Re: Searching GIN-index (FTS) and sort by timestamp-column - Mailing list pgsql-performance
På onsdag 16. mars 2016 kl. 16:07:56, skrev Evgeniy Shishkin <itparanoia@gmail.com>:
> On 16 Mar 2016, at 18:04, Evgeniy Shishkin <itparanoia@gmail.com> wrote:
>
>>
>> On 16 Mar 2016, at 17:52, Evgeniy Shishkin <itparanoia@gmail.com> wrote:
>>
>>
>>> On 16 Mar 2016, at 16:37, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>>
>>> Andreas Joseph Krogh <andreas@visena.com> writes:
>>>> 1. Why isnt' folder_id part of the index-cond?
>>>
>>> Because a GIN index is useless for sorting.
>>
>> I don't see how gin inability to return sorted data relates to index condition.
>> In fact i tried to reproduce the example,
>> and if i change folder_id to int from bigint, then index condition with folder_id is used
>>
>> Index Cond: ((fts_all @@ '''hi'''::tsquery) AND (folder_id = 1))
>>
>
> Looks like documentation http://www.postgresql.org/docs/9.5/static/btree-gin.html
> is lying about supporting int8 type
>
Uh, it works if i cast to bigint explicitly
WHERE del.fts_all @@ to_tsquery('simple', 'hi')
AND del.folder_id = 1::bigint;
results in
Index Cond: ((folder_id = '1'::bigint) AND (fts_all @@ '''hi'''::tsquery))
Hm, this is quite cranky, but thanks for the heads-up!
Tho it looks like it works if prepared, without explicit cast:
prepare fish AS
SELECT del.id , del.received_timestamp FROM delivery del WHERE 1 = 1
AND del.fts_all @@ to_tsquery('simple', $1) AND del.folder_id = $2 ORDER BY del.received_timestamp DESC LIMIT 101 OFFSET 0;
explain analyze execute fish('hi:*', 1);
QUERY PLAN
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
Limit (cost=9.13..9.13 rows=1 width=16) (actual time=0.047..0.048 rows=2 loops=1)
-> Sort (cost=9.13..9.13 rows=1 width=16) (actual time=0.045..0.045 rows=2 loops=1)
Sort Key: received_timestamp DESC
Sort Method: quicksort Memory: 25kB
-> Bitmap Heap Scan on delivery del (cost=7.80..9.12 rows=1 width=16) (actual time=0.034..0.034 rows=2 loops=1)
Recheck Cond: ((fts_all @@ '''hi'':*'::tsquery) AND (folder_id = '1'::bigint))
Heap Blocks: exact=1
-> Bitmap Index Scan on fts_idx (cost=0.00..7.80 rows=1 width=0) (actual time=0.023..0.023 rows=2 loops=1)
Index Cond: ((fts_all @@ '''hi'':*'::tsquery) AND (folder_id = '1'::bigint))
Execution time: 0.103 ms
(10 rows)
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
Limit (cost=9.13..9.13 rows=1 width=16) (actual time=0.047..0.048 rows=2 loops=1)
-> Sort (cost=9.13..9.13 rows=1 width=16) (actual time=0.045..0.045 rows=2 loops=1)
Sort Key: received_timestamp DESC
Sort Method: quicksort Memory: 25kB
-> Bitmap Heap Scan on delivery del (cost=7.80..9.12 rows=1 width=16) (actual time=0.034..0.034 rows=2 loops=1)
Recheck Cond: ((fts_all @@ '''hi'':*'::tsquery) AND (folder_id = '1'::bigint))
Heap Blocks: exact=1
-> Bitmap Index Scan on fts_idx (cost=0.00..7.80 rows=1 width=0) (actual time=0.023..0.023 rows=2 loops=1)
Index Cond: ((fts_all @@ '''hi'':*'::tsquery) AND (folder_id = '1'::bigint))
Execution time: 0.103 ms
(10 rows)
-- 
Andreas Joseph Krogh
CTO / Partner - Visena AS
Mobile: +47 909 56 963
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