Re: TSearch2: find a QUERY that does match a single document

["Dmitry Koterov" <dmitry@xxxxxxxxxx>]

explain analyze
select * from test.test_tsq
where to_tsvector('400000x400000') @@ q

why do you need tsvector @@ q ? Much better to use  tsquery = tsquery

test=# explain analyze select * from test_tsq where q = '400000x400000'::tsque>
                                               QUERY PLAN
-----------------------------------------------------------------------------------------------------------
 Seq Scan on test_tsq  (cost=0.00..16667.01 rows=1 width=38) (actual time=129.208..341.111 rows=1 loops=1)
  Filter: (q = '''400000x400000'''::tsquery)
 Total runtime: 341.134 ms
(3 rows)

M-mmm... Seems your understood me incorrectly.

I have to find NOT queries which are exactly equal to another query, BUT queries which MATCH the GIVEN document. '400000x400000' was a sample only, in real cases it will be 1-2K document.

Here is a more realistic sample:

explain analyze
select * from test.test_tsq
where to_tsvector('
  Here is a real document text. It may be long, 1-2K.
  In this sample it contains a lexem "400000x400000", so there is a tsquery
  in test_tsq.q which matches this document. I need to find all such queries fast.
  Of course, in real cases the document text is unpredictable.
') @@ q

 

QUERY PLAN
Seq Scan on test_tsq  (cost=0.00..17477.01 rows=800 width=36) (actual
time=68.698..181.458 rows=1 loops=1)
 Filter: ('''400000x400000'':1'::tsvector @@ q)
Total runtime: 181.484 ms

'800' is the number of estimated rows, which is not good, since you got only 1 row.

Why 800? The table contains 800000 rows, and seqscan is used. Does it scan the whole table or not? If yes, possibly there is a bug in explain output? (No mater if I create GIST index on test_tsq.q or not, the number of rows is still 800, so it seems to me that GIST index is not used at all.)