Re: query performance

Sorry Alex i forget mention that i have setscan of in my last test.

now I have set seqscan on and indexscan on and added order by _id

The table has an index in the _id field

CREATE INDEX i_documentcontent_document
ON t_documentcontent
USING btree
(_document);

The database was rencently vacum analyze , but not vacun full

here is the explain of 2 diferent queries , when i put a large OFFSET

EXPLAIN ANALYZE SELECT
t_documentcontent._id AS _id
FROM t_documentcontent ORDER BY _id LIMIT 50 OFFSET 50000

"Limit (cost=137068.24..137068.36 rows=50 width=58) (actual time=
41119.702..41119.792 rows=50 loops=1)"
" -> Sort (cost=136943.24..137320.26 rows=150807 width=58) (actual time=
41064.802..41100.424 rows=50050 loops=1)"
" Sort Key: _id"
" -> Seq Scan on t_documentcontent (cost=
0.00..110772.07rows=150807 width=58) (actual time=
106.679..33267.194 rows=150807 loops=1)"
"Total runtime: 41120.015 ms"

EXPLAIN ANALYZE SELECT
t_documentcontent._id AS _id
FROM t_documentcontent ORDER BY _id LIMIT 50 OFFSET 10000

"Limit (cost=39839.37..40038.56 rows=50 width=58) (actual time=
1172.969..1194.228 rows=50 loops=1)"
" -> Index Scan using i_documentcontent_id on t_documentcontent (cost=
0.00..600805.54 rows=150807 width=58) (actual time=
0.077..1189.688rows=10050 loops=1)"
"Total runtime: 1194.316 ms"

Tom
i using uuid for the _id field that is the primary key add a WHERE id > ?
don 't apply
the cursor aproach is also not suitable for same of my queries

I use this query for paginate contents of a filesysstem with lots of
documents avoid offset is not posible always