On 14/12/13 12:54, Andres Freund wrote:
On 2013-12-14 13:59:02 +0400, Alexander Korotkov wrote:
Currently when we need to get ordered result from table we have to choose
one of two approaches: get results from index in exact order we need or do
sort of tuples. However, it could be useful to mix both methods: get
results from index in order which partially meets our requirements and do
rest of work from heap.
------------------------------------------------------------------------------------------------------------------------------------------
Limit (cost=69214.06..69214.08 rows=10 width=16) (actual
time=0.097..0.099 rows=10 loops=1)
-> Sort (cost=69214.06..71714.06 rows=1000000 width=16) (actual
time=0.096..0.097 rows=10 loops=1)
Sort Key: v1, v2
Sort Method: top-N heapsort Memory: 25kB
-> Index Scan using test_v1_idx on test (cost=0.42..47604.42
rows=1000000 width=16) (actual time=0.017..0.066 rows=56 loops=1)
Total runtime: 0.125 ms
(6 rows)
Is that actually all that beneficial when sorting with a bog standard
qsort() since that doesn't generally benefit from data being pre-sorted?
I think we might need to switch to a different algorithm to really
benefit from mostly pre-sorted input.
Eg: http://www.postgresql.org/message-id/5291467e.6070...@wizmail.org
Maybe Alexander and I should bash our heads together.
--
Cheers,
Jeremy
--
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers
