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这篇文章主要介绍“PostgreSQL11 有哪些新特性”，在日常操作中，相信很多人在 PostgreSQL11 有哪些新特性问题上存在疑惑，丸趣 TV 小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答”PostgreSQL11 有哪些新特性”的疑惑有所帮助！接下来，请跟着丸趣 TV 小编一起来学习吧！
一、并行查询
Parallel Hash
Hash Join 执行时，在构造 Hash 表和进行 Hash 连接时，PG 11 可使用并行的方式执行。
测试脚本：
testdb=# create table t1 (c1 int,c2 varchar(40),c3 varchar(40));
CREATE TABLE
testdb=#
testdb=# insert into t1 select generate_series(1,5000000), TEST ||generate_series(1,1000000),generate_series(1,1000000)|| TEST
INSERT 0 5000000
testdb=# drop table if exists t2;
DROP TABLE
testdb=# create table t2 (c1 int,c2 varchar(40),c3 varchar(40));
CREATE TABLE
testdb=#
testdb=# insert into t2 select generate_series(1,1000000), T2 ||generate_series(1,1000000),generate_series(1,1000000)|| T2
INSERT 0 1000000
testdb=# explain verbose
testdb-# select t1.c1,t2.c1
testdb-# from t1 inner join t2 on t1.c1 = t2.c1;
QUERY PLAN
---------------------------------------------------------------------------------------------
Gather (cost=18372.00..107975.86 rows=101100 width=8)
Output: t1.c1, t2.c1
Workers Planned: 2 -- 2 Workers
- Parallel Hash Join (cost=17372.00..96865.86 rows=42125 width=8) -- Parallel Hash Join
Output: t1.c1, t2.c1
Hash Cond: (t1.c1 = t2.c1)
- Parallel Seq Scan on public.t1 (cost=0.00..45787.33 rows=2083333 width=4)
Output: t1.c1
- Parallel Hash (cost=10535.67..10535.67 rows=416667 width=4) -- Parallel Hash
Output: t2.c1
- Parallel Seq Scan on public.t2 (cost=0.00..10535.67 rows=416667 width=4)
Output: t2.c1除了 Parallel Hash 外,PG 11 在执行 Parallel Append(执行 UNION ALL 等集合操作)/CREATE TABLE AS SELECT/CREATE MATERIALIZED VIEW/SELECT INTO/CREATE INDEX 等操作时以并行的方式执行.
二、数据表分区
Hash Partition
PG 在 11.x 引入了 Hash 分区, 关于 Hash 分区, 官方文档有如下说明:
The table is partitioned by specifying a modulus and a remainder for each partition. Each partition will hold the rows for which the hash value of the partition key divided by the specified modulus will produce the specified remainder.
每个 Hash 分区需指定 模 (modulus)和 余 (remainder), 数据在哪个分区 (partition index) 的计算公式:
partition index = abs(hashfunc(key)) % modulus
drop table if exists t_hash2;
create table t_hash2 (c1 int,c2 varchar(40),c3 varchar(40)) partition by hash(c1);
create table t_hash2_1 partition of t_hash2 for values with (modulus 6,remainder 0);
create table t_hash2_2 partition of t_hash2 for values with (modulus 6,remainder 1);
create table t_hash2_3 partition of t_hash2 for values with (modulus 6,remainder 2);
create table t_hash2_4 partition of t_hash2 for values with (modulus 6,remainder 3);
create table t_hash2_5 partition of t_hash2 for values with (modulus 6,remainder 4);
create table t_hash2_6 partition of t_hash2 for values with (modulus 6,remainder 5);
testdb=# insert into t_hash2
testdb-# select generate_series(1,1000000), HASH ||generate_series(1,1000000),generate_series(1,1000000)|| HASH
INSERT 0 1000000数据在各分区上的分布大体均匀.
