openGauss/MogDB调用C FUNCTION

openGauss/MogDB 调用 C FUNCTION

摘要

之前写过一篇关于postgresql 自定义函数实现，通过 contrib 模块进行扩展的帖子，今天和恩墨工程师进行了一些交流，在 MogDB 中也可以实现同样的功能，原以为需要完整的 openGauss 的源码才能完成，但在恩墨工程师的指点下，了解到，通过既有官网版本的安装包就可以进行插件开发。而且，使用 postgres 的 C FUNCTION 要比开发插件更加容易些。也感谢恩墨专家提供的线索和思路

环境准备

安装 MogDB 参考官方文档，写的已经很详细了。

服务器环境 本地虚拟机 centos 7.9

注意：尽量进入omm用户下进行编译，可以避免一些不必要的环境问题

代码

C 代码 基本与 postgres 插件开发一样，关键是 4,5,6 三行。

include "postgres.h"

include "fmgr.h"

PG_MODULE_MAGIC;

extern "C" Datum add_ab(PG_FUNCTION_ARGS);

PG_FUNCTION_INFO_V1(add_ab);

Datum

add_ab(PG_FUNCTION_ARGS)

{

int32 arg_a = PG_GETARG_INT32(0);

int32 arg_b = PG_GETARG_INT32(1);

      PG_RETURN_INT32(arg_a + arg_b);

}

CMakeLists.txt

cmake_minimum_required (VERSION 2.8)

project (gs_plug)

set(CMAKE_CXX_FLAGS "-Wall -std=c++11 -Wall")

set(CMAKE_CXX_FLAGS_DEBUG "-g3")

set(CMAKE_CXX_FLAGS_RELEASE "-O2")

set(CMAKE_BUILD_TYPE Debug)

set(MOG_INCLUDE /opt/mogdb/app/include/postgresql/server)

set(MOG_LIBPATH /opt/mogdb/app/lib/postgresql/proc_srclib)

include_directories(${MOG_INCLUDE})

aux_source_directory(. DIR_SRCS)

add_library (${PROJECT_NAME} SHARED ${DIR_SRCS})

install(TARGETS ${PROJECT_NAME} DESTINATION ${MOG_LIBPATH})

要点 1：获取包含头文件的目录

[omm@vmpc funcs]$ pg_config --includedir

/opt/mogdb/app/include

所需头文件路径：pg_config --includedir/postgresql/server

要点 1：c 函数安装路径

[omm@vmpc funcs]$ pg_config --pkglibdir

/opt/mogdb/app/lib/postgresql

安装路径：pg_config --pkglibdir/proc_srclib/

编译 & 安装

[omm@vmpc funcs]$ mkdir build

[omm@vmpc funcs]$ cd build/

[omm@vmpc build]$ cmake ../

CMake Deprecation Warning at CMakeLists.txt:1 (cmake_minimum_required):

Compatibility with CMake < 2.8.12 will be removed from a future version of

CMake.

Update the VERSION argument value or use a ... suffix to tell

CMake that the project does not need compatibility with older versions.

-- The C compiler identification is GNU 4.8.5

-- The CXX compiler identification is GNU 4.8.5

-- Detecting C compiler ABI info

-- Detecting C compiler ABI info - done

-- Check for working C compiler: /bin/cc - skipped

-- Detecting C compile features

-- Detecting C compile features - done

-- Detecting CXX compiler ABI info

-- Detecting CXX compiler ABI info - done

-- Check for working CXX compiler: /bin/c++ - skipped

-- Detecting CXX compile features

-- Detecting CXX compile features - done

-- Configuring done

-- Generating done

-- Build files have been written to: /opt/mogdb/funcs/build

[omm@vmpc build]$ make

[ 50%] Building CXX object CMakeFiles/gs_plug.dir/testfunc.cpp.o

[100%] Linking CXX shared library libgs_plug.so

[100%] Built target gs_plug

[omm@vmpc build]$ make install

Consolidate compiler generated dependencies of target gs_plug

[100%] Built target gs_plug

Install the project...

-- Install configuration: "Debug"

-- Installing: /opt/mogdb/app/lib/proc_srclib/libgs_plug.so

依次执行如下命令

mkdir build

cd build

cmake ../

make

make install

确认安装

[omm@vmpc build]$ ll /opt/mogdb/app/lib/proc_srclib/libgs_plug.so

-rwxr-xr-x. 1 omm dbgrp 215696 Apr 2 00:17 /opt/mogdb/app/lib/proc_srclib/libgs_plug.so

验证

链接 mogdb

[omm@vmpc ~]$ pgcli -p 26000 -d postgres

Server: PostgreSQL 9.2.4

Version: 3.4.1

Home: http://pgcli.com

postgres>

创建 C FUNCTION

postgres> CREATE FUNCTION add_ab(a int ,b int ) RETURNS integer

AS 'testfunc.so', 'add_ab'

LANGUAGE C STRICT;

CREATE FUNCTION

Time: 0.039s

查看函数

调用函数

postgres> select add_ab(a := 4, b := 2);

+--------+

add_ab

6

+--------+

SELECT 1

Time: 0.033s

postgres>