Re: Trigram is slow when 10m rows

On Sun, Nov 13, 2016 at 2:54 PM, Aaron Lewis <the(dot)warl0ck(dot)1989(at)gmail(dot)com>
wrote:

> I have a simple table with Trigram index,
>
> create table mytable(hash char(40), title text);
> create index title_trgm_idx on mytable using gin(title gin_trgm_ops);
>
> When I run a query with 10m rows, it uses the Trigram index, but takes
> 3s to execute, very slow.
> (I have 80m rows, but only inserted 10m for testing purpose)
>
> test=# select count(*) from mytable;
> count
> ----------
> 13971887
> (1 row)
>
> test=# explain analyze select * from mytable where title ilike 'x264';
> QUERY PLAN
> ------------------------------------------------------------
> --------------------------------------------------------------------------
> Bitmap Heap Scan on mytable (cost=462.69..5639.67 rows=1380
> width=83) (actual time=2937.308..2937.308 rows=0 loops=1)
> Recheck Cond: (title ~~* 'x264'::text)
> Rows Removed by Index Recheck: 11402855
> Heap Blocks: exact=39557 lossy=158010
> -> Bitmap Index Scan on title_trgm_idx (cost=0.00..462.35
> rows=1380 width=0) (actual time=342.440..342.440 rows=1220793 loops=1)
> Index Cond: (title ~~* 'x264'::text)
> Planning time: 0.611 ms
> Execution time: 2937.729 ms
> (8 rows)
>
> Any ideas to speed things up?
>

Rows Removed by Index Recheck: 11402855
Heap Blocks: exact=39557 lossy=158010

You need to increase work_mem

>
> --
> Best Regards,
> Aaron Lewis - PGP: 0x13714D33 - http://pgp.mit.edu/
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