On Jul 21, 2006, at 12:17 PM, Kevin Keith wrote:
I have a case where I am partitioning tables based on a date range
in version 8.1.4. For example:
table_with_millions_of_records
interaction_id char(16) primary key
start_date timestamp (without timezone) - indexed
.. other columns
child_1 start_date >= 2006-07-21 00:00:00
child_2 start_date >= 2006-07-20 00:00:00 and start_date <
2006-07-21 00:00:00
...
child_5 start_date >= 2006-07-17 00:00:00 and start_date <
2006-07-18 00:00:00
with rules on the parent and child tables that redirect the data to
the appropriate child table based on the start_date.
Because this table is going to grow very large (very quickly), and
will need to be purged daily, I created partitions, or child tables
to hold data for each day. I have done the same thing in Oracle in
the past, and the PostgreSQL solution works great. The archival
process is very simple - drop the expired child table. I am having
one problem.
If I run a query on the full table (there are 5 child tables with
data for the last 5 days), and my where clause contains data for
the current day only:
where start_date > date_trunc('day', now())
all 5 child tables are scanned when I look at the output from
explain analyze.
My question is - can I force the planner to only scan the relevant
child table - when the key related to the partitioned data it part
of the where clause?
Yes. You'll need non-overlapping check constraints in each child
table and to set constraint_exclusion to "on" in postgresql.conf.
See http://www.postgresql.org/docs/8.1/static/ddl-partitioning.html
for the gory details.
Cheers,
Steve
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TIP 6: explain analyze is your friend
