> > {"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".
The phrase "the size of the cache" might be very confusing indeed – it sounds like it's about
some single cache, while it's about the combination of two.
Maybe it's also worth to mention that the fact that some pages might be cached twice –
in OS cache + in Postgres shared buffers – should be ignored, when choosing the proper value
for effective_cache_size? I think this would finally eliminate the possibility of confusion.
I see now, the docs chapter "19.7. Query Planning" has "some data might exist in both places"
– this is great, since confusion here is not uncommon. It's worth to propagate this change
everywhere where effective_cache_size is explained.
Nik