-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Dave Page
Sent: 02 March 2005 20:25
To: [email protected]
Subject: [pgadmin-hackers] RFC: pgAgent Scheduler Design
<snip>
The basic design that I'm leaning towards is as follows, which each
schedule being represented in one row in a table.
Y'know, having thought about all that for a few days, I'm simply not happy with it - it's all too messy and inconsistent :-(.
So, thought #2 - follow a modified cron-style design:
Control -------
jscstart timestamptz -- date/time the schedule may start at. jscend timestamptz -- date/time the schedule will end at. jscenabled bool -- is the schedule active?
Note the lack of run counting in this design. This is primarily because missed runs (caused by system downtime for example) would be extremely difficult to count, potentially leading to errors calculating the schedule end. In addition, an end date would almost certainly give most people the flexibility they require.
Schedule --------
jscminutes bool[60] -- 0,1,2,3...59 jschours bool[24] -- 0,1,2,3...23 jscweekdays bool[7] -- mon,tue,wed...sun jscmonthdays bool[32] -- 0,1,2,3...31,last jscmonths bool[12] -- jan,feb,mar...dec
In this scheme, the elements of the arrays represent the possible values for each part of the schedule - for example, jscweekdays[] represents mon, tue, wed, thur, fri, sat, sun. If an array contains 'f' for all values, it is considered to be the cron * equivalent. jscmonthdays also includes an additional element to represent the last day of the month, regardless of it's actual number, per Andreas' suggestion.
As per cron, a simple algorithm would determine if a schedule should fire:
If ((jscminutes[datetime.minute] || jscminutes.IsAllFalse()) && (jschours[datetime.hour] || jschours.IsAllFalse()) && (jscweekdays[datetime.weekday] || jscweekdays.IsAllFalse()) && (jscmonthdays[datetime.monthday] || jscmonthdays.IsAllFalse() || (datetime.lastdayofmonth && jscmonthdays[32])) && (jscmonths[datetime.month] || jscmonths.IsAllFalse())) { FireSchedule(); }
(I think that's about right - it's been a long day :-) )
Sorry, this won't work.
It is mandatory that a "next run" schedule is calculated after a job has run, and FireSchedule will run when nextRun is >= current_timestamp.
Imagine two jobs scheduled for the very same minute, and only one pgAgent running. It will run the first job, which will run for lets say 2 minutes. After that, the fire time for the second job is not due any more, so it will run somewhat later, if ever.
That's what pga_next_schedule is good for. You'll have quite a hard time to calulate it from your way of storing schedules, I'm afraid... It's somewhat the difference between cron and anacron.
Regards, Andreas
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