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Partitioning by composite key
Dmitry Ivanov edited this page Jun 6, 2017
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3 revisions
Release 1.4 also supports composite keys (which are expressions too).
/* create a table we're going to partition */
create table test (logdate date not null, comment text);
/* create sequence for automatic partition naming */
select create_naming_sequence('test');
/* we have to manually create a composite partitioning key */
create type test_key as (year float8, month float8);
/* register a RANGE-partitioned table 'test' */
select add_to_pathman_config('test',
'( extract(year from logdate),
extract(month from logdate) )::test_key',
NULL);
/* add one partition [(year, month), (year + 10, month)) */
select add_range_partition('test',
(extract(year from current_date), 1)::test_key,
(extract(year from current_date + '10 years'::interval), 1)::test_key);First of all, let's check the partition we've just created:
select parent, partition, parttype, range_min, range_max from pathman_partition_list ;
parent | partition | parttype | range_min | range_max
--------+-----------+----------+-----------+-----------
test | test_1 | 2 | (2017,1) | (2027,1)
(1 row)We couldn't use neither create_range_partitions() nor create_hash_partitions(), since the first one requires that MAX & MIN aggregates and +/- operators be defined for the expression's type, while the second one cannot work without a hash-function (which we didn't assign).
This means that we have to create new partitions manually. Let's add a few more:
/* [(10, 1), (20, 1)), [(20, 1), (30,1)) ... */
select add_range_partition('test',
(extract(year from current_date +
format('%s years', i)::interval),
1)::test_key,
(extract(year from current_date +
format('%s years', i + 10)::interval),
1)::test_key)
from generate_series(10, 200, 10) as g(i);That's way better!
select parent, partition, range_min, range_max
from pathman_partition_list
where parent = 'test'::regclass;
parent | partition | range_min | range_max
--------+-----------+-----------+-----------
test | test_1 | (2017,1) | (2027,1)
test | test_2 | (2027,1) | (2037,1)
test | test_3 | (2037,1) | (2047,1)
test | test_4 | (2047,1) | (2057,1)
test | test_5 | (2057,1) | (2067,1)
test | test_6 | (2067,1) | (2077,1)
test | test_7 | (2077,1) | (2087,1)
test | test_8 | (2087,1) | (2097,1)
test | test_9 | (2097,1) | (2107,1)
test | test_10 | (2107,1) | (2117,1)
test | test_11 | (2117,1) | (2127,1)
test | test_12 | (2127,1) | (2137,1)
test | test_13 | (2137,1) | (2147,1)
test | test_14 | (2147,1) | (2157,1)
test | test_15 | (2157,1) | (2167,1)
test | test_16 | (2167,1) | (2177,1)
test | test_17 | (2177,1) | (2187,1)
test | test_18 | (2187,1) | (2197,1)
test | test_19 | (2197,1) | (2207,1)
test | test_20 | (2207,1) | (2217,1)
test | test_21 | (2217,1) | (2227,1)
(21 rows)Note that overlap checks will still work:
/* this command will fail */
select add_range_partition('test',
(extract(year from current_date + '30 years'::interval), 1)::test_key,
(extract(year from current_date + '50 years'::interval), 1)::test_key);
ERROR: specified range [(2047,1), (2067,1)) overlaps with existing partitionsThe expression itself looks quite ugly:
ROW(date_part('year'::text, logdate), date_part('month'::text, logdate))::test_keyUnfortunately, we can't do much about it. Let's select all dates prior to (2040, 1):
explain select * from test
where ROW(date_part('year'::text, logdate),
date_part('month'::text, logdate))::test_key < (2040, 1)::test_key;
QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Append (cost=0.00..83.98 rows=2963 width=36)
-> Seq Scan on test_1 (cost=0.00..22.70 rows=1270 width=36)
-> Seq Scan on test_2 (cost=0.00..22.70 rows=1270 width=36)
-> Seq Scan on test_3 (cost=0.00..38.58 rows=423 width=36)
Filter: (ROW(date_part('year'::text, (logdate)::timestamp without time zone), date_part('month'::text (logdate)::timestamp without time zone))::test_key < ROW('2040'::double precision, '1'::double precision)::test_key)
(5 rows)The harshest limitations:
- The following functions won't work with composite keys by default:
create_range_partitions()create_hash_partitions()append_range_partition()prepend_range_partition()generate_range_bounds()
- Automatic partition creation on
INSERTis disabled; - All other limitations that are inherent to expressions;