本节简单介绍了如何实现扩展函数.
主要内容翻译自 PostgreSQL: Simple C extension Development for a Novice User (and Performance Advantages)

一、实现步骤

假设我们已在CentOs7.x上使用源码安装了PG,当前用户为PG实例的owner(pg12),已配置好环境变量,可以运行pg_config命令

[pg12@localhost demo_plus]$ whoami
pg12
[pg12@localhost ~]$ cat .bashrc
# .bashrc
# Source global definitions
if [ -f /etc/bashrc ]; then. /etc/bashrc
fi
# Uncomment the following line if you don't like systemctl's auto-paging feature:
# export SYSTEMD_PAGER=
# User specific aliases and functions
export PATH=/appdb/xdb/pg12beta1/bin:$PATH
export PGDATA=/data/pgsql/pg12db1
[pg12@localhost ~]$ pg_config --pgxs
/appdb/xdb/pg12beta1/lib/postgresql/pgxs/src/makefiles/pgxs.mk

创建源码目录

[pg12@localhost source]$ mkdir -p extension/demo_plus
[pg12@localhost source]$ cd extension/demo_plus/

使用C作为extension的实现语言,参照PG extension Makefile文件格式编写Makefile文件

[pg12@localhost demo_plus]$ cat Makefile
MODULES = demo_plus
EXTENSION = demo_plus
DATA = demo_plus--0.0.1.sql
PG_CONFIG = pg_config
PGXS := $(shell $(PG_CONFIG) --pgxs)
include $(PGXS)

MODULES:扩展模块,待Build的Module
EXTENSION:扩展名称,可与Modules不同
DATA:安装脚本
0.0.1:版本

下面创建extension control文件

[pg12@localhost demo_plus]$ cat demo_plus.control
comment = 'Simple number add function'
default_version = '0.0.1'
relocatable = true
module_pathname = '$libdir/demo_plus'

comment:注释
default_version:默认版本
relocatable:是否重新加载
module_pathname:所在路径

接下来是实现文件demo_plus.c

[pg12@localhost demo_plus]$ cat demo_plus.c
#include "postgres.h"
#include "fmgr.h"
PG_MODULE_MAGIC;
PG_FUNCTION_INFO_V1(demo_plus);
Datum
demo_plus(PG_FUNCTION_ARGS)
{
int32 arg1 = PG_GETARG_INT32(0);
int32 arg2 = PG_GETARG_INT32(1);
PG_RETURN_INT32(arg1 + arg2);
}

逻辑很简单,输入两个数,返回两个数相加的结果.make编译

[pg12@localhost demo_plus]$ ls -l
total 12
-rw-rw-r--. 1 pg12 pg12 220 Aug  8 11:21 demo_plus.c
-rw-rw-r--. 1 pg12 pg12 123 Aug  8 11:18 demo_plus.control
-rw-rw-r--. 1 pg12 pg12 146 Aug  8 11:18 Makefile
[pg12@localhost demo_plus]$ make
gcc -std=gnu99 -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -g -O0 -DOPTIMIZER_DEBUG -g3 -gdwarf-2 -fPIC -I. -I./ -I/appdb/xdb/pg12beta1/include/postgresql/server -I/appdb/xdb/pg12beta1/include/postgresql/internal  -D_GNU_SOURCE -I/usr/include/libxml2   -c -o demo_plus.o demo_plus.c -MMD -MP -MF .deps/demo_plus.Po
gcc -std=gnu99 -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -g -O0 -DOPTIMIZER_DEBUG -g3 -gdwarf-2 -fPIC demo_plus.o -L/appdb/xdb/pg12beta1/lib   -Wl,--as-needed -Wl,-rpath,'/appdb/xdb/pg12beta1/lib',--enable-new-dtags  -shared -o demo_plus.so

最后一步,创建sql文件用于生成函数

[pg12@localhost demo_plus]$ cat demo_plus-0.0.1.sql
CREATE OR REPLACE FUNCTION
demofunc1(int,int) RETURNS int AS 'MODULE_PATHNAME','demo_plus'
LANGUAGE C STRICT;
[pg12@localhost demo_plus]$

