Date: Mon, 5 Nov 2018 11:12:31 -0500
From: Bruce Momjian <bruce@momjian.us>
To: Nikolay Samokhvalov <samokhvalov@gmail.com>
Cc: peter.eisentraut@2ndquadrant.com, nat@makarevitch.org,
	pgsql-docs@lists.postgresql.org
Subject: Re: effective_cache_size
Message-ID: <20181105161231.GA13780@momjian.us>
References: <153685164808.22334.15432535018443165207@wrigleys.postgresql.org>
 <20181011174849.GC7807@momjian.us>
 <20181016153820.GD31154@momjian.us>
 <369ec766-b947-51bd-4dad-6fb9e026439f@2ndquadrant.com>
 <20181105120104.GA13769@momjian.us>
 <CANNMO++QsKXLm1E=8uSnSJYgLC5ZJnAYxJZogTLfYdGUXrcV3g@mail.gmail.com>
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On Mon, Nov  5, 2018 at 03:23:03PM +0300, Nikolay Samokhvalov wrote:
> 
> 
> On Mon, Nov 5, 2018 at 3:01 PM Bruce Momjian <bruce@momjian.us> wrote:
> 
>     > >             {"effective_cache_size", PGC_USERSET, QUERY_TUNING_COST,
>     > > -                   gettext_noop("Sets the planner's assumption about
>     the size of the disk cache."),
>     > > -                   gettext_noop("That is, the portion of the kernel's
>     disk cache that "
>     > > -                                            "will be used for
>     PostgreSQL data files. This is measured in disk "
>     > > -                                            "pages, which are normally
>     8 kB each."),
>     > > +                   gettext_noop("Sets the planner's assumption about
>     the size of the data cache."),
>     > > +                   gettext_noop("That is, the size of the cache used
>     for PostgreSQL data files. "
>     > > +                                            "This is measured in disk
>     pages, which are normally 8 kB each."),
> 
> ...
> 
>     Well, the change as outlined in the email is that effective_cache_size
>     is a combination of shared_buffers and kernel cache size, which I think
>     the docs now make clear.  Do you have better wording for the GUC?
> 
> 
> Maybe it's better to use this phrase, "a combination of shared_buffers and
> kernel cache size"?
> Or: "a combination of shared_buffers and estimated kernel cache size".

Well, here are the lines in guc.c:

            gettext_noop("Sets the planner's assumption about the size of the data cache."),
            gettext_noop("That is, the size of the cache used for PostgreSQL data files. "
                         "This is measured in disk pages, which are normally 8 kB each."),

The first line is already on the long side compared to other entries, as
is the second gettext_noop().  How long can we make it without being too
long?  Is this really the place to explain this distinction?  I thought
about these issues when I wrote this patch?  You can come to a different
conclusion, but please consider these issues.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +