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Known limitations
This a non-exhaustive list of known limitations of pg_pathman:
Currently you can't create multilevel partitioning scheme.
create table test(id int not null, val float8);
create unique index on test (id);
select create_range_partitions('test', 'id', 1, 10, 3);
insert into test values (0, 0) on conflict (id) do update set val=1;
ERROR: ON CONFLICT clause is not supported with partitioned tablescreate table test(id int primary key, date timestamp not null);
select create_range_partitions('test', 'date', now(), '1 day'::interval, 4);
insert into test values(1, now());
insert into test values(1, now() + '1 day');
table test;
id | date
----+----------------------------
1 | 2017-10-03 16:33:24.953012
1 | 2017-10-04 16:33:31.476003
(2 rows)create table test(id int not null);
create unique index on test (id);
select create_range_partitions('test', 'id', 1, 10, 3);
insert into test values (1);
create table simple(id int references test(id));
insert into simple values (1);
ERROR: insert or update on table "simple" violates foreign key constraint "simple_id_fkey"
DETAIL: Key (id)=(1) is not present in table "test".This includes Londiste, pg_logical etc. Instead, take a look at pg_shardman.
Due to significant API changes, these optimizations are not available on 9.5:
- Faster partition pruning in
SELECT ...subqueries under UPDATE and DELETE statements; - Faster partition pruning in
SELECT ... FOR SHARE/UPDATE/etc.
See this page for more information.
We've noticed that certain queries cannot be planned by pg_pathman:
-
DELETE FROM partitioned_table_1 USING partitioned_table_2 ...; -
UPDATE partitioned_table_1 FROM partitioned_table_2 ...;
This is due to some limitations of PostgreSQL's planner: we can't hook inheritance planner used for DELETE and UPDATE queries on partitioned tables. As a result, we can't plan and execute queries that are going to modify several partitions:
create table a(val int not null);
select create_range_partitions('a', 'val', 1, 10, 3);
create table b(val int not null);
select create_range_partitions('b', 'val', 1, 10, 3);
delete from a using b where a.val = b.val;
ERROR: DELETE and UPDATE queries with a join of partitioned tables are not supportedHowever, query will work as expected if it's obvious to the planner that it wants to modify only 1 (or 0) partition:
explain (costs off)
delete from a using b where a.val = b.val and a.val < 10;
QUERY PLAN
-----------------------------------------
Delete on a_1
-> Merge Join
Merge Cond: (a_1.val = b_1.val)
-> Sort
Sort Key: a_1.val
-> Seq Scan on a_1
Filter: (val < 10)
-> Sort
Sort Key: b_1.val
-> Append
-> Seq Scan on b_1
-> Seq Scan on b_2
-> Seq Scan on b_3
(13 rows)As a workaround, you can use WITH statement to hide the joined partitioned table:
explain (costs off)
with q as (select * from b)
delete from a using q where a.val = q.val;
QUERY PLAN
---------------------------------------
Delete on a
Delete on a
Delete on a_1
Delete on a_2
Delete on a_3
CTE q
-> Append
-> Seq Scan on b_1
-> Seq Scan on b_2
-> Seq Scan on b_3
-> Hash Join
Hash Cond: (q.val = a.val)
-> CTE Scan on q
-> Hash
-> Seq Scan on a
-> Merge Join
Merge Cond: (a_1.val = q.val)
-> Sort
Sort Key: a_1.val
-> Seq Scan on a_1
-> Sort
Sort Key: q.val
-> CTE Scan on q
-> Merge Join
Merge Cond: (a_2.val = q.val)
-> Sort
Sort Key: a_2.val
-> Seq Scan on a_2
-> Sort
Sort Key: q.val
-> CTE Scan on q
-> Merge Join
Merge Cond: (a_3.val = q.val)
-> Sort
Sort Key: a_3.val
-> Seq Scan on a_3
-> Sort
Sort Key: q.val
-> CTE Scan on q
(39 rows)