Hi, hackers:
I am testing the index used by full text search recently.
I have install 8.3.9 and 8.4.2 separately.
In 8.3.9, the query plan is like:
postgres=# explain SELECT s.name as source , t.name as target FROM element as
s, element as t WHERE to_tsvector('testcfg',s.name) @@
to_tsquery('testcfg',replace(t.name,':','|'));
QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------------------------------
Nested Loop (cost=0.01..259.92 rows=491 width=18)
-> Seq Scan on element t (cost=0.00..13.01 rows=701 width=9)
-> Index Scan using element_ftsidx_test on element s (cost=0.01..0.33 rows=1
width=9)
Index Cond: (to_tsvector('testcfg'::regconfig, (s.name)::text) @@
to_tsquery('testcfg'::regconfig, replace((t.name)::text, ':'::text, '|'::text)))
(4 rows)
I have index: "element_ftsidx_test" gin (to_tsvector('testcfg'::regconfig,
name::text))
The same index and query in 8.4.2:
postgres=# explain SELECT s.name as source , t.name as target FROM element as
s, element as t WHERE to_tsvector('testcfg',s.name) @@
to_tsquery('testcfg',replace(t.name,':','|')) ;
QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Nested Loop (cost=0.32..3123.51 rows=2457 width=18)
-> Seq Scan on element t (cost=0.00..13.01 rows=701 width=9)
-> Bitmap Heap Scan on element s (cost=0.32..4.36 rows=4 width=9)
Recheck Cond: (to_tsvector('testcfg'::regconfig, (s.name)::text) @@
to_tsquery('testcfg'::regconfig, replace((t.name)::text, ':'::text,
'|'::text)))
-> Bitmap Index Scan on element_ftsidx_test (cost=0.00..0.32 rows=4
width=0)
Index Cond: (to_tsvector('testcfg'::regconfig, (s.name)::text) @@
to_tsquery('testcfg'::regconfig, replace((t.name)::text, ':'::text, '|'::text)))
(6 rows)
Why the query plans are different and why? Thanks!
Xu Fei
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