postgresql – 如何使用多列中的值分发表？

根据 the Citus documentation,使用单列分发表很容易：

SELECT master_create_distributed_table('github_events','created_at','append');

有没有办法使用多列分发表？例如,类似于：

SELECT master_create_distributed_table('github_events','user_id,site_id','append');

解决方法

Citus不支持按多列分发.但是,您可以创建一个复合类型和 partition your data by that composite type.

– 如果链接失效,下面将链接内容链接 –

在复合类型上进行散列分区的步骤

>在主节点和所有工作节点上创建类型：

CREATE TYPE new_composite_type as (project_key text,date text);

>创建用于检查相等性的函数,并将其与新类型的相等运算符相关联

CREATE FUNCTION equal_test_composite_type_function(new_composite_type,new_composite_type) RETURNS boolean
AS 'select $1.project_key = $2.project_key AND $1.date = $2.date;'
LANGUAGE sql
IMMUTABLE
RETURNS NULL ON NULL INPUT;

-- ... use that function to create a custom equality operator...
CREATE OPERATOR = (
    LEFTARG = new_composite_type,RIGHTARG = new_composite_type,PROCEDURE = equal_test_composite_type_function,HASHES
);

>创建一个新的哈希函数.

注意：这只是一个简单的例子,可能无法提供良好的均匀哈希分布.有几个好的散列函数的例子可以在一个单独的C函数而不是sql中实现.

CREATE FUNCTION new_composite_type_hash(new_composite_type) RETURNS int
AS 'SELECT hashtext( ($1.project_key || $1.date)::text);'   
LANGUAGE sql
IMMUTABLE
RETURNS NULL ON NULL INPUT;

>为BTREE和HASH访问方法定义运算符类：

CREATE OPERATOR CLASS new_op_fam_btree_class
DEFAULT FOR TYPE new_composite_type USING BTREE AS
OPERATOR 3 = (new_composite_type,new_composite_type);

CREATE OPERATOR CLASS new_op_fam_hash_class
DEFAULT FOR TYPE new_composite_type USING HASH AS
OPERATOR 1 = (new_composite_type,new_composite_type),FUNCTION 1 new_composite_type_hash(new_composite_type);

>使用新类型创建表并分发它.

CREATE TABLE composite_type_partitioned_table
(
    id integer,composite_column new_composite_type
);

SELECT master_create_distributed_table('composite_type_partitioned_table','composite_column','hash');

SELECT master_create_worker_shards('composite_type_partitioned_table',4,1);

>运行INSERT和SELECT.请注意,正确的修剪将需要引用,如这些查询中所示.

INSERT INTO composite_type_partitioned_table VALUES  (1,'("key1","20160101")'::new_composite_type);
INSERT INTO composite_type_partitioned_table VALUES  (2,"20160102")'::new_composite_type);
INSERT INTO composite_type_partitioned_table VALUES  (3,'("key2","20160101")'::new_composite_type);
INSERT INTO composite_type_partitioned_table VALUES  (4,"20160102")'::new_composite_type);

SELECT * FROM composite_type_partitioned_table WHERE composite_column =  '("key1","20160101")'::new_composite_type;

UPDATE composite_type_partitioned_table SET id = 6 WHERE composite_column =  '("key2","20160101")'::new_composite_type;

SELECT * FROM composite_type_partitioned_table WHERE composite_column =  '("key2","20160101")'::new_composite_type;

其他说明：

有两个注意事项要警惕：

>必须正确分隔输入文件以允许copy_to_distributed_table工作.为此,请使用COPY(SELECT():: composite_type_field,….);从普通表到文件然后加载.>对于修剪以使用选择查询,复合类型字段应使用引号.

postgresql – 如何使用多列中的值分发表？

解决方法

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