Date: Mon, 18 Feb 2019 10:49:56 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Bruce Momjian <bruce@momjian.us>, Andres Freund <andres@anarazel.de>,
	Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>,
	tsunakawa.takay@jp.fujitsu.com, robertmhaas@gmail.com,
	tgl@sss.pgh.pa.us, ideriha.takeshi@jp.fujitsu.com,
	pgsql-hackers@lists.postgresql.org, michael.paquier@gmail.com,
	david@pgmasters.net, craig@2ndquadrant.com
Subject: Re: Protect syscache from bloating with negative cache entries
Message-ID: <20190218134956.GA909@alvherre.pgsql>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <b79b09bd-fa8f-8501-0781-fa4e3619bd54@2ndquadrant.com>
User-Agent: Mutt/1.9.4 (2018-02-28)
Precedence: bulk

On 2019-Feb-15, Tomas Vondra wrote:

> ISTM there's a couple of ways to deal with that:
> 
> 1) Ignore the memory amounts entirely, and do just time-base eviction.
> 
> 2) If we want some size thresholds (e.g. to disable eviction for
> backends with small caches etc.) use the number of entries instead. I
> don't think that's particularly worse that specifying size in MB.

Why is there a *need* for size-based eviction?  Seems that time-based
should be sufficient.  Is the proposed approach to avoid eviction at all
until the size threshold has been reached?  I'm not sure I see the point
of that.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services