postgresql - What's wrong with GIN index, can't avoid SEQ scan? -

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i've created table this,

create table mytable(hash char(40), title varchar(500)); create index name_fts on mytable using gin(to_tsvector('english', 'title')); create unique index md5_uniq_idx on mytable(hash);

when query title,

test=# explain analyze select * mytable to_tsvector('english', title) @@ 'abc | def'::tsquery limit 10;                                                      query plan --------------------------------------------------------------------------------------------------------------------  limit  (cost=0.00..277.35 rows=10 width=83) (actual time=0.111..75.549 rows=10 loops=1)    ->  seq scan on mytable  (cost=0.00..381187.45 rows=13744 width=83) (actual time=0.110..75.546 rows=10 loops=1)          filter: (to_tsvector('english'::regconfig, (title)::text) @@ '''abc'' | ''def'''::tsquery)          rows removed filter: 10221  planning time: 0.176 ms  execution time: 75.564 ms (6 rows)

the index not used. ideas? have 10m rows.

there typo in index definition, should be

on mytable using gin (to_tsvector('english', title))

instead of

on mytable using gin (to_tsvector('english', 'title'))

the way wrote it, constant , not field indexed, , such index indeed useless search 1 perform.

to see if index can used, can execute

set enable_seqscan=off;

and run query again.
if index still not used, index cannot used.

in addition above, there strikes me strange execution plan. postgresql estimates sequential scan of mytable return 13744 rows , not 10 million there are. did disable autovacuum or there else cause table statistics inaccurate?


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