本节以实现Oracle中的add_months函数为例介绍如何通过改造内核实现自定义系统函数.
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一、基础知识
在实现之前有必要先行介绍一些基础知识,包括Oid/函数注册等.
Oid
Oid即Object identifier,对象标识符,在PostgreSQL中,每个对象都一个Oid,系统表对象之间以Oid进行关联.
函数作为PostgreSQL中的一种对象,每个函数都存在Oid,通过查询pg_proc可获得相关信息:
postgres=# select oid,proname from pg_proc order by oid;
oid | proname
-------+----------------------------------------------
31 | byteaout
33 | charout
34 | namein
35 | nameout
38 | int2in
39 | int2out
40 | int2vectorin
41 | int2vectorout
42 | int4in
43 | int4out
44 | regprocin
45 | regprocout
46 | textin
47 | textout
48 | tidin
49 | tidout
50 | xidin
51 | xidout
52 | cidin
53 | cidout
54 | oidvectorin
55 | oidvectorout
56 | boollt
57 | boolgt
60 | booleq
--More--
函数注册
假设我们已经实现了一个自定义系统函数,比如add_months,PostgreSQL如何才能感知该函数的存在?答案是通过函数注册实现.
PostgreSQL在编译的时候,会用perl脚本根据预置的记录,生成src/backend/catalog/postgres.bki文件,该文件在initdb时被解析成一条条的SQL,插入到系统表中.因此自定义的系统函数,需要在通过initdb新建的数据库实例中才能被”感知”.
二、实现步骤
有了上面的基础知识,接下来我们step by step的实现add_months自定义函数.
1.获取函数Oid
PostgreSQL提供了unused_oids工具用于快速检索未使用的Oid,该文件位于src/include/catalog目录下
find -name unused_oids
./src/include/catalog/unused_oids
[root@localhost pg11]# ./src/include/catalog/unused_oids
2 - 9
3423 - 3436
3996
3998
4001 - 4013
4142 - 4199
4217 - 4565
4572 - 4999
5017 - 5027
5029 - 5999
6015 - 6099
6103
6105
6107 - 6109
6116
6122 - 9999
我们选择了Oid = 5100
2.注册函数
在文件pg_proc.dat中添加add_months函数
#src/include/catalog/pg_proc.dat
...
{ oid => '5100', descr => 'oracle-like add_months function',
proname => 'add_months', provariadic => '0',
proisstrict => 'f', prorettype => 'date', proargtypes => 'date int4',
prosrc => 'add_months'},
该文件中的条目对应结构体Form_pg_proc
/* ----------------
* pg_proc definition. cpp turns this into
* typedef struct FormData_pg_proc
* pg_proc定义
* ----------------
*/
CATALOG(pg_proc,1255,ProcedureRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(81,ProcedureRelation_Rowtype_Id) BKI_SCHEMA_MACRO
{
/* procedure name */
//过程名称
NameData proname;
/* OID of namespace containing this proc */
//系统OID
Oid pronamespace BKI_DEFAULT(PGNSP);
/* procedure owner */
//拥有者Owner
Oid proowner BKI_DEFAULT(PGUID);
/* OID of pg_language entry */
//实现语言调用接口,pg_language中的OID.
