Hi,
I have a table that looks like this:
DATA ID TIME
|------|----|------|
The table holds app. 14M rows now and grows by app. 350k rows a day.
The ID-column holds about 1500 unique values (integer).
The TIME-columns is of type timestamp without timezone.
I have one index (b-tree) on the ID-column and one index (b-tree) on the
time-column.
My queries most often look like this:
SELECT DATA FROM <tbl> WHERE ID = 1 AND TIME > now() - '1 day'::interval;
or
SELECT DATA FROM <tbl> WHERE ID = 2 AND TIME > now() - '1 week'::interval;
Since I have about 350000 rows the last 24 hours the query planner chooses
to use my ID-index to get hold of the rows - then using only a filter on
the time column.
This takes a lot of time (over a minute) on a P4 1900MHz which
unfortenately isn't good enough for my purpose (webpages times out and so
on..).
If I SELECT only the rows with a certain ID (regardless of time):
SELECT DATA FROM <tbl> WHERE ID = 3;
..it still takes almost a minute so I guess this is the problem (not the
filtering on the TIME-column), especially since it recieves a lot of rows
which will be descarded using my filter anyway.
(I recieve ~6000 rows and want about 250).
But using the TIME-column as a first subset of rows and discarding using
the ID-column as a filter is even worse since I then get 350k rows and
discards about 349750 of them using the filter.
I tried applying a multicolumn index on ID and TIME, but that one won't
even be used (after ANALYZE).
My only option here seems to have like a "daily" table which will only
carry the rows for the past 24 hours which will give my SELECT a result of
6000 initial rows out of ~350k (instead of 14M like now) and then 250 when
filtered.
But I really hope there is a cleaner solution to the problem - actually I
though a multicolumn index would do it.
-ra
