I'm implementing table partitioning on 8.2.5 -- I've got the tables set up
to partition based on the % 10 value of a key.
My problem is that I can't get the planner to take advantage of the
partitioning without also adding a key % 10 to the where clause.
Is there any way around that?
My child table definitions are:
CREATE TABLE topic_version_page_0 (
CHECK (topic_version_id % 10 = 0::integer )
) inherits (topic_version_page);
...
CREATE TABLE topic_version_page_9 (
CHECK (topic_version_id % 10 = 9::integer )
) inherits (topic_version_page);
I've also created indexes and constraints for each child table, and an
insert trigger on the master table (topic_version_page).
If I include a 'topic_version_id % 10 = [some value]' in my query, then the
partitioning shows up in the query plan:
test=> explain select * from topic_version_page where topic_version_id % 10
= (102 % 10) and topic_version_id = 102;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------
Result (cost=4.27..19.23 rows=2 width=194)
-> Append (cost=4.27..19.23 rows=2 width=194)
-> Bitmap Heap Scan on topic_version_page (cost=4.27..9.62 rows=1
width=194)
Recheck Cond: (topic_version_id = 102)
Filter: ((topic_version_id % 10) = 2)
-> Bitmap Index Scan on
index_topic_version_page_on_topic_version_id_and_created_at (cost=
0.00..4.27 rows=2 width=0)
Index Cond: (topic_version_id = 102)
-> Bitmap Heap Scan on topic_version_page_2 topic_version_page
(cost=4.27..9.62 rows=1 width=194)
Recheck Cond: (topic_version_id = 102)
Filter: ((topic_version_id % 10) = 2)
-> Bitmap Index Scan on
index_topic_version_page_2_on_topic_version_id_and_page_id
(cost=0.00..4.27rows=2 width=0)
Index Cond: (topic_version_id = 102)
(12 rows)
But if I don't explicitly include a 'topic_version_id % 10' -- the plan
gets much worse, checking every table (see below).
test=> explain select * from topic_version_page where topic_version_id =
102;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------
Result (cost=4.27..105.68 rows=22 width=194)
-> Append (cost=4.27..105.68 rows=22 width=194)
-> Bitmap Heap Scan on topic_version_page (cost=4.27..9.61 rows=2
width=194)
Recheck Cond: (topic_version_id = 102)
-> Bitmap Index Scan on
index_topic_version_page_on_topic_version_id_and_created_at (cost=
0.00..4.27 rows=2 width=0)
Index Cond: (topic_version_id = 102)
-> Bitmap Heap Scan on topic_version_page_0 topic_version_page
(cost=4.27..9.61 rows=2 width=194)
Recheck Cond: (topic_version_id = 102)
-> Bitmap Index Scan on
index_topic_version_page_0_on_topic_version_id_and_page_id
(cost=0.00..4.27rows=2 width=0)
Index Cond: (topic_version_id = 102)
-> Bitmap Heap Scan on topic_version_page_1 topic_version_page
(cost=4.27..9.61 rows=2 width=194)
Recheck Cond: (topic_version_id = 102)
-> Bitmap Index Scan on
index_topic_version_page_1_on_topic_version_id_and_page_id
(cost=0.00..4.27rows=2 width=0)
Index Cond: (topic_version_id = 102)
-> Bitmap Heap Scan on topic_version_page_2 topic_version_page
(cost=4.27..9.61 rows=2 width=194)
Recheck Cond: (topic_version_id = 102)
-> Bitmap Index Scan on
index_topic_version_page_2_on_topic_version_id_and_page_id
(cost=0.00..4.27rows=2 width=0)
Index Cond: (topic_version_id = 102)
-> Bitmap Heap Scan on topic_version_page_3 topic_version_page
(cost=4.27..9.61 rows=2 width=194)
Recheck Cond: (topic_version_id = 102)
-> Bitmap Index Scan on
index_topic_version_page_3_on_topic_version_id_and_page_id
(cost=0.00..4.27rows=2 width=0)
Index Cond: (topic_version_id = 102)
-> Bitmap Heap Scan on topic_version_page_4 topic_version_page
(cost=4.27..9.61 rows=2 width=194)
Recheck Cond: (topic_version_id = 102)
-> Bitmap Index Scan on
index_topic_version_page_4_on_topic_version_id_and_page_id
(cost=0.00..4.27rows=2 width=0)
Index Cond: (topic_version_id = 102)
-> Bitmap Heap Scan on topic_version_page_5 topic_version_page
(cost=4.27..9.61 rows=2 width=194)
Recheck Cond: (topic_version_id = 102)
-> Bitmap Index Scan on
index_topic_version_page_5_on_topic_version_id_and_page_id
(cost=0.00..4.27rows=2 width=0)
Index Cond: (topic_version_id = 102)
-> Bitmap Heap Scan on topic_version_page_6 topic_version_page
(cost=4.27..9.61 rows=2 width=194)
Recheck Cond: (topic_version_id = 102)
-> Bitmap Index Scan on
index_topic_version_page_6_on_topic_version_id_and_page_id
(cost=0.00..4.27rows=2 width=0)
Index Cond: (topic_version_id = 102)
-> Bitmap Heap Scan on topic_version_page_7 topic_version_page
(cost=4.27..9.61 rows=2 width=194)
Recheck Cond: (topic_version_id = 102)
-> Bitmap Index Scan on
index_topic_version_page_7_on_topic_version_id_and_page_id
(cost=0.00..4.27rows=2 width=0)
Index Cond: (topic_version_id = 102)
-> Bitmap Heap Scan on topic_version_page_8 topic_version_page
(cost=4.27..9.61 rows=2 width=194)
Recheck Cond: (topic_version_id = 102)
-> Bitmap Index Scan on
index_topic_version_page_8_on_topic_version_id_and_page_id
(cost=0.00..4.27rows=2 width=0)
Index Cond: (topic_version_id = 102)
-> Bitmap Heap Scan on topic_version_page_9 topic_version_page
(cost=4.27..9.61 rows=2 width=194)
Recheck Cond: (topic_version_id = 102)
-> Bitmap Index Scan on
index_topic_version_page_9_on_topic_version_id_and_page_id
(cost=0.00..4.27rows=2 width=0)
Index Cond: (topic_version_id = 102)
(46 rows)
Is there anyway to get the benefit of partitioning without adding a
additional 'topic_version_id % 10' condition to every query that touches
this table?
Thanks in advance.
Mason
