GLOBAL INDEX是分区表上的一种索引技术,可以创建在分区表的非分区键上,也支持提供唯一约束。
语法
CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ [ IF NOT EXISTS ] name ] ON [ ONLY ] table_name [ USING method ]
( { column_name | ( expression ) } [ COLLATE collation ] [ opclass [ ( opclass_parameter = value [, ... ] ) ] ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ] [, ...] )
[ INCLUDE ( column_name [, ...] ) ]
[ WITH ( storage_parameter [= value] [, ... ] ) ]
[ GLOBAL/LOCAL/global_partitioned_index ]
[ TABLESPACE tablespace_name ]
[ WHERE predicate ]
global_partitioned_index:
GLOBAL PARTITION BY {RANGE (column_list) (index_partitioning_clause) |
HASH (column_list) (hash_partitions_by_quantity)}
说明
GLOBAL/LOCAL
参数指定为GLOBAL
即创建GLOBAL INDEX。- 如果不指定创建
GLOBAL/LOCAL
参数,则默认创建LOCAL INDEX。 - GLOBAL INDEX的CREATE语法支持使用CONCURRENTLY模式创建。
- 非分区表、包括分区表的子表上不支持创建GLOBAL INDEX。
- GLOBAL INDEX不支持表达式索引。
- 无法在分区表的分区列上创建GLOBAL INDEX。
GLOBAL INDEX拥有以下优势:
- 能提供分区表中非分区列上的唯一约束。
- 带分区表的查询但没有指定分区键场景,用于加速查询的性能,即分区键外的第二查找键。
- 跨机并行查询支持加速创建B-Tree索引的GLOBAL索引,详情请参见使用跨机并行查询加速索引创建。
全局分区索引(Global Partitioned Index):
- Global Partitioned Index支持将GLOBAL INDEX进行range或hash分区,分区的语法和partition table类似。
- Global Partitioned Index不支持按照List分区。
- Global Partitioned Index只支持在分区表主表上创建,支持创建在分区键的列上。
- Global Partitioned Index支持全局唯一约束。
- Global Partitioned Index分区列必须指定索引列的左前缀。
- Global Partitioned range Index支持有序扫描。
- Global Partitioned hash Index不支持有序扫描。
- Global Partitioned hash Index只有等指值表达式支持索引剪枝优化。
- Global Partitioned Index支持索引剪枝优化,即优化器剪枝和执行器剪枝。
示例
分区表使用时间分区,定期创建新分区,淘汰老分区。
CREATE TABLE partition_range ( id integer,
a int,
b int,
created_date timestamp without time zone
)
PARTITION BY RANGE (created_date);
CREATE TABLE partition_range_part01 (
id integer,
a int,
b int,
created_date timestamp without time zone
);
ALTER TABLE ONLY partition_range ATTACH PARTITION partition_range_part01 FOR VALUES FROM (MINVALUE) TO ('2020-01-01 00:00:00');
CREATE TABLE partition_range_part02 (
id integer,
a int,
b int,
created_date timestamp without time zone
);
ALTER TABLE ONLY partition_range ATTACH PARTITION partition_range_part02 FOR VALUES FROM ('2020-01-01 00:00:00') TO ('2020-02-01 00:00:00');
CREATE TABLE partition_range_part03 (
id integer,
a int,
b int,
created_date timestamp without time zone
);
ALTER TABLE ONLY partition_range ATTACH PARTITION partition_range_part03 FOR VALUES FROM ('2020-02-01 00:00:00') TO ('2020-03-01 00:00:00');
当分区表较多时,部分查询如果不指定分区键created_date
,则查询性能会较差。
SELECT * FROM partition_range WHERE id = $1
此时创建GLOBAL INDEX,查询性能可以获得较大提升,创建GLOBAL INDEX语句如下:
CREATE UNIQUE INDEX idx_partition_range_global ON partition_range(id) global;
创建GLOBAL INDEX后,查询性能如下:
EXPLAIN (costs off) SELECT * FROM partition_range WHERE ID = 6;
QUERY PLAN
-----------------------------------------------------------------------
Global Index Scan using idx_partition_range_global on partition_range
Index Cond: (id = 6)
(2 rows)
在有GLOBAL INDEX的分区表上,依然支持ATTACH和DETACH分区:
- ATTACH新分区
CREATE TABLE partition_range_part06 ( id integer, a int, b int, created_date timestamp without time zone ); ALTER TABLE ONLY partition_range ATTACH PARTITION partition_range_part06 FOR VALUES FROM ('2020-05-01 00:00:00') TO ('2020-06-01 00:00:00');
