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86 lines
3.1 KiB
Markdown
86 lines
3.1 KiB
Markdown
---
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toc_priority: 30
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toc_title: MaterializedPostgreSQL
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---
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# [experimental] MaterializedPostgreSQL {#materialize-postgresql}
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使用PostgreSQL数据库表的初始数据转储创建ClickHouse数据库，并启动复制过程，即执行后台作业，以便在远程PostgreSQL数据库中的PostgreSQL数据库表上发生新更改时应用这些更改。
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ClickHouse服务器作为PostgreSQL副本工作。它读取WAL并执行DML查询。DDL不是复制的，但可以处理（如下所述）。
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## 创建数据库 {#creating-a-database}
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``` sql
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CREATE DATABASE [IF NOT EXISTS] db_name [ON CLUSTER cluster]
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ENGINE = MaterializedPostgreSQL('host:port', ['database' | database], 'user', 'password') [SETTINGS ...]
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```
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**Engine参数**
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- `host:port` — PostgreSQL服务地址
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- `database` — PostgreSQL数据库名
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- `user` — PostgreSQL用户名
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- `password` — 用户密码
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## 设置 {#settings}
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- [materialized_postgresql_max_block_size](../../operations/settings/settings.md#materialized-postgresql-max-block-size)
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- [materialized_postgresql_tables_list](../../operations/settings/settings.md#materialized-postgresql-tables-list)
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- [materialized_postgresql_allow_automatic_update](../../operations/settings/settings.md#materialized-postgresql-allow-automatic-update)
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``` sql
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CREATE DATABASE database1
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ENGINE = MaterializedPostgreSQL('postgres1:5432', 'postgres_database', 'postgres_user', 'postgres_password')
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SETTINGS materialized_postgresql_max_block_size = 65536,
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materialized_postgresql_tables_list = 'table1,table2,table3';
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SELECT * FROM database1.table1;
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```
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## 必备条件 {#requirements}
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- 在postgresql配置文件中将[wal_level](https://www.postgresql.org/docs/current/runtime-config-wal.html)设置为`logical`，将`max_replication_slots`设置为`2`。
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- 每个复制表必须具有以下一个[replica identity](https://www.postgresql.org/docs/10/sql-altertable.html#SQL-CREATETABLE-REPLICA-IDENTITY):
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1. **default** (主键)
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2. **index**
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``` bash
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postgres# CREATE TABLE postgres_table (a Integer NOT NULL, b Integer, c Integer NOT NULL, d Integer, e Integer NOT NULL);
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postgres# CREATE unique INDEX postgres_table_index on postgres_table(a, c, e);
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postgres# ALTER TABLE postgres_table REPLICA IDENTITY USING INDEX postgres_table_index;
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```
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总是先检查主键。如果不存在，则检查索引(定义为副本标识索引)。
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如果使用index作为副本标识，则表中必须只有一个这样的索引。
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你可以用下面的命令来检查一个特定的表使用了什么类型:
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``` bash
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postgres# SELECT CASE relreplident
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WHEN 'd' THEN 'default'
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WHEN 'n' THEN 'nothing'
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WHEN 'f' THEN 'full'
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WHEN 'i' THEN 'index'
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END AS replica_identity
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FROM pg_class
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WHERE oid = 'postgres_table'::regclass;
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```
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## 注意 {#warning}
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1. [**TOAST**](https://www.postgresql.org/docs/9.5/storage-toast.html)不支持值转换。将使用数据类型的默认值。
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## 使用示例 {#example-of-use}
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``` sql
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CREATE DATABASE postgresql_db
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ENGINE = MaterializedPostgreSQL('postgres1:5432', 'postgres_database', 'postgres_user', 'postgres_password');
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SELECT * FROM postgresql_db.postgres_table;
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```
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