Hi,
Hope someone can spot where I'm going wrong here.
I'm transferring a database & reporting scripts across from Oracle & a few
of the SQL statements behave a little differently with regards to indexes.
The one that's got me stumped at the moment is this...
select * from messages, statusinds
WHERE statusinds.gateway_id = messages.gateway_id
AND (messages.client_id = '7' AND messages.user_name in ('U66515'))
limit 5;
It's using the index on the messages table. On Oracle, it would do a
sequential index scan on the messages table & lookup the appropriate entry
in the statusinds table using the index. However, on Postgres, I can't get
it to use the statusinds index - it does a sequential scan through the
entire table each time! As you can imagine, it's taking ages to do this
where it used to take a few seconds on Oracle.
I've tried explicitly specifying the JOIN type & I can't seem to find the
right combination. I've tried doing a simple select on statusinds where
gateway_id = 'xxx' and the explain tells me it's doing index lookups.
Indexes are as follows...
-- Index: statusinds_200204_ix1
CREATE UNIQUE INDEX statusinds_ix1 ON statusinds USING btree (gateway_id,
status, logtime);
-- Index: messages_200204_ix1
CREATE UNIQUE INDEX messages_200204_ix1 ON messages_200204 USING btree
(host, qos_id);
Explain plan....
Limit (cost=0.00..35.06 rows=5 width=620)
-> Nested Loop (cost=0.00..30986063.51 rows=4418898 width=620)
-> Append (cost=0.00..441.93 rows=111 width=496)
-> Seq Scan on messages (cost=0.00..0.00 rows=1 width=496)
-> Index Scan using messages_200203_ix2 on messages_200203 messages
(cost=0.00..272.61 rows=68 width=383)
-> Index Scan using messages_200204_ix2 on messages_200204 messages
(cost=0.00..169.32 rows=42 width=384)
-> Append (cost=0.00..180413.11 rows=7996912 width=124)
-> Seq Scan on statusinds (cost=0.00..0.00 rows=1 width=124)
-> Seq Scan on statusinds_200203 statusinds (cost=0.00..142835.73
rows=6292073 width=71)
-> Seq Scan on statusinds_200204 statusinds (cost=0.00..37577.38
rows=1704838 width=65)
(tables_YYYYMM are inherited)
--
Ian Cass
