Date: Tue, 24 Nov 2020 19:59:17 -0300
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Anastasia Lubennikova <a.lubennikova@postgrespro.ru>,
	Greg Nancarrow <gregn4422@gmail.com>,
	Peter Smith <smithpb2250@gmail.com>,
	"Smith, Peter" <peters@fast.au.fujitsu.com>,
	David Steele <david@pgmasters.net>,
	"Tsunakawa, Takayuki" <tsunakawa.takay@fujitsu.com>,
	Haribabu Kommi <kommi.haribabu@gmail.com>,
	Robert Haas <robertmhaas@gmail.com>,
	Laurenz Albe <laurenz.albe@cybertec.at>,
	Dave Cramer <pg@fastcrypt.com>, Jing Wang <jingwangian@gmail.com>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>,
	Elvis Pranskevichus <elprans@gmail.com>
Subject: Re: Libpq support to connect to standby server as priority
Message-ID: <20201124225917.GA21884@alvherre.pgsql>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <311787.1606254559@sss.pgh.pa.us>
User-Agent: Mutt/1.10.1 (2018-07-13)
Precedence: bulk

On 2020-Nov-24, Tom Lane wrote:

> I'm inclined to go ahead and commit the 0001 patch I posted at [1]
> (ie, change the implementation of GUC_REPORT to avoid intra-query
> reports), since that addresses a performance problem that's
> independent of the goal here.  The rest of this seems to still
> be in Greg's court.

Sounded a good idea to me.

> Has anyone got an opinion about the further improvement I suggested:
> 
> >> As it stands, 0001 reduces the ParameterStatus message traffic to
> >> at most one per GUC per query, but it doesn't attempt to eliminate
> >> duplicate ParameterStatus messages altogether.  We could do that
> >> as a pretty simple adjustment if we're willing to expend the storage
> >> to remember the last value sent to the client.  It might be worth
> >> doing, since for example the function-SET-clause case would typically
> >> lead to no net change in the GUC's value by the end of the query.
> 
> On reflection this seems worth doing, since excess client traffic
> is far from free.

Agreed.  If this is just a few hundred bytes of server-side local memory
per backend, it seems definitely worth it.