Hi,
Short: postrgesql-7.2.3 doesn't figure to convert int4 to int8
implicitly / by context (as in a query). How do I help it ?
Long: I have index on a table, a select like this takes a split second:
# select * from file where id = fileIDseq.last_value-1; id | name -----+----------------
1921777 | icons
but a select like this takes ages (looooong time):
# select * from file where id = 1921773; id | name -----+----------------
1921777 | icons
but a select like this is quick again:
# select * from file where id = int8(1921773); id | name -----+----------------
1921777 | icons
the secret seems to be that
# explain select * from file where id = fileIDseq.last_value-1;
Nested Loop (cost=0.00..6.04 rows=1 width=1359) -> Seq Scan on fileidseq (cost=0.00..1.01 rows=1 width=8) -> Index
Scanusing file_pkey on file (cost=0.00..5.02 rows=1 width=1351)
whereas
# explain select * from file where id = 1921773;
Seq Scan on file (cost=0.00..58905.95 rows=1 width=1351)
The reason seems to be that fileIDseq.last_value-1 is type bigint(int8), whereas "1921773" is of type integer (int4).
Now
# explain select * from file where id in (fileIDseq.last_value-1,fileIDseq.last_value-1);
Nested Loop (cost=0.00..6.04 rows=1 width=1359) -> Seq Scan on fileidseq (cost=0.00..1.01 rows=1 width=8) -> Index
Scanusing file_pkey on file (cost=0.00..5.02 rows=1 width=1351)BUT
# explain select * from file where id in (fileIDseq.last_value-1,fileIDseq.last_value-333); -- "-333" instead of same
"-1"
Nested Loop (cost=0.00..92278.69 rows=2 width=1359) -> Seq Scan on fileidseq (cost=0.00..1.01 rows=1 width=8) ->
SeqScan on file (cost=0.00..54138.56 rows=1906956 width=1351)
Why ?
Also, how do I tell postgresql that it should by default interpret
integers as "int8"s, and not as "int4"s ? (So that I don't have to
keep saying "int8(XYZ)" as in "select * from file where id = int8(1);"
Thanks,
John
mydb# \d file Table "file" Column | Type |
Modifiers
----------+-----------------------------+---------------------------------------------id | bigint
| not null default nextval('fileIDseq'::text)name | character varying(255) |
Primary key: file_pkey
mydb=# \d file_pkey
Index "file_pkey"Column | Type
--------+--------id | bigint
unique btree (primary key)
mydb==# \d fileidseq Sequence "fileidseq" Column | Type
---------------+---------sequence_name | namelast_value | bigintincrement_by | bigintmax_value |
bigintmin_value | bigintcache_value | bigintlog_cnt | bigintis_cycled | booleanis_called | boolean
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