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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，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，请跟着小编一起来学习吧！
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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.
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 INDEX
FOREIGN 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.
到此，关于“PostgreSQL11有哪些新特性”的学习就结束了，希望能够解决大家的疑惑。理论与实践的搭配能更好的帮助大家学习，快去试试吧！若想继续学习更多相关知识，请继续关注创新互联网站，小编会继续努力为大家带来更多实用的文章！
