Using bigint needs explicit cast to use the index
От | Steven Butler |
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Тема | Using bigint needs explicit cast to use the index |
Дата | |
Msg-id | 001101c404a3$fb34d320$fd08a8c0@steve обсуждение исходный текст |
Ответы |
Re: Using bigint needs explicit cast to use the index
Re: Using bigint needs explicit cast to use the index |
Список | pgsql-performance |
Hi, I've recently converted a database to use bigint for the indices. Suddenly simple queries like select * from new_test_result where parent_id = 2 are doing full table scans instead of using the index. The table has over 4 million rows, of which only 30 or so would be selected by the query. The database table in question was fully vacuumed and clustered on the index. I tried disabling seqscan, but it still did full table scan. After browsing around a bit, I had a hunch it might be failing to use the index because it is perhaps converting the parent_id to an integer, and I don't have a functional index on that (wouldn't seem correct either). I tested my hunch by casting the constant to bigint (as can be seen below) and suddenly the query is using the index again. We are currently using pg 7.3.4. Is this intended behaviour? Should the constant be cast to the type of the table column where possible, or should it be the other way around? If this is considered a bug, is it already fixed, in 7.3.6 or 7.4.x? Kind Regards, Steve Butler steve=# \d new_test_result; Table "public.new_test_result" Column | Type | Modifiers -----------+---------+------------------------------------------------------ ----------- id | bigint | not null default nextval('public.new_test_result_id_seq'::text) parent_id | bigint | testcode | text | testtype | text | testdesc | text | pass | integer | latency | integer | bytessent | integer | bytesrecv | integer | defect | text | Indexes: test_result_parent_id_fk btree (parent_id) Foreign Key constraints: $1 FOREIGN KEY (parent_id) REFERENCES new_test_run(id) ON UPDATE NO ACTION ON DELETE CASCADE steve=# explain select * from new_test_result where parent_id = 2; QUERY PLAN ----------------------------------------------------------------------- Seq Scan on new_test_result (cost=0.00..123370.57 rows=23 width=125) Filter: (parent_id = 2) (2 rows) steve=# explain select * from new_test_result where parent_id = 2::bigint; QUERY PLAN ---------------------------------------------------------------------------- ----------------------- Index Scan using test_result_parent_id_fk on new_test_result (cost=0.00..3.32 rows=23 width=125) Index Cond: (parent_id = 2::bigint) (2 rows)
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