背景
已有分区表，修改分区的范围。
例如拆分分区，合并分区。
语法如下，PG支持非常灵活的分区布局，看本文提到的HASH分区拆分，支持任意层级的分区，支持每个分区的层级深度不一样。特别适合某些数据分布不均匀的情况。例如id=1落在同一个分区但是数据量非常庞大，可以对这个分区再进行二级分区（使用其他分区方法，其他字段都可以，非常灵活）。
ALTER TABLE [ IF EXISTS ] nameATTACH PARTITION partition_name { FOR VALUES partition_bound_spec | DEFAULT }ALTER TABLE [ IF EXISTS ] nameDETACH PARTITION partition_nameand partition_bound_spec is:IN ( partition_bound_expr [, ...] ) |FROM ( { partition_bound_expr | MINVALUE | MAXVALUE } [, ...] )TO ( { partition_bound_expr | MINVALUE | MAXVALUE } [, ...] ) |WITH ( MODULUS numeric_literal, REMAINDER numeric_literal )
拆分已有分区例子(hash)
1、创建一个哈希分区表，4个分区
postgres=# create table t_hash (id int , info text) PARTITION BY hash (id); CREATE TABLE postgres=# create table t_hash0 partition of t_hash FOR VALUES with (MODULUS 4, REMAINDER 0); CREATE TABLE postgres=# create table t_hash1 partition of t_hash FOR VALUES with (MODULUS 4, REMAINDER 1); CREATE TABLE postgres=# create table t_hash2 partition of t_hash FOR VALUES with (MODULUS 4, REMAINDER 2); CREATE TABLE postgres=# create table t_hash3 partition of t_hash FOR VALUES with (MODULUS 4, REMAINDER 3); CREATE TABLE
2、查看分区表
postgres=# \d+ t_hashPartitioned table "public.t_hash"Column | Type | Collation | Nullable | Default | Storage | Stats target | Description--------+---------+-----------+----------+---------+----------+--------------+-------------id | integer | | | | plain | |info | text | | | | extended | |Partition key: HASH (id)Partitions: t_hash0 FOR VALUES WITH (modulus 4, remainder 0),t_hash1 FOR VALUES WITH (modulus 4, remainder 1),t_hash2 FOR VALUES WITH (modulus 4, remainder 2),t_hash3 FOR VALUES WITH (modulus 4, remainder 3)
3、插入一些记录
postgres=# insert into t_hash select generate_series(1,10);INSERT 0 10
4、查看每一条记录属于哪个分区
postgres=# select tableoid::regclass,* from t_hash;tableoid | id | info----------+----+------t_hash0 | 1 |t_hash1 | 3 |t_hash1 | 5 |t_hash1 | 8 |t_hash1 | 9 |t_hash2 | 2 |t_hash3 | 4 |t_hash3 | 6 |t_hash3 | 7 |t_hash3 | 10 |(10 rows)
5、将1号分区拆分为2个分区。按8取模，把1号分区拆分成一个分区表（即1号分区被一个耳机分区表代替。而其他分区是直接的分区表，所以看起来就像一颗非平衡树）
4(0) , 4(1) , 4(2) , 4(3)拆分为4(0) , 4(1){8(1) , 8(5)} , 4(2) , 4(3)
解绑分区
postgres=# alter table t_hash DETACH PARTITION t_hash1;ALTER TABLE
创建二级分区
postgres=# create table t_hash1_subp (id int, info text) PARTITION BY hash (id);;CREATE TABLEpostgres=# create table t_hash1_subp1 partition of t_hash1_subp FOR VALUES with (MODULUS 8, REMAINDER 1);CREATE TABLEpostgres=# create table t_hash1_subp5 partition of t_hash1_subp FOR VALUES with (MODULUS 8, REMAINDER 5);CREATE TABLE
绑定二级分区到一级分区。
postgres=# alter table t_hash attach partition t_hash1_subp FOR VALUES WITH ( MODULUS 4, REMAINDER 1 );ALTER TABLE
将原来子分区的数据写入新的二级分区表(数据迁移)
postgres=# insert into t_hash1_subp select * from t_hash1;INSERT 0 4
查看记录，并列出记录所在分区名
