Re: effective_cache_size

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(at)momjian(dot)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(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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