2018-9-19 注: 由于插入数据时语句出错, 昨天得出的结果有误(但数据在各个分区的分布上不太均匀,t_hash2_1 分区行数明显的比其他分区的要多很多), 请忽略
testdb=# select count(*) from only t_hash2;
; count
-------
0
(1 row)
testdb=# select count(*) from only t_hash2_1;
count
--------
166480
(1 row)
testdb=# select count(*) from only t_hash2_2;
count
--------
166904
(1 row)
testdb=# select count(*) from only t_hash2_3;
count
--------
166302
(1 row)
testdb=# select count(*) from only t_hash2_4;
count
--------
166783
(1 row)
testdb=# select count(*) from only t_hash2_5;
count
--------
166593
(1 row)
testdb=# select count(*) from only t_hash2_6;
count
--------
166938
(1 row)Hash 分区键亦可以创建在字符型字段上
testdb=# drop table if exists t_hash4;
DROP TABLE
testdb=# create table t_hash4 (c1 int,c2 varchar(40),c3 varchar(40)) partition by hash(c2);
CREATE TABLE
-- 需创建相应的 Partition 用于存储相应的数据
testdb=# insert into t_hash4
testdb-# select generate_series(1,100000), HASH ||generate_series(1,1000000),generate_series(1,1000000)|| HASH
ERROR: no partition of relation t_hash4 found for row
DETAIL: Partition key of the failing row contains (c2) = (HASH1).
-- 6 个分区,3 个 sub-table, 插入数据会出错
testdb=#
testdb=# create table t_hash4_1 partition of t_hash4 for values with (modulus 6,remainder 0);
CREATE TABLE
testdb=# create table t_hash4_2 partition of t_hash4 for values with (modulus 6,remainder 1);
CREATE TABLE
testdb=# create table t_hash4_3 partition of t_hash4 for values with (modulus 6,remainder 2);
CREATE TABLE
testdb=# insert into t_hash4
testdb-# select generate_series(1,10000), HASH ||generate_series(1,10000),generate_series(1,10000)|| HASH
ERROR: no partition of relation t_hash4 found for row
DETAIL: Partition key of the failing row contains (c2) = (HASH1).
-- 3 个分区,3 个 sub-table, 正常
testdb=# drop table if exists t_hash4;
DROP TABLE
testdb=# create table t_hash4 (c1 int,c2 varchar(40),c3 varchar(40)) partition by hash(c2);
CREATE TABLE
testdb=# create table t_hash4_1 partition of t_hash4 for values with (modulus 3,remainder 0);
CREATE TABLE
testdb=# create table t_hash4_2 partition of t_hash4 for values with (modulus 3,remainder 1);
CREATE TABLE
testdb=# create table t_hash4_3 partition of t_hash4 for values with (modulus 3,remainder 2);
CREATE TABLE
testdb=# insert into t_hash4
testdb-# select generate_series(1,10000), HASH ||generate_series(1,10000),generate_series(1,10000)|| HASH
INSERT 0 10000考察分区的数据分布, 还比较均匀:
testdb=#
testdb=# select count(*) from only t_hash4;
count
-------
0
(1 row)
testdb=# select count(*) from only t_hash4_1;
count
-------
3378
(1 row)
testdb=# select count(*) from only t_hash4_2;
count
-------
3288
(1 row)
testdb=# select count(*) from only t_hash4_3;
count
-------
3334
(1 row)Default Partition
List 和 Range 分区可指定 Default Partition(Hash 分区不支持).
Update partition key
PG 11 可 Update 分区键, 这会导致数据的 迁移 .
Create unique constraint
PG 11 在分区表上创建主键和唯一索引 (注:Oracle 在很早的版本已支持此特性).
在普通字段上可以创建 BTree 索引.
testdb=# alter table t_hash2 add primary key(c1);
ALTER TABLE
testdb=# create index idx_t_hash2_c2 on t_hash2(c2);
CREATE INDEXFOREIGN KEY support
PG 11 支持在分区上创建外键.
除了上述几个新特性外, 分区上面,PG 11 在 Automatic index creation/INSERT ON CONFLICT/Partition-Wise Join / Partition-Wise Aggregate/FOR EACH ROW trigger/Dynamic Partition Elimination/Control Partition Pruning 上均有所增强.
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