postgres=# select tableoid::regclass,* from t_hash;tableoid | id | info---------------+----+------t_hash0 | 1 |t_hash1_subp1 | 3 |t_hash1_subp5 | 5 |t_hash1_subp5 | 8 |t_hash1_subp5 | 9 |t_hash2 | 2 |t_hash3 | 4 |t_hash3 | 6 |t_hash3 | 7 |t_hash3 | 10 |(10 rows)
列出非平衡的分区表
postgres=# \d+ t_hashPartitioned table "public.t_hash"Column | Type | Collation | Nullable | Default | Storage | Stats target | Description--------+---------+-----------+----------+---------+----------+--------------+-------------id | integer | | | | plain | |info | text | | | | extended | |Partition key: HASH (id)Partitions: t_hash0 FOR VALUES WITH (modulus 4, remainder 0),t_hash1_subp FOR VALUES WITH (modulus 4, remainder 1), PARTITIONED,t_hash2 FOR VALUES WITH (modulus 4, remainder 2),t_hash3 FOR VALUES WITH (modulus 4, remainder 3)
扩展阅读，甚至我们可以把其他分区改成别的分区方法，例如将t_hash2改成list分区
postgres=# alter table t_hash detach partition t_hash2;ALTER TABLEpostgres=# create table t_hash2_subp (id int, info text) partition by list (info);CREATE TABLEpostgres=# create table t_hash2_supb1 partition of t_hash2_subp FOR VALUES in ('hello');CREATE TABLEpostgres=# create table t_hash2_supb2 partition of t_hash2_subp FOR VALUES in ('abc','cde');CREATE TABLEpostgres=# create table t_hash2_supb3 partition of t_hash2_subp DEFAULT;CREATE TABLEpostgres=# alter table t_hash attach partition t_hash2_subp for values with (modulus 4, remainder 2);ALTER TABLEpostgres=# \d+ t_hashPartitioned table "public.t_hash"Column | Type | Collation | Nullable | Default | Storage | Stats target | Description--------+---------+-----------+----------+---------+----------+--------------+-------------id | integer | | | | plain | |info | text | | | | extended | |Partition key: HASH (id)Partitions: t_hash0 FOR VALUES WITH (modulus 4, remainder 0),t_hash1_subp FOR VALUES WITH (modulus 4, remainder 1), PARTITIONED,t_hash2_subp FOR VALUES WITH (modulus 4, remainder 2), PARTITIONED,t_hash3 FOR VALUES WITH (modulus 4, remainder 3)postgres=# insert into t_hash select id,'abc' from t_hash2;INSERT 0 1postgres=# insert into t_hash select id,'def' from t_hash2;INSERT 0 1postgres=# insert into t_hash select id,'hello' from t_hash2;INSERT 0 1postgres=# select tableoid::regclass,* from t_hash;tableoid | id | info---------------+----+-------t_hash0 | 1 |t_hash1_subp1 | 3 |t_hash1_subp5 | 5 |t_hash1_subp5 | 8 |t_hash1_subp5 | 9 |t_hash2_supb2 | 2 | abct_hash2_supb1 | 2 | hellot_hash2_supb3 | 2 | deft_hash3 | 4 |t_hash3 | 6 |t_hash3 | 7 |t_hash3 | 10 |(12 rows)
拆分已有分区例子(range)
and partition_bound_spec is:IN ( partition_bound_expr [, ...] ) |FROM ( { partition_bound_expr | MINVALUE | MAXVALUE } [, ...] )TO ( { partition_bound_expr | MINVALUE | MAXVALUE } [, ...] ) |WITH ( MODULUS numeric_literal, REMAINDER numeric_literal )
合并已有分区例子(hash)
合并已有分区例子(range)
小结
4(0) , 4(1) , 4(2) , 4(3)拆分为4(0) , 4(1){8(1) , 8(5)} , 4(2) , 4(3)
