a.lubennikova@postgrespro.ru>
Cc: Peter Smith <smithpb2250@gmail.com>
Cc: Smith, Peter <peters@fast.au.fujitsu.com>
Cc: David Steele <david@pgmasters.net>
Cc: Tsunakawa, Takayuki <tsunakawa.takay@fujitsu.com>
Cc: Haribabu Kommi <kommi.haribabu@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Laurenz Albe <laurenz.albe@cybertec.at>
Cc: Dave Cramer <pg@fastcrypt.com>
Cc: Jing Wang <jingwangian@gmail.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Cc: Elvis Pranskevichus <elprans@gmail.com>
Subject: Re: Libpq support to connect to standby server as priority
Date: Tue, 05 Jan 2021 16:34:52 -0500
Message-ID: <3425296.1609882492@sss.pgh.pa.us> (raw)
In-Reply-To: <CAJcOf-e-H2VTo_0vuf69Hsh2FS4CxxWzkgDohXDGMr8cCMmurw@mail.gmail.com>
References: <20201124225917.GA21884@alvherre.pgsql>
<325979.1606259987@sss.pgh.pa.us>
<388250.1606266434@sss.pgh.pa.us>
<CAJcOf-cgj=bGOZR7F=H+Rg7846ZgC1G+xbkKKLp6zEuOnZeSFQ@mail.gmail.com>
<493358.1606322607@sss.pgh.pa.us>
<CAJcOf-emaiiPOgmpxQyAQT=DAOUPPwZ_G7Z70OdD6ZMX2ifCpw@mail.gmail.com>
<CAJcOf-e-H2VTo_0vuf69Hsh2FS4CxxWzkgDohXDGMr8cCMmurw@mail.gmail.com>
Greg Nancarrow <gregn4422@gmail.com> writes:
> Posting an updated set of patches.
I've reviewed and pushed most of v20-0001, with the following changes:
* I realized that we had more moving parts than necessary for
in_hot_standby. We don't really need two static variables, one is
sufficient --- and we shouldn't make the SHOW hook have side-effects,
that's just dangerous.
* The documentation patches were missing an addition to config.sgml,
as well as failing to list the new GUC in the two places where we
document all GUC_REPORT variables.
What I did *not* push was the change to mark transaction_read_only
as GUC_REPORT. I find that idea highly dubious, for a couple of
reasons:
* It'll create useless ParameterStatus traffic during normal operations
of an application using "START TRANSACTION READ ONLY" or the like.
* I do not think it will actually work for the desired purpose of
finding out the read-only state during session connection. AFAICS,
we don't set XactReadOnly to a meaningful value except when starting
a transaction. Yeah, we'll run a transaction during login because
we have to examine the system catalogs ... but do we start a new
one after absorbing the effects of, say, ALTER USER SET
default_transaction_read_only? I doubt it, and even if it works
today it'd be fragile, because someday somebody will try to collapse
any multiple transactions during startup into one transaction.
I think what we want to do is mark default_transaction_read_only as
GUC_REPORT, instead. That will give a reliable report of what the
state of its GUC is, and you can combine it with is_hot_standby
to decide whether the session should be considered read-only.
If you don't get those two GUC values during connection, then you
can fall back on "SHOW transaction_read_only".
Setting this back to waiting on author.
regards, tom lane
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, gregn4422@gmail.com, alvherre@alvh.no-ip.org, a.lubennikova@postgrespro.ru, smithpb2250@gmail.com, peters@fast.au.fujitsu.com, david@pgmasters.net, tsunakawa.takay@fujitsu.com, kommi.haribabu@gmail.com, robertmhaas@gmail.com, laurenz.albe@cybertec.at, pg@fastcrypt.com, jingwangian@gmail.com, elprans@gmail.com
Subject: Re: Libpq support to connect to standby server as priority
In-Reply-To: <3425296.1609882492@sss.pgh.pa.us>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox