Re: [GENERAL] Creation of tsearch2 index is very slow - Mailing list pgsql-performance

From Steinar H. Gunderson
Subject Re: [GENERAL] Creation of tsearch2 index is very slow
Date
Msg-id 20060120225751.GA27230@uio.no
Whole thread Raw
In response to Re: [GENERAL] Creation of tsearch2 index is very slow  (Tom Lane)
Responses Re: [GENERAL] Creation of tsearch2 index is very slow  (Tom Lane)
List pgsql-performance
On Fri, Jan 20, 2006 at 05:50:36PM -0500, Tom Lane wrote:
> Yeah, but fetching from a small constant table is pretty quick too;
> I doubt it's worth getting involved in machine-specific assembly code
> for this.  I'm much more interested in the idea of improving the
> furthest-distance algorithm in gtsvector_picksplit --- if we can do
> that, it'll probably drop the distance calculation down to the point
> where it's not really worth the trouble to assembly-code it.

For the record: Could we do with a less-than-optimal split here? In that
case, an extremely simple heuristic is:

  best = distance(0, 1)
  best_i = 0
  best_j = 1

  for i = 2..last:
      if distance(best_i, i) > best:
          best = distance(best_i, i)
      best_j = i
      else if distance(best_j, i) > best:
          best = distance(best_j, i)
      best_i = i

I've tested it on various data, and although it's definitely not _correct_,
it generally gets within 10%.

/* Steinar */
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