Hackes,
attached patch implementing "fast scan" technique for GIN. This is second patch of GIN improvements, see the 1st one here:
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)
------
With best regards,
Alexander Korotkov.
