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

On 2017-10-02 17:57:51 -0400, Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
> > Done that way. It's a bit annoying, because we've to take care to
> > initialize the "unused" part of the array with a valid signalling it's
> > an unused mapping. Can't use 0 for that because fmgr_builtins[0] is a
> > valid entry.
> 
> The prototype code I posted further upthread just used -1 as the "unused"
> marker. There's no reason the array can't be int16 rather than uint16,
> and "if (index < 0)" is probably a faster test anyway.

Right, but whether we use -1 or UINT16_MAX or such doesn't matter. The
relevant bit is that we can't use 0, so we can't rely on the rest of the
array being zero initialized, but instead of to initialize all of it
explicitly.  I've no real feelings about using -1 or UINT16_MAX - I'd be
very surprised if there's any sort of meaningful performance difference.

Greetings,

Andres Freund