//默认为12-internal,其他选项包括13-c语言,14-sql,13275-plpgsql
Oid prolang BKI_DEFAULT(12);
/* estimated execution cost */
//估算的执行成本,默认为1
float4 procost BKI_DEFAULT(1);
/* estimated # of rows out (if proretset) */
//估算的结果行数,默认为0
float4 prorows BKI_DEFAULT(0);
/* element type of variadic array, or 0 */
//可变数组参数元素类型,默认为0
Oid provariadic BKI_DEFAULT(0) BKI_LOOKUP(pg_type);
/* transforms calls to it during planning */
//在计划期间的转换调用,默认为0
//可通过此列指定的函数来简化
regproc protransform BKI_DEFAULT(0) BKI_LOOKUP(pg_proc);
/* see PROKIND_ categories below */
//详见下面的PROKIND_XXX
char prokind BKI_DEFAULT(f);
/* security definer */
//安全定义器
bool prosecdef BKI_DEFAULT(f);
/* is it a leak-proof function? */
//弱认证函数?除了返回值,没有关系参数的信息被传播
bool proleakproof BKI_DEFAULT(f);
/* strict with respect to NULLs? */
//NULLs的处理(严格还是不严格)
bool proisstrict BKI_DEFAULT(t);
/* returns a set? */
//返回集合?默认为F
bool proretset BKI_DEFAULT(f);
/* see PROVOLATILE_ categories below */
//详见下面的PROVOLATILE_XXX
char provolatile BKI_DEFAULT(i);
/* see PROPARALLEL_ categories below */
//详见下面的PROPARALLEL_XXX
char proparallel BKI_DEFAULT(s);
/* number of arguments */
/* Note: need not be given in pg_proc.dat; genbki.pl will compute it */
//参数个数
//注意:不需要在pg_proc.dat中指定,genbki.pl会自动计算
int16 pronargs;
/* number of arguments with defaults */
//有默认值的参数个数
int16 pronargdefaults BKI_DEFAULT(0);
/* OID of result type */
//结果类型OID
Oid prorettype BKI_LOOKUP(pg_type);
/*
* variable-length fields start here, but we allow direct access to
* proargtypes
* 从这里开始为可变长字段,但我们运行直接访问原型类型
*/
/* parameter types (excludes OUT params) */
//参数类型(剔除了OUT参数)
//只包括输入参数（含INOUT和VARIADIC参数
oidvector proargtypes BKI_LOOKUP(pg_type);
#ifdef CATALOG_VARLEN
/* all param types (NULL if IN only) */
//所有参数类型(数组),包括所有参数（含OUT和INOUT参数）
//如都为IN类型,则为NULL
Oid proallargtypes[1] BKI_DEFAULT(_null_) BKI_LOOKUP(pg_type);
/* parameter modes (NULL if IN only) */
//参数模式数组(如都为IN参数,则为NULL)
// i表示IN参数 ， o表示OUT参数， b表示INOUT参数， v表示VARIADIC参数， t表示TABLE参数
char proargmodes[1] BKI_DEFAULT(_null_);
/* parameter names (NULL if no names) */
//参数名称数组(如无则为NULL)
//这里的下标对应着proallargtypes而不是proargtypes中的位置
text proargnames[1] BKI_DEFAULT(_null_);
/* list of expression trees for argument defaults (NULL if none) */
//参数默认值表达式树链表(如无则为NULL)
//对应proargtypes
pg_node_tree proargdefaults BKI_DEFAULT(_null_);
/* types for which to apply transforms */
//应用变换的类型
Oid protrftypes[1] BKI_DEFAULT(_null_);
/* procedure source text */
//过程实现文本(如为c,则可为函数名称)
text prosrc BKI_FORCE_NOT_NULL;
/* secondary procedure info (can be NULL) */
//第二个过程信息,即附加信息(可为NULL)
text probin BKI_DEFAULT(_null_);
/* procedure-local GUC settings */
//与过程相关的本地GUC设置
text proconfig[1] BKI_DEFAULT(_null_);
/* access permissions */
//访问权限
aclitem proacl[1] BKI_DEFAULT(_null_);
#endif
} FormData_pg_proc;
/* ----------------
* Form_pg_proc corresponds to a pointer to a tuple with
* the format of pg_proc relation.
* ----------------
*/
typedef FormData_pg_proc *Form_pg_proc;
#ifdef EXPOSE_TO_CLIENT_CODE
/*
* Symbolic values for prokind column
*/
#define PROKIND_FUNCTION 'f'
#define PROKIND_AGGREGATE 'a'
#define PROKIND_WINDOW 'w'
#define PROKIND_PROCEDURE 'p'
/*
* Symbolic values for provolatile column: these indicate whether the result
* of a function is dependent *only* on the values of its explicit arguments,
* or can change due to outside factors (such as parameter variables or
* table contents). NOTE: functions having side-effects, such as setval(),
* must be labeled volatile to ensure they will not get optimized away,
* even if the actual return value is not changeable.
*/
#define PROVOLATILE_IMMUTABLE 'i' /* never changes for given input */
#define PROVOLATILE_STABLE 's' /* does not change within a scan */
#define PROVOLATILE_VOLATILE 'v' /* can change even within a scan */
/*
* Symbolic values for proparallel column: these indicate whether a function
* can be safely be run in a parallel backend, during parallelism but
* necessarily in the master, or only in non-parallel mode.