执行make install安装

[pg12@localhost demo_plus]$ sudo make install
make -C ../../src/backend generated-headers
make[1]: Entering directory `/data/source/postgresql-12beta1/src/backend'
make -C catalog distprep generated-header-symlinks
make[2]: Entering directory `/data/source/postgresql-12beta1/src/backend/catalog'
make[2]: Nothing to be done for `distprep'.
make[2]: Nothing to be done for `generated-header-symlinks'.
make[2]: Leaving directory `/data/source/postgresql-12beta1/src/backend/catalog'
make -C utils distprep generated-header-symlinks
make[2]: Entering directory `/data/source/postgresql-12beta1/src/backend/utils'
make[2]: Nothing to be done for `distprep'.
make[2]: Nothing to be done for `generated-header-symlinks'.
make[2]: Leaving directory `/data/source/postgresql-12beta1/src/backend/utils'
make[1]: Leaving directory `/data/source/postgresql-12beta1/src/backend'
/usr/bin/mkdir -p '/appdb/xdb/pg12beta1/share/postgresql/extension'
/usr/bin/mkdir -p '/appdb/xdb/pg12beta1/share/postgresql/extension'
/usr/bin/mkdir -p '/appdb/xdb/pg12beta1/lib/postgresql'
/usr/bin/install -c -m 644 ./demo_plus.control '/appdb/xdb/pg12beta1/share/postgresql/extension/'
/usr/bin/install -c -m 644 ./demo_plus--0.0.1.sql  '/appdb/xdb/pg12beta1/share/postgresql/extension/'
/usr/bin/install -c -m 755  demo_plus.so '/appdb/xdb/pg12beta1/lib/postgresql/'

创建extension,执行函数

testdb=# create extension demo_plus;
CREATE EXTENSION

PL/pgSQL vs C Extension
C Extension的性能接近于原生内置函数(+),而PL/pgSQL的执行时间则是原生的2倍+

CREATE FUNCTION plpgsql_demo_plus(a integer, b integer)RETURNS integer
as $$
BEGINreturn a+b;
END;
$$ LANGUAGE plpgsql;
[xdb@localhost ~]$ time psql -c "select plpgsql_demo_plus(floor(random() * (100-1+1) + 1)::int,x) from generate_series(1,1000000) as x" -p 5433 -d testdb > out.txt
real    0m3.753s
user    0m0.924s
sys    0m0.658s
[xdb@localhost ~]$ time psql -c "select demo_plus(floor(random() * (100-1+1) + 1)::int,x) from generate_series(1,1000000) as x" -p 5433 -d testdb > out.txt
real    0m1.685s
user    0m1.005s
sys    0m0.093s
[xdb@localhost ~]$ time psql -c "select floor(random() * (100-1+1) + 1)::int+x from generate_series(1,1000000) as x" -p 5433 -d testdb > out.txt
real    0m1.666s
user    0m0.992s
sys    0m0.067s

