Re: Correct the documentation for work_mem

On Fri, Apr 21, 2023 at 01:15:01PM -0400, Tom Lane wrote:
> Peter Eisentraut <peter.eisentraut@enterprisedb.com> writes:
> > On 21.04.23 16:28, Imseih (AWS), Sami wrote:
> >> I suggest a small doc fix:
> >> “Note that for a complex query, several sort or hash operations might be 
> >> running simultaneously;”
> 
> > Here is a discussion of these terms: 
> > https://takuti.me/note/parallel-vs-concurrent/
> 
> > I think "concurrently" is the correct word here.
> 
> Probably, but it'd do little to remove the confusion Sami is on about,
> especially since the next sentence uses "concurrently" to describe the
> other case.  I think we need a more thorough rewording, perhaps like
> 
> -       Note that for a complex query, several sort or hash operations might be
> -       running in parallel; each operation will generally be allowed
> +       Note that a complex query may include several sort or hash
> +       operations; each such operation will generally be allowed
>         to use as much memory as this value specifies before it starts
>         to write data into temporary files.  Also, several running
>         sessions could be doing such operations concurrently.
> 
> I also find this wording a bit further down to be poor:
> 
>         Hash-based operations are generally more sensitive to memory
>         availability than equivalent sort-based operations.  The
>         memory available for hash tables is computed by multiplying
>         <varname>work_mem</varname> by
>         <varname>hash_mem_multiplier</varname>.  This makes it
> 
> I think "available" is not le mot juste, and it's also unclear from
> this whether we're speaking of the per-hash-table limit or some
> (nonexistent) overall limit.  How about
> 
> -       memory available for hash tables is computed by multiplying
> +       memory limit for a hash table is computed by multiplying

Adjusted patch attached.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

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