Re: Binary search in fmgr_isbuiltin() is a bottleneck.

Hi Andres,

Another idea would be to have an array of FmgrBuiltin*, that we index by
> oid. That'd not be super small though, given that the space for function
> oids is sparse.
>
>
I totally agree here, as the oids are very much scattered having an
array is not feasible here.

> Thus what I've instead done is replacing the binary search in
> fmgr_isbuiltin() with a simplehash.h style hashtable. After that the
> lookup is still visible in the profile, but far less prominent.
>
> I'd like to move the hash creation out of fmgr_isbuiltin (to avoid
> having to check whether it's already created), but there's currently no
> convenient place to create the hash from. Now that we don't rely on
> the sortedness of fmgrtab.c we could remove a few lines from
> Gen_fmgrtab.pl, but I don't quite see the advantage. If we were
> interested in a faster by-name lookup we could sort it by name, but
> that'd be better solved by another hashtable...
>

I looked into these patches.
Seems patch 004 is already committed, commit id:
791961f59b792fbd4f0a992d3ccab47298e79103

About patch 0005:
The patch still applies cleanly.
There are no failures in ‘make check’

+ /* TODO: it'd be better if this were done separately */
+ if (unlikely(oid2builtins == NULL))
{
- int i = (high + low) / 2;
- const FmgrBuiltin *ptr = &fmgr_builtins[i];
+ int i;

- if (id == ptr->foid)
- return ptr;
- else if (id > ptr->foid)
- low = i + 1;
- else
- high = i - 1;
+ oid2builtins = oid2builtins_create(TopMemoryContext,
+ fmgr_nbuiltins,
+ NULL);
+ for (i = 0; i < fmgr_nbuiltins; i++)
+ {
+ const FmgrBuiltin *ptr = &fmgr_builtins[i];
+ bool found;
+
+ entry = oid2builtins_insert(oid2builtins, ptr->foid, &found);
+ Assert(!found);
+ entry->builtin = ptr;
+ }

As Andres has already pointed, may be we want to move above code in a
separate
function, and just call that function here in case the hash is not already
built.

Further I am thinking about doing some performance testing, Andres can you
please
point me how did you test it and what perf numbers you saw for this
particular patch(0005).

Regards,
Jeevan Ladhe