On Sat, Jun 15, 2013 at 2:55 AM, Alexander Korotkov <aekorot...@gmail.com>wrote:
> attached patch implementing "fast scan" technique for GIN. This is second > patch of GIN improvements, see the 1st one here: > > http://www.postgresql.org/message-id/capphfduxv-il7aedwpw0w5fxrwgakfxijwm63_hzujacrxn...@mail.gmail.com > This patch allow to skip parts of posting trees when their scan is not > necessary. In particular, it solves "frequent_term & rare_term" problem of > FTS. > It introduces new interface method pre_consistent which behaves like > consistent, but: > 1) allows false positives on input (check[]) > 2) allowed to return false positives > > Some example: "frequent_term & rare_term" becomes pretty fast. > > create table test as (select to_tsvector('english', 'bbb') as v from > generate_series(1,1000000)); > insert into test (select to_tsvector('english', 'ddd') from > generate_series(1,10)); > create index test_idx on test using gin (v); > > postgres=# explain analyze select * from test where v @@ > to_tsquery('english', 'bbb & ddd'); > QUERY PLAN > > ----------------------------------------------------------------------------------------------------------------------- > Bitmap Heap Scan on test (cost=942.75..7280.63 rows=5000 width=17) > (actual time=0.458..0.461 rows=10 loops=1) > Recheck Cond: (v @@ '''bbb'' & ''ddd'''::tsquery) > -> Bitmap Index Scan on test_idx (cost=0.00..941.50 rows=5000 > width=0) (actual time=0.449..0.449 rows=10 loops=1) > Index Cond: (v @@ '''bbb'' & ''ddd'''::tsquery) > Total runtime: 0.516 ms > (5 rows) > Attached version of patch has some refactoring and bug fixes. ------ With best regards, Alexander Korotkov.
gin_fast_scan.2.patch.gz
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