Hi I developed a new character string type, named myvarchar. Also an operator class for btree is added.
I created a table with two columns, first have myvarchar(100) and other is varchar(100). CREATE TABLE test_myvarchar (mine myvarchar(100), plain varchar(100)); CREATE INDEX test_myvarchar_i_mine ON test_myvarchar USING btree (mine); CREATE INDEX test_myvarchar_i_plain ON test_myvarchar USING btree (plain); Two same random strings to both of columns are inserted, and the operation repeated until 32K rows are in the table. INSERT INTO test_myvarchar VALUES ('example', 'example'); PROBLEM: When I executed a query with where clause on 'mine' column, PG does not use index. But after I changed where clause to be on 'plain' column, PG uses index! EXPLAIN SELECT * FROM test_myvarchar WHERE 'zagftha' >= mine ORDER BY 1; ---------------------- Sort (cost=3038.39..3065.00 rows=10642 width=197) Sort Key: mine -> Seq Scan on test_myvarchar (cost=0.00..1308.08 rows=10642 width=197) Filter: ('zagftha'::myvarchar >= mine) ############################################## EXPLAIN SELECT * FROM test_myvarchar WHERE 'zagftha' >= plain ORDER BY 2; Index Scan using test_myvarchar_i_plain on test_myvarchar (cost=0.41..6099.0 8 rows=31175 width=197) Index Cond: ('zagftha'::text >= (plain)::text) Why planner does not choose the lowest cost path? Is there any problem with my new type? How can I fix it? Any help would be appreciated. Regards, Soroosh Sardari Sharif University of Technology