目标：从 RRULE 字符串（即FREQ=WEEKLY;INTERVAL=2;COUNT=8;WKST=SU;BYDAY=TU,TH）和起始时间戳生成时间戳列表，每个时间戳代表一个事件发生。由于这些时间会随用户的心血来潮而改变，因此需要 postgresql，因为 (1) 它具有严格的业务逻辑质量和 (2) 触发器（值更改时自动更新行）
替代解决方案：
我最终使用了 plpythonu（postgresql 的 python 语言）。dateutil库有一个很棒的规则解析器。
mydatabase=# CREATE FUNCTION parse_occurrences(rule text, start timestamp) RETURNS timestamp[] AS
mydatabase-# 'from dateutil.rrule import *
mydatabase'# from dateutil.parser import *
mydatabase'# import datetime
mydatabase'# dates = list(rrulestr(rule, dtstart=parse(start)))
mydatabase'# return [str(a)[0:10] for a in dates]'
mydatabase-# LANGUAGE plpythonu;
CREATE FUNCTION
mydatabase=# SELECT parse_occurrences('FREQ=WEEKLY;INTERVAL=2;COUNT=8;WKST=SU;BYDAY=TU,TH'::text, now()::timestamp);
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
{"2013-02-14 00:00:00","2013-02-26 00:00:00","2013-02-28 00:00:00","2013-03-12 00:00:00","2013-03-14 00:00:00","2013-03-26 00:00:00","2013-03-28 00:00:00","2013-04-09 00:00:00"}
（原始）努力：将C-library libical与Postgresql C-Extensions连接起来。这需要专门的 C 程序来执行以下操作：(1) 将 postgresql 数据类型转换为 C 数据类型，(2) 执行所有必要的 C 库函数，以及 (3) 使用头文件以 postgresql 格式返回数据“ postgres.h”。
连接器文件：ical_recur.c
#include "postgres.h"
#include "icalrecur.h"
#include <time.h> /* for time() */
#include "fmgr.h"
#ifdef PG_MODULE_MAGIC
PG_MODULE_MAGIC;
#endif
PG_FUNCTION_INFO_V1(get_occurrences);
Datum
get_occurrences(PG_FUNCTION_ARGS)
{
//char* rule; /* rule string */
time_t start; /* start time */
int count;
char *rrule;
// *rule = PG_GETARG_CHAR(0);
start = (time_t) PG_GETARG_INT32(1);
count = (int) PG_GETARG_INT32(2);
*rrule = PG_GETARG_CHAR(0);
time_t *result[count]; /* output array */
icalrecur_expand_recurrence(rrule, start, count, *result);
PG_RETURN_INT32(*result);
}
准备连接器文件：
步骤 1：编译到目标文件，创建共享对象，复制到 postgresql 查找 C-extensions 的位置
sudo gcc -I/usr/local/libical/lib -lical -I/usr/include/postgresql/9.2/server -fpic -c ical_recur.c
sudo gcc -shared -L/usr/local/libical/lib -lical -o ical_recur.so ical_recur.o
sudo cp ical_recur.so /usr/lib/postgresql/9.2/lib/
步骤 2：添加 C 找到的 libical lib 文件夹并重新加载配置
sudo echo "/usr/local/libical/lib" >> /etc/ld.so.conf.d/libc.conf
sudo ldconfig
测试连接器文件：
第 1 步：加载 psql 并创建函数
psql
mydatabase=# CREATE FUNCTION get_occurrences(text, integer, integer) RETURNS int[]
mydatabase=- AS '$libdir/ical_recur', 'get_occurrences'
mydatabase=- LANGUAGE C STRICT;
CREATE FUNCTION
mydatabase=#
当前的障碍：
C 函数使 postgresql 服务器崩溃。
psql (9.2.3)
Type "help" for help.
mydatabase=# SELECT get_occurrences('FREQ=WEEKLY;INTERVAL=2;COUNT=8;WKST=SU;BYDAY=TU,TH', now()::timestamp, 5);
The connection to the server was lost. Attempting reset: Failed.