- DETACH老分区
ALTER TABLE partition_range DETACH PARTITION partition_range_part01;
创建Global partition unique range index:
CREATE TABLE partition_range (
a int,
b int,
id integer,
created_date timestamp without time zone
)
PARTITION BY RANGE (created_date);
CREATE TABLE partition_range_part01 (
a int,
b int,
id integer,
created_date timestamp without time zone
);
ALTER TABLE ONLY partition_range ATTACH PARTITION partition_range_part01 FOR VALUES FROM (MINVALUE) TO ('2020-01-01 00:00:00');
CREATE TABLE partition_range_part02 (
a int,
b int,
id integer,
created_date timestamp without time zone
);
ALTER TABLE ONLY partition_range ATTACH PARTITION partition_range_part02 FOR VALUES FROM ('2020-01-01 00:00:00') TO ('2020-02-01 00:00:00');
CREATE UNIQUE INDEX idx_partition_range_global ON partition_range(id) global
PARTITION BY range (id)
(
PARTITION idx_gpi_1_min_5 values less than(5),
PARTITION idx_gpi_2_5_10 values less than(10),
PARTITION idx_gpi_3_10_max values less than(maxvalue)
);
创建Global Partition unique hash Index:
CREATE UNIQUE INDEX global_hash_idx ON partition_range(id) global
PARTITION BY HASH(id) PARTITIONS 8;
剪枝优化。
- Global Partition range Index优化器剪枝:范围条件剪枝。
显示结果如下:explain (costs off) select id, to_char(created_date, 'YYYYMMDD') from partition_range where id >= 5 and id < 7;
QUERY PLAN ---------------------------------------------------------------------------------------- Global Partitioned Index Scan(1/3) using idx_partition_range_global on partition_range Index Cond: ((id >= 5) AND (id < 7)) (2 rows)
- Global Partition hash Index优化器剪枝:等值条件剪枝。
显示结果如下:explain (costs off) select id, to_char(created_date, 'YYYYMMDD') from partition_range where id = 6;
QUERY PLAN ------------------------------------------------------------------------ Global Partitioned Index Scan(1/3) using idx_global on partition_range Index Cond: (id = 6) (2 rows)
- Global Partition Index执行剪枝:prepare语句使用执行器剪枝(initial prune)。
显示结果如下:INSERT INTO partition_range (id,a,b,created_date) VALUES(1, 1,1,'2020-01-02'); INSERT INTO partition_range (id,a,b,created_date) VALUES(2, 1,1,'2020-04-02'); INSERT INTO partition_range (id,a,b,created_date) VALUES(3, 1,1,'2020-02-02'); INSERT INTO partition_range (id,a,b,created_date) VALUES(4, 1,1,'2020-05-02'); INSERT INTO partition_range (id,a,b,created_date) VALUES(5, 1,1,'2020-03-02'); INSERT INTO partition_range (id,a,b,created_date) VALUES(6, 1,1,'2019-12-12'); INSERT INTO partition_range (id,a,b,created_date) VALUES(7, 1,1,'2020-05-02'); CREATE UNIQUE INDEX idx_partition_range_global ON partition_range(id) global PARTITION BY range (id) ( PARTITION idx_gpi_1_min_5 values less than(5), PARTITION idx_gpi_2_5_10 values less than(10), PARTITION idx_gpi_3_10_max values less than(maxvalue) ); set polar_comp_custom_plan_tries =0; prepare e1(int) as select * from partition_range where id = $1; EXECUTE e1(3);
NOTICE: global partitioned index idx_partition_range_global do initial prune (1/3) id | a | b | created_date ----+---+---+-------------------- 3 | 1 | 1 | 02-FEB-20 00:00:00 (1 row)
- Global Partition Index执行剪枝:prepare语句使用执行器剪枝(exec prune)。