*/
#define PROPARALLEL_SAFE 's' /* can run in worker or master */
#define PROPARALLEL_RESTRICTED 'r' /* can run in parallel master only */
#define PROPARALLEL_UNSAFE 'u' /* banned while in parallel mode */
/*
* Symbolic values for proargmodes column. Note that these must agree with
* the FunctionParameterMode enum in parsenodes.h; we declare them here to
* be accessible from either header.
*/
#define PROARGMODE_IN 'i'
#define PROARGMODE_OUT 'o'
#define PROARGMODE_INOUT 'b'
#define PROARGMODE_VARIADIC 'v'
#define PROARGMODE_TABLE 't'
#endif /* EXPOSE_TO_CLIENT_CODE */
通过perl脚本,PG会把该定义文件中的条目生成postgres.bki文件,查看Makefile文件(src/backend/catalog/Makefile)中的注释:
# bki-stamp records the last time we ran genbki.pl. We don't rely on
# the timestamps of the individual output files, because the Perl script
# won't update them if they didn't change (to avoid unnecessary recompiles).
# Technically, this should depend on Makefile.global which supplies
# $(MAJORVERSION); but then genbki.pl would need to be re-run after every
# configure run, even in distribution tarballs. So depending on configure.in
# instead is cheating a bit, but it will achieve the goal of updating the
# version number when it changes.
bki-stamp: genbki.pl Catalog.pm $(POSTGRES_BKI_SRCS) $(POSTGRES_BKI_DATA) $(top_srcdir)/configure.in
$(PERL) -I $(catalogdir) $< --set-version=$(MAJORVERSION) $(POSTGRES_BKI_SRCS)
touch $@
编译成功后,生成的src/backend/catalog/postgres.bki中包含了我们添加的条目(OID = 5100):
...
insert OID = 5028 ( satisfies_hash_partition 11 10 12 1 0 2276 0 f f f f f i s 4 0 16 "26 23 23 2276" _null_ "{i,i,i,v}" _null_ _null_ _null_ satisfies_hash_partition _null_ _null_ _null_ )
insert OID = 5100 ( add_months 11 10 12 1 0 0 0 f f f f f i s 2 0 1082 "1082 23" _null_ _null_ _null_ _null_ _null_ add_months _null_ _null_ _null_ )
close pg_proc
...
3.实现功能
在src/backend/utils/adt/date.c文件的最后添加逻辑实现.
该实现使用了Github开源项目orafce中的实现(
感谢开源!
)
Datum
add_months(PG_FUNCTION_ARGS)
{
DateADT day = PG_GETARG_DATEADT(0);
int n = PG_GETARG_INT32(1);
int y, m, d;
int days;
DateADT result;
div_t v;
bool last_day;
j2date(day + POSTGRES_EPOCH_JDATE, &y, &m, &d);
last_day = (d == days_of_month(y, m));
v = div(y * 12 + m - 1 + n, 12);
y = v.quot;
if (y < 0)
y += 1; /* offset because of year 0 */
m = v.rem + 1;
days = days_of_month(y, m);
if (last_day || d > days)
d = days;
result = date2j(y, m, d) - POSTGRES_EPOCH_JDATE;
PG_RETURN_DATEADT (result);
}
int
days_of_month(int y, int m)
{
int month_days[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
int days;
if (m < 0 || 12 < m)
ereport(ERROR,
(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
errmsg("date out of range")));
days = month_days[m - 1];
if (m == 2 && (y % 400 == 0 || (y % 4 == 0 && y % 100 != 0)))
days += 1; /* February 29 in leap year */
return days;
}
在头文件src/include/utils/date.h中添加函数声明
extern Datum add_months(PG_FUNCTION_ARGS);
4.编译安装
make clean
make
make install
5.初始化数据库
initdb -D /data/pgsql/tmpdb
pg_ctl start -D /data/pgsql/tmpdb
6.检查验证
postgres=# select add_months(current_date,12);
add_months
------------
2020-04-28
(1 row)
DONE!
三、参考资料
Oid
orafce