!>
日志...
2013-02-11 22:03:33 UTC LOG: server process (PID 22733) was terminated by signal 11: Segmentation fault
2013-02-11 22:03:33 UTC DETAIL: Failed process was running: SELECT get_occurrences('FREQ=WEEKLY;INTERVAL=2;COUNT=8;WKST=SU;BYDAY=TU,TH', now()::timestamp, 5);
2013-02-11 22:03:33 UTC LOG: terminating any other active server processes
2013-02-11 22:03:33 UTC WARNING: terminating connection because of crash of another server process
2013-02-11 22:03:33 UTC DETAIL: The postmaster has commanded this server process to roll back the current transaction and exit, because another server process exited abnormally and possibly corrupted shared memory.
2013-02-11 22:03:33 UTC HINT: In a moment you should be able to reconnect to the database and repeat your command.
2013-02-11 22:03:33 UTC LOG: all server processes terminated; reinitializing
2013-02-11 22:03:33 UTC FATAL: the database system is in recovery mode
2013-02-11 22:03:33 UTC LOG: database system was interrupted; last known up at 2013-02-11 21:47:26 UTC
2013-02-11 22:03:33 UTC LOG: database system was not properly shut down; automatic recovery in progress
2013-02-11 22:03:33 UTC LOG: redo starts at 0/1903A0C
2013-02-11 22:03:33 UTC LOG: record with zero length at 0/190E1E0
2013-02-11 22:03:33 UTC LOG: redo done at 0/190E1B8
2013-02-11 22:03:33 UTC LOG: last completed transaction was at log time 2013-02-11 22:03:29.641161+00
2013-02-11 22:03:33 UTC LOG: database system is ready to accept connections
2013-02-11 22:03:33 UTC LOG: autovacuum launcher started
更新：
我已经更新了方法来解决一些建议。
#include "postgres.h"
#include "icalrecur.h"
#include <time.h> /* for time() */
#include "fmgr.h"
#ifdef PG_MODULE_MAGIC
PG_MODULE_MAGIC;
#endif
PG_FUNCTION_INFO_V1(get_occurrences);
Datum
get_occurrences(PG_FUNCTION_ARGS)
{
time_t start = (time_t) PG_GETARG_INT32(1); /* convert int to time_t */
int count = PG_GETARG_INT32(2);
char rrule = PG_GETARG_CHAR(0);
char *_rrule = &rrule; /* icalrecur wants a pointer to the rrule */
time_t result[count]; /* instantiate the output array */
int success = icalrecur_expand_recurrence(_rrule, start, count, result);
/* convert time_t values to int */
int *output = malloc(sizeof(result));
int i;
for(i = 0; i < (int) (sizeof(result) / sizeof(result[0]) - 1); i++){
output[i] = (int) result[i];
}
if(success != 1){
PG_RETURN_INT32(0);
} else {
PG_RETURN_INT32(output);
}
}
建筑与..
sudo gcc -Wall -Wextra -l/usr/local/libical/lib/ical -I/usr/local/libical/include/libical -I/usr/include/postgresql/9.2/server -fpic -c ical_recur.c
sudo gcc -Wall -shared -static -L/usr/local/libical/lib -lical -o ical_recur.so ical_recur.o
sudo cp libical.so /usr/lib/postgresql/9.2/lib/
进入数据库并执行..
mydb=# CREATE FUNCTION get_occurrences(text, integer, integer) RETURNS int[]
AS '$libdir/ical_recur', 'get_occurrences'
LANGUAGE C STRICT;
CREATE FUNCTION
mydb=# SELECT get_occurrences('FREQ=WEEKLY;INTERVAL=2;COUNT=8;WKST=SU;BYDAY=TU,TH', 1360690024, 5);
The connection to the server was lost. Attempting reset: Failed.
!> \q
相同的日志输出。文档说明了参数：
int icalrecur_expand_recurrence(char * rule, time_t start, int count, time_t * array)
问题：我们怎样才能让它在没有 postgres 崩溃的情况下工作？