cassandra表设计

vjrehmav 于 2021-06-15 发布在 Cassandra

关注(0)|答案(2)|浏览(465)

我有如下数据：

select * from test;

 department | employee | batch_number | hash
------------+----------+--------------+-------
 dep1       | Bart     |            1 | hash1
 dep1       | Bart     |            1 | hash2
 dep1       | Lisa     |            3 | hash3
 dep1       | Lisa     |            4 | hash4
 dep1       | John     |            5 | hash5
 dep1       | Lucy     |            6 | hash6
 dep1       | Bart     |            7 | hash7
 dep1       | Bart     |            7 | hash8

我想用一个 where 条款 batch_number ，安 ordering 在 batch_number 和一个 in 上的 predicate employee .
在关系数据库中

select * from test 
  where department='dep1' 
  and employee in ('Bart','Lucy','John') 
  and batch_number >= 2 
  order by batch_number desc 
  limit 3;

 department | employee | batch_number | hash
------------+----------+--------------+-------
 dep1       | Bart     |            7 | hash7
 dep1       | Bart     |            7 | hash8
 dep1       | Lucy     |            6 | hash6

我在cassandra中为这个查询建模一个表时遇到了一些问题。 department 将是我的分区密钥 hash 必须是主键的一部分。但我正在努力使用集群键和/或（sstable-attached）辅助索引。
因为我要点菜 batch_number 我尝试将其作为群集密钥：

CREATE TABLE keyspace.test(
    department      TEXT,
    batch_number    INT,
    hash            TEXT,
    employee        TEXT,
    PRIMARY KEY ((department), batch_number, hash)
) WITH CLUSTERING ORDER BY (batch_number DESC);
CREATE INDEX tst_emp ON keyspace.test (employee);

但这不允许使用 in 我的索引上的 predicate ：

select * from keyspace.test where department='dep1' and employee in ('Bart','Lucy','John');
InvalidRequest: Error from server: code=2200 [Invalid query] message="IN predicates on non-primary-key columns (employee) is not yet supported"

所以我试着加入 employee 列作为群集键：

CREATE TABLE keyspace.test(
    department      TEXT,
    batch_number    INT,
    hash            TEXT,
    employee        TEXT,
    PRIMARY KEY ((department), batch_number, hash, employee)
) WITH CLUSTERING ORDER BY (batch_number DESC);

但这失败了，因为我不能把一个非情商关系 batch_number :

select * from keyspace.test where department='dep1' and batch_number > 1 and employee in ('Bart','Lucy','John');
InvalidRequest: Error from server: code=2200 [Invalid query] message="Clustering column "employee" cannot be restricted (preceding column "batch_number" is restricted by a non-EQ relation)"

但每当我把 employee 之前 batch_number 我失去了点餐的能力 batch_number :

CREATE TABLE keyspace.test(
    department      TEXT,
    employee        TEXT,
    batch_number    INT,
    hash            TEXT,
    PRIMARY KEY ((department), employee, batch_number, hash)
);

select * from keyspace.test where department='dep1' and employee in ('Bart','Lucy','John') ORDER BY batch_number DESC;
InvalidRequest: Error from server: code=2200 [Invalid query] message="Order by currently only support the ordering of columns following their declared order in the PRIMARY KEY"

那么什么样的表设计会允许这样的查询呢？这能在Cassandra做到吗？
编辑：
我希望能够在此表上运行的其他查询包括：

select * from keyspace.test where department='X' and batch_number=Y

以及

delete from keyspace.test where department='X'

sql cassandra database-design cql

来源：https://stackoverflow.com/questions/53223715/cassandra-table-design-for-query-with-order-limit-and-in-predicate

2条答案

按热度按时间

q9rjltbz1#

使用允许您重新排列数据的物化视图：

CREATE MATERIALIZED VIEW mv_test AS 
SELECT
   department,
   batch_number,
   employee,
   hash 
FROM
   test 
WHERE
   department IS NOT NULL 
   AND batch_number IS NOT NULL 
   AND employee IS NOT NULL 
   AND hash IS NOT NULL 
PRIMARY KEY (department, employee, batch_number, hash) 
WITH clustering 
ORDER BY
(batch_number DESC);

我可以执行以下查询：

SELECT * FROM mv_test 
WHERE
   department = 'dep1' 
   AND employee IN 
   (
      'Bart',
      'Lisa'
   )
   AND batch_number > 3;

结果按聚类顺序排列：

department | employee | batch_number | hash
------------+----------+--------------+-------
       dep1 |     Bart |            7 | hash7
       dep1 |     Bart |            7 | hash8
       dep1 |     Lisa |            4 | hash4

而 > 条款是不平等条款， IN ，虽然有多个值，但仍然是确定性的，这就是为什么我相信您可以毫无问题地筛选键。自 batch_number 是您最不希望筛选的内容，任何类型的where子句都是允许的。我想你一直 department .
请注意，物化视图会影响性能。更具体地说，写性能。但是，读取性能相对于 ALLOW FILTERING .
更新：
在物化视图末尾指定的顺序是 batch_number 但是，它将首先在 department ，那么 employee ，然后 batch_number ，所以 batch_number 具体来说是不保证的。据我所知，这是没有办法的。另一种数据库解决方案可能更可取。
更新2：
如apache邮件链中所述（参见下面的注解），物化视图并不被视为生产就绪。然而，datastax认为它们是可用的，前提是它们使用了上述最佳实践。就我个人而言，我对物化视图没有任何问题。当然，这是一个简单的单一数据中心集群，考虑到最佳实践中提到了更复杂的设置，它们在这种情况下可能会崩溃。

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w1e3prcc2#

您可以在 employee 如果需要，甚至可以从主键中删除它。你需要停止使用 IN 但是您可以拆分查询并在客户端连接结果。

CREATE TABLE tk.test_good(
    department      TEXT,
    batch_number    INT,
    employee        TEXT,
    hash            TEXT,
    PRIMARY KEY ((department), batch_number, hash)
)WITH CLUSTERING ORDER BY (batch_number DESC);

CREATE INDEX IF NOT EXISTS employee_idx ON tk.test_good ( employee );

select * from tk.test_good where department='dep1' and employee='Bart' and batch_number >= 2 limit 3;
select * from tk.test_good where department='dep1' and employee='Lucy' and batch_number >= 2 limit 3;
select * from tk.test_good where department='dep1' and employee='John' and batch_number >= 2 limit 3;

这种方法的缺点是索引可能会变得太大。但我不知道数据池的大小，所以我将留给您考虑。

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cassandra表设计

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