Re: Compressed TOAST Slicing

Greetings,

* Paul Ramsey (pramsey(at)cleverelephant(dot)ca) wrote:
> On Wed, Feb 20, 2019 at 10:50 AM Daniel Verite <daniel(at)manitou-mail(dot)org> wrote:
> >
> > Paul Ramsey wrote:
> >
> > > Oddly enough, I couldn't find many/any things that were sensitive to
> > > left-end decompression. The only exception is "LIKE this%" which
> > > clearly would be helped, but unfortunately wouldn't be a quick
> > > drop-in, but a rather major reorganization of the regex handling.
> >
> > What about starts_with(string, prefix)?
> >
> > text_starts_with(arg1,arg2) in varlena.c does a full decompression
> > of arg1 when it could limit itself to the length of the smaller arg2:
>
> Nice catch, I didn't find that one as it's not user visible, seems to
> be only called in spgist (!!)
> ./backend/access/spgist/spgtextproc.c:
> DatumGetBool(DirectFunctionCall2(text_starts_with
>
> Thanks, I'll add that.

That sounds good to me, I look forward to an updated patch. As Andres
mentioned, he and I chatted a bit about this approach vs the iterator
approach at FOSDEM and convinced me that this is worthwhile to do even
if we might add an iterator approach later- which also seems to be the
consensus of this thread, so once the patch has been updated to catch
this case, I'll review it (again) with an eye on committing it soon.

Thanks!

Stephen