CnosDB FDW：打通一扇通往PostgreSQL世界的大门

本文档提供了下载、安装和使用 CnosDB FDW 的简要说明。请根据您的实际需求和环境对文档进行调整。

概述

CnosDB FDW 是一个用于在 PostgreSQL 数据库中访问 CnosDB 数据库的外部数据包装器（Foreign Data Wrapper）。它提供了在 PostgreSQL 中查询 CnosDB 数据的功能。

本文档将指导您下载、安装和使用 CnosDB FDW。

下载

方法一

git clone git@github.com:cnosdb/wrappers.git
cd wrappers/wrappers

CnosDB FDW依赖pgrx，在安装之前需要先安装pgrx，可以参考官方仓库readme [
https://github.com/pgcentralfoundation/pgrx#system-requirements]。

pgrx安装完毕后，运行以下命令：

cargo pgrx install --pg-config [path_to_pg_config] --features cnosdb_fdw

方法二

release[
https://github.com/cnosdb/wrappers/releases]下载对应系统的动态库，放置到Postgres对应目录

$PATH_TO_PG/share/extension/wrappers.control

$PATH_TO_PG/lib/wrappers-0.1.18.so

$PATH_TO_PG/share/extension/wrappers–0.1.18.sql

用例

准备CnosDB数据

启动CnosDB server和client，在client中输入以下SQL：

CREATE TABLE air (
      visibility DOUBLE,
      temperature DOUBLE,
      pressure DOUBLE,
      TAGS(station)
);

INSERT INTO air (time, station, visibility, temperature, pressure) VALUES('2023-01-01 01:10:00', 'XiaoMaiDao', 79, 80, 63);

INSERT INTO air (time, station, visibility, temperature, pressure) VALUES('2023-01-01 01:20:00', 'XiaoMai', 80, 60, 62);

INSERT INTO air (time, station, visibility, temperature, pressure) VALUES('2023-01-01 01:30:00', 'Xiao', 81, 70, 61);

执行查询SQL：

SELECT * FROM air;

public ❯ select * from air;
+---------------------+------------+------------+-------------+----------+
| time                | station    | visibility | temperature | pressure |
+---------------------+------------+------------+-------------+----------+
| 2023-01-01T01:10:00 | XiaoMaiDao | 79.0       | 80.0        | 63.0     |
| 2023-01-01T01:20:00 | XiaoMai    | 80.0       | 60.0        | 62.0     |
| 2023-01-01T01:30:00 | Xiao       | 81.0       | 70.0        | 61.0     |
+---------------------+------------+------------+-------------+----------+

使用Postgres查询CnosDB数据

创建CnosDB外部表

-- create extension
create extension wrappers;

SELECT * FROM pg_extension;

-- create foreign data wrapper and enable 'CnosdbFdw'
CREATE FOREIGN DATA WRAPPER cnosdb_wrapper
HANDLER cnosdb_fdw_handler
VALIDATOR cnosdb_fdw_validator;

SELECT * FROM pg_foreign_data_wrapper;

-- create server and specify custom options
CREATE SERVER my_cnosdb_server
FOREIGN DATA WRAPPER cnosdb_wrapper
OPTIONS (
    url 'http://localhost:8904',
    username 'root',
    password '',
    tenant 'cnosdb',
    db 'public'
);

-- create an example foreign table
CREATE FOREIGN TABLE air(
    time timestamp,
    station text,
    visibility double precision,
    temperature double precision,
    pressure double precision
)
SERVER my_cnosdb_server
OPTIONS (
    table 'air'
);

查询CnosDB数据

SELECT * FROM air;

postgres=# select * from air;
        time         |  station   | visibility | temperature | pressure
---------------------+------------+------------+-------------+----------
 2023-01-01 01:30:00 | Xiao       |         81 |          70 |       61
 2023-01-01 01:20:00 | XiaoMai    |         80 |          60 |       62
 2023-01-01 01:10:00 | XiaoMaiDao |         79 |          80 |       63
(3 rows)