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<div class="width6 last">
<div class="section_header">Frequently Asked Questions (FAQ)</div>
<ul>
<li><a href="#dst">How does Taskforest deal with Daylight Saving Time?</a></li>
<li><a href="#midnight">How can I run jobs overnight?</a></li>
<li><a href="#long">Does TaskForest support jobs that run for longer than 24 hours?</a></li>
<li><a href="#tz">What time zones are available?</a></li>
<li><a href="#tokens">Can I prevent too many jobs from running simultaneously?</a></li>
</ul>
<div class="new_section_header"><a name="dst">How does Taskforest deal with Daylight Saving Time?</a></div>
<p>
For time zones that observe Daylight Saving Time, on the day that DST
starts (in Spring) the day has only 23 hours. On the day that DST
ends the day has 25 hours. If you run an hourly job on those days,
the job will run either 23 or 25 times. If you prefer, you can have
your Family file use a timezone that does not observe DST - like GMT,
for instance.
</p>
<div class="new_section_header"><a name="midnight">How can I run jobs overnight?</a></div>
<p>
Having a midnight point gives us a convenient time interval within
which a run of a job is considered valid. For example, with the
system as it is now, saying "job J1 has run" means that it has run
*today*. If J2 depends on J1, we only have to look for successful
runs of J1 today.
</p>
<p>
If we don't have a known time interval, then we have to resolve the
problem that occurs when jobs run for longer than 24 hours. Let's
start with a simple example first. Assume that our Family file looks
like this:
</p>
<div class="code"><pre><code>
+----------------------------------------------------------------
|start=>'00:00',tz=>'America/Chicago',days=>'Mon,Tue,Wed,Thu,Fri'
| | J1( start=>22:00 ) | J2()
+----------------------------------------------------------------
</code></pre></div>
<div class="example_name">Example 1: J1's run time is 5 hours. This is what happens today</div>
<div class="code"><pre><code>
(Chicago)
Day Time Action(s)
Mon 00:00
01:00
02:00
03:00
04:00
05:00
06:00
07:00
08:00
09:00
11:00
12:00
13:00
14:00
15:00
16:00
17:00
18:00
19:00
20:00
21:00
22:00 J1 Starts
23:00 |
Tue 00:00 |
01:00 |
02:00 v
03:00 J1 Ends
04:00
05:00
06:00
07:00
08:00
09:00
11:00
12:00
13:00
14:00
15:00
16:00
17:00
18:00
19:00
20:00
21:00
22:00 J1 Starts
23:00 |
Wed 00:00 |
01:00 |
02:00 v
03:00 J1 Ends
04:00
</code></pre></div>
<p>
So you can see that J2 never gets a chance to run! At 03:00 on Tuesday,
the system checks to see if J1 has run for that day, and it hasn't. So J2
can't run for that day.
</p>
<p>
Now, I could remedy this particular case with the following technique (or
hack):
</p>
<div class="example_name">Example 2: J1's run time is 5 hours. J2's run time is 1 hour.</div>
<p>
Change the Family File to say:
</p>
<div class="code"><pre><code>
+----------------------------------------------------------------
| # changed the start time, time zone and days of week
|start => '00:00', tz => <em>'GMT'</em>, days => <em>'Tue,Wed,Thu,Fri,Sat'</em>
|
| J1( <em>start=>03:00</em> )
| J2()
+----------------------------------------------------------------
</code></pre></div>
<p>
What this does is *shift* the entire Family so that all jobs in it run
on the same day in the time zone specified. If you use cron to invoke
TaskForest, the crontab entry that invokes taskforest does not need to
be changed. That can stay the same. Now, this is what happens:
</p>
<div class="code"><pre><code>
(Chicago) (GMT)
Day Time Day Time Action(s)
Mon 00:00 Mon 05:00
01:00 06:00
02:00 07:00
03:00 08:00
04:00 09:00
05:00 11:00
06:00 12:00
07:00 13:00
08:00 14:00
09:00 15:00
11:00 16:00
12:00 17:00
13:00 18:00
14:00 19:00
15:00 20:00
16:00 21:00
17:00 22:00
18:00 23:00
19:00 Tue 00:00
20:00 01:00
21:00 02:00
22:00 03:00 J1 Starts
23:00 04:00 |
Tue 00:00 05:00 |
01:00 06:00 |
02:00 07:00 v
03:00 08:00 J1 Ends, J2 Starts
04:00 09:00 J2 Ends
05:00 11:00
06:00 12:00
07:00 13:00
08:00 14:00
09:00 15:00
11:00 16:00
12:00 17:00
13:00 18:00
14:00 19:00
15:00 20:00
16:00 21:00
17:00 22:00
18:00 23:00
19:00 Wed 00:00
20:00 01:00
21:00 02:00
22:00 03:00 J1 Starts
23:00 04:00 |
Wed 00:00 05:00 |
01:00 06:00 |
02:00 07:00 v
03:00 08:00 J1 Ends, J2 Starts
04:00 09:00 J2 Ends
05:00 10:00
</code></pre></div>
<p>
Shifting the start/end of the days by changing the timezones has fixed
this problem. J1 still starts at 22:00 Chicago time, and J2 will
still run if J1 runs successfully.
