From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Michael Lewis <mlewis(at)entrata(dot)com> |
Cc: | Ninad Shah <nshah(dot)postgres(at)gmail(dot)com>, balasubramanian c r <crbs(dot)siebel(at)gmail(dot)com>, pgsql-general <pgsql-general(at)lists(dot)postgresql(dot)org> |
Subject: | Re: Querying a table with jaccard similarity with 1.6 million records take 12 seconds |
Date: | 2021-09-02 19:44:09 |
Message-ID: | 2266571.1630611849@sss.pgh.pa.us |
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Lists: | pgsql-general |
Michael Lewis <mlewis(at)entrata(dot)com> writes:
> This is showing many false positives from the index scan that get removed
> when the actual values are examined. With such a long search parameter,
> that does not seem surprising. I would expect a search on "raj nagar
> ghaziabad 201017" or something like that to yield far fewer results from
> the index scan. I don't know GIN indexes super well, but I would guess that
> including words that are very common will yield false positives that get
> filtered out later.
Yeah, the huge "Rows Removed" number shows that this index is very
poorly adapted to the query. I don't think the problem is with GIN
per se, but with a poor choice of how to use it. The given example
looks like what the OP really wants to do is full text search.
If so, a GIN index should be fine as long as you put tsvector/tsquery
filtering in front of it. If that's not a good characterization of
the goal, it'd help to tell us what the goal is. (Just saying "I
want to use jaccard similarity" sounds a lot like a man whose only
tool is a hammer, therefore his problem must be a nail, despite
evidence to the contrary.)
regards, tom lane
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