二、配置文件说明

Makefile
MODULES
list of shared-library objects to be built from source files with same stem (do not include library suffixes in this list)
MODULE big
a shared library to build from multiple source files (list object files in OBJS)
PROGRAM
an executable program to build (list object files in OBJS)
EXTENSION
extension name(s); for each name you must provide an extension.control file, which will be installed into prefix/share/extension
MODULEDIR
subdirectory of prefix/share into which DATA and DOCS files should be installed (if not set, default is extension if EXTENSION is set, or contrib if not)
DATA
random files to install into prefix/share/$MODULEDIR
DATA_built
random files to install into prefix/share/$MODULEDIR, which need to be built first
DATA_TSEARCH
random files to install under prefix/share/tsearch_data
DOCS
random files to install under prefix/doc/$MODULEDIR
HEADERS
HEADERS_built
Files to (optionally build and) install under prefix/include/server/$MODULEDIR/$MODULE_big.
Unlike DATA_built, files in HEADERS_built are not removed by the clean target; if you want them removed, also add them to EXTRA_CLEAN or add your own rules to do it.
HEADERS$MODULE
HEADERS built $MODULE
Files to install (after building if specified) under prefix/include/server/$MODULEDIR/$MODULE, where $MODULE must be a module name used in MODULES or MODULE big.
Unlike DATA_built, files in HEADERS_built$MODULE are not removed by the clean target; if you want them removed, also add them to EXTRA CLEAN or add your own rules to do it.
It is legal to use both variables for the same module, or any combination, unless you have two module names in the MODULES list that differ only by the presence of a prefix built, which would cause ambiguity. In that (hopefully unlikely) case, you should use only the HEADERS built $MODULE variables.
SCRIPTS
script files (not binaries) to install into prefix/bin
SCRIPTS_built
script files (not binaries) to install into prefix/bin, which need to be built first
REGRESS
list of regression test cases (without suffix), see below
REGRESS_OPTS
additional switches to pass to pg_regress
ISOLATION
list of isolation test cases, see below for more details
ISOLATION_OPTS
additional switches to pass to pg_isolation_regress
TAP_TESTS
switch defining if TAP tests need to be run, see below
NO_INSTALLCHECK
don’t define an installcheck target, useful e.g. if tests require special configuration, or don’t use pg_regress
EXTRA_CLEAN
extra files to remove in make clean
PG_CPPFLAGS
will be prepended to CPPFLAGS
PG_CFLAGS
will be appended to CFLAGS
PG_CXXFLAGS
will be appended to CXXFLAGS
PG_LDFLAGS
will be prepended to LDFLAGS
PG_LIBS
will be added to PROGRAM link line
SHLIB_LINK
will be added to MODULE_big link line
PG_CONFIG
path to pg_config program for the PostgreSQL installation to build against (typically just pg_config to use the first one in your PATH)

control file
A control file can set the following parameters:
directory (string)
The directory containing the extension’s SQL script file(s). Unless an absolute path is given, the name is relative to the installation’s SHAREDIR directory. The default behavior is equivalent to specifying directory = ‘extension’.
default_version (string)
The default version of the extension (the one that will be installed if no version is specified in CREATE EXTENSION). Although this can be omitted, that will result in CREATE EXTENSION failing if no VERSION option appears, so you generally don’t want to do that.
comment (string)
A comment (any string) about the extension. The comment is applied when initially creating an extension, but not during extension updates (since that might override user-added comments). Alternatively, the extension’s comment can be set by writing a COMMENT command in the script file.
encoding (string)
The character set encoding used by the script file(s). This should be specified if the script files contain any non-ASCII characters. Otherwise the files will be assumed to be in the database encoding.
module_pathname (string)
The value of this parameter will be substituted for each occurrence of MODULE_PATHNAME in the script file(s). If it is not set, no substitution is made. Typically, this is set to $libdir/shared_library_name and then MODULE_PATHNAME is used in CREATE FUNCTION commands for C-language functions, so that the script files do not need to hard-wire the name of the shared library.
requires (string)
A list of names of extensions that this extension depends on, for example requires = ‘foo, bar’. Those extensions must be installed before this one can be installed.
superuser (boolean)
If this parameter is true (which is the default), only superusers can create the extension or update it to a new version. If it is set to false, just the privileges required to execute the commands in the installation or update script are required.
relocatable (boolean)
An extension is relocatable if it is possible to move its contained objects into a different schema after initial creation of the extension. The default is false, i.e. the extension is not relocatable. See Section 37.17.3 for more information.
schema (string)
This parameter can only be set for non-relocatable extensions. It forces the extension to be loaded into exactly the named schema and not any other. The schema parameter is consulted only when initially creating an extension, not during extension updates. See Section 37.17.3 for more information.

三、参考资料

PostgreSQL: Simple C extension Development for a Novice User (and Performance Advantages)
Packaging Related Objects into an Extension
Extension Building Infrastructure