</p>
<p>
If the jobs in your Family files run in less than 24 hours, you
can use this method now.
</p>
<p>
However, this is not a universal solution. What happens if J1's run time
is 26 hours? Even with the family as shown in Example 2, J1 ends the day
after it started. This means that J2 will never run, no matter what we set
the timezone to be. This is because no matter what day it is, <em>today's</em>
run of J1 will never have completed that day.
</p>
<p>
So the current version of taskforest does not support Family files whose
jobs run for more than 24 hours from the start of the first job to the end
of the last job, even if each individual job runs for less than 24 hours.
</p>
<div class="example_name">Example 3: J1 runs for 25 hours</div>
<div class="code"><pre><code>
(Chicago) (GMT)
Day Time Day Time Action(s)
Mon 00:00 Mon 05:00
01:00 06:00
02:00 07:00
03:00 08:00
04:00 09:00
05:00 11:00
06:00 12:00
07:00 13:00
08:00 14:00
09:00 15:00
11:00 16:00
12:00 17:00
13:00 18:00
14:00 19:00
15:00 20:00
16:00 21:00
17:00 22:00
18:00 23:00
19:00 Tue 00:00
20:00 01:00
21:00 02:00
22:00 03:00 J1 Starts
23:00 04:00 |
Tue 00:00 05:00 |
01:00 06:00 |
02:00 07:00 |
03:00 08:00 |
04:00 09:00 |
05:00 11:00 |
06:00 12:00 |
07:00 13:00 |
08:00 14:00 |
09:00 15:00 |
11:00 16:00 |
12:00 17:00 |
13:00 18:00 |
14:00 19:00 |
15:00 20:00 |
16:00 21:00 |
17:00 22:00 |
18:00 23:00 |
19:00 Wed 00:00 |
20:00 01:00 |
21:00 02:00 |
22:00 03:00 | J1 Starts
23:00 04:00 v |
Wed 00:00 05:00 J1 Ends |
01:00 06:00 |
02:00 07:00 |
03:00 08:00 |
04:00 09:00 |
05:00 10:00 |
</code></pre></div>
<p>
The other thing we're seeing here is that now we have 2 instances of J1
running simultaneously (for 2 hours), even though that is not the intent
of the Family file. This could be a major problem. J2 never runs.
</p>
<p>
I can't think of a foolproof way to resolve this.
</p>
<p>
If we implement rules that require a family to 'complete' all of the
previous day's jobs until it can run no more - because all jobs have
completed successfully. I don't know if this is a satisfactory approach
or not. This means that J1's start times will be as follows:
</p>
<div class="code"><pre><code>
Mon: 22:00
Wed: 00:00
</code></pre></div>
<p>
On Tuesday we don't run the Family, because Monday's run hasn't
completed. That's fine. But what about Wednesday? With this
definition, Wednesday will never run as well because Tuesday's run
never completed (there wasn't a run on Tuesday). So the system has to
be smart about that and realize that. And that's fine, until you
change the family on Tuesday to run a new job J3 after J2. Then, the
system needs to know on Wednesday not to wait for look for a
successful run of J3 for Monday's run (because J3 didn't exist on
Monday). Which means that the system needs to know your change
control history. Which is a whole other problem.
</p>
<div class="new_section_header"><a name="long">Does TaskForest support jobs that run for longer than 24 hours?</a></div>
<p>
No. For a detailed explanation, please see <a href="#midnight">the
answer to the previous FAQ</a>.
</p>
<div class="new_section_header"><a name="tz">What time zones are available?</a></div>
<p>
To see a list of all time zones you may use, you can read the perldoc
for <a href="http://search.cpan.org/dist/DateTime-TimeZone/lib/DateTime/TimeZone/Catalog.pm">DateTime::TimeZone::Catalog</a>.
</p>
<div class="new_section_header"><a name="tokens">Can I prevent too many jobs from running simultaneously?</a></div>
<p>
Yes. You can use <a href="/docs/tokens.html">tokens</a> to limit how
many jobs of a class may run simultaneously. If these jobs all use
the same token, you can set the cardinality of the token to the upper
limit on the number of jobs that may run simultaneously.
</p>
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