On Fri, Oct 10, 2014 at 9:53 AM, Tomas Vondra <tv@xxxxxxxx> wrote:
On 10.10.2014 16:21, Craig James wrote:
> Our index is for chemical structures. Chemicals are indexed on
> chemical fragments
> <http://emolecules.com/info/molecular-informatics>. A search
> typically starts with 50-200 indexed "columns" (chemical fragments).
> The query is always flat, "A and B and ... and Z". The indexed
> fragments are both correlated (the existence of one strongly raises
> the chances of another) and anti-correlated (certain combinations are
> very rare).
Maybe I don't understand the problem well enough, but isn't this a
perfect match for GIN indexes? I mean, you essentially need to do
queries like "WHERE substance @@ ('A & B & !C')" etc. Which is exactly
what GIN does, because it keeps pointers to tuples for each fragment.
On the day our web site opened we were using tsearch. Before the end of the day we realized it was a bad idea, for the very reasons discussed here. The early-abort/late-start problem ("offset N limit M") could take minutes to return the requested page. With the external dynamically-optimized index, we can almost always get answers in less than a couple seconds, often in 0.1 seconds.
Craig