显示结果如下:set polar_comp_custom_plan_tries =0; prepare e2(int,int) as select * from partition_range where id between $1 and $2 and id >= (select 6); EXECUTE e2(1,9);
NOTICE: global partitioned index idx_partition_range_global do exec prune (1/3) a | b | id | created_date ---+---+----+-------------------------- 1 | 1 | 6 | Thu Dec 12 00:00:00 2019 1 | 1 | 7 | Sat May 02 00:00:00 2020 (2 rows)
- Global Partition Index执行剪枝:子查询使用执行器剪枝(exec prune)。
显示结果如下:create table tbl1(col1 int); insert into tbl1 values (501), (505), (5); create table tprt (col1 int, col2 int) partition by range (col1); create table tprt_1 partition of tprt for values from (1) to (501); create table tprt_2 partition of tprt for values from (501) to (1001); create table tprt_3 partition of tprt for values from (1001) to (2001); insert into tprt values (10,501), (550,505),(20,5), (1010, 500); create index tprt1_idx on tprt_1 (col1); create index tprt2_idx on tprt_2 (col1); create index tprt3_idx on tprt_3 (col1); create index idx_global_tprt on tprt(col2) global PARTITION BY range (col2) ( PARTITION idx_global_tprt_less_100 values less than(100), PARTITION idx_global_tprt_101_200 values less than(200), PARTITION idx_global_tprt_201_max values less than(maxvalue) ); set enable_hashjoin = off; set enable_mergejoin = off; set enable_material=off; explain (costs off) select (select col1 from tprt a where a.col2 = b.col1) as x ,b.col1 from tbl1 b;
QUERY PLAN ---------------------------------------------------------------------------- Seq Scan on tbl1 b SubPlan 1 -> Global Partitioned Index Scan(3/3) using idx_global_tprt on tprt a Index Cond: (col2 = b.col1) (4 rows)
显示结果如下:select (select col1 from tprt a where a.col2 = b.col1) as x ,b.col1 from tbl1 b;
NOTICE: global partitioned index idx_global_tprt do exec prune (1/3) NOTICE: global partitioned index idx_global_tprt do exec prune (1/3) NOTICE: global partitioned index idx_global_tprt do exec prune (1/3) x | col1 -----+------ 10 | 501 550 | 505 20 | 5 (3 rows)
- Global Partition Index执行剪枝:多表join使用执行器剪枝(exec prune)。
显示结果如下:explain (costs off) select /*+ leading(b t) */ t.col2 ,b.col1 from tbl1 b, tprt t where t.col2 = b.col1;
NOTICE: prune partition child table tprt_1 after choose global index NOTICE: prune partition child table tprt_2 after choose global index NOTICE: prune partition child table tprt_3 after choose global index QUERY PLAN -------------------------------------------------------------------------- Nested Loop -> Seq Scan on tbl1 b -> Global Partitioned Index Scan(3/3) using idx_global_tprt on tprt t Index Cond: (col2 = b.col1) (4 rows)
显示结果如下:select /*+ leading(b t) */ t.col2 ,b.col1 from tbl1 b, tprt t where t.col2 = b.col1;
NOTICE: prune partition child table tprt_1 after choose global index NOTICE: prune partition child table tprt_2 after choose global index NOTICE: prune partition child table tprt_3 after choose global index NOTICE: global partitioned index idx_global_tprt do exec prune (1/3) NOTICE: global partitioned index idx_global_tprt do exec prune (1/3) NOTICE: global partitioned index idx_global_tprt do exec prune (1/3) col2 | col1 ------+------ 501 | 501 505 | 505 5 | 5 (3 rows)