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)](https://www.percona.com/blog/2019/07/31/postgresql-simple-c-extension-development-for-a-novice-user/) ### 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 $$ BEGIN return a+b; END; $$ 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)](https://www.percona.com/blog/2019/07/31/postgresql-simple-c-extension-development-for-a-novice-user/) [Packaging Related Objects into an Extension](https://www.postgresql.org/docs/12/extend-extensions.html) [Extension Building Infrastructure](https://www.postgresql.org/docs/12/extend-pgxs.html)