15.11. Cylc 6 Migration Reference

Cylc 6 introduced new date-time-related syntax for the suite.rc file. In some places, this is quite radically different from the earlier syntax.

15.11.1. Timeouts and Delays

Timeouts and delays such as [cylc][[events]]timeout or [runtime][[my_task]][[[job]]]execution retry delays were written in a purely numeric form before cylc 6, in seconds, minutes (most common), or hours, depending on the setting.

They are now written in an ISO 8601 duration form, which has the benefit that the units are user-selectable (use 1 day instead of 1440 minutes) and explicit.

Nearly all timeouts and delays in cylc were in minutes, except for:

[runtime][[my_task]][[[suite state polling]]]interval
[runtime][[my_task]][[[simulation mode]]]run time range

which were in seconds, and

[scheduling]runahead limit

which was in hours (this is a special case discussed below in Runahead Limit).

See Table X.

Table 3 Timeout/Delay Syntax Change Examples
Setting Pre-Cylc-6 Cylc-6+
[cylc][[events]]timeout 180 PT3H
[runtime][[my_task]][[[job]]]execution retry delays 2*30, 360, 1440 2*PT30M, PT6H, P1D
[runtime][[my_task]][[[suite state polling]]]interval 2 PT2S

15.11.2. Runahead Limit

See [scheduling] -> runahead limit.

The [scheduling]runahead limit setting was written as a number of hours in pre-cylc-6 suites. This is now in ISO 8601 format for date-time cycling suites, so [scheduling]runahead limit=36 would be written [scheduling]runahead limit=PT36H.

There is a new preferred alternative to runahead limit, [scheduling]max active cycle points. This allows the user to configure how many cycle points can run at once (default 3). See [scheduling] -> max active cycle points.

15.11.3. Cycle Time/Cycle Point

See [scheduling] -> initial cycle point.

The following suite.rc settings have changed name (Table X):

Table 4 Cycle Point Renaming
Pre-Cylc-6 Cylc-6+
[scheduling]initial cycle time [scheduling]initial cycle point
[scheduling]final cycle time [scheduling]final cycle point
[visualization]initial cycle time [visualization]initial cycle point
[visualization]final cycle time [visualization]final cycle point

This change is to reflect the fact that cycling in cylc 6+ can now be over e.g. integers instead of being purely based on date-time.

Date-times written in initial cycle time and final cycle time were in a cylc-specific 10-digit (or less) CCYYMMDDhh format, such as 2014021400 for 00:00 on the 14th of February 2014.

Date-times are now required to be ISO 8601 compatible. This can be achieved easily enough by inserting a T between the day and the hour digits.

Table 5 Cycle Point Syntax Example
Setting Pre-Cylc-6 Cylc-6+
[scheduling]initial cycle time 2014021400 20140214T00

15.11.4. Cycling

Special start-up and cold-start tasks have been removed from cylc 6. Instead, use the initial/run-once notation as detailed in Initial Non-Repeating (R1) Tasks and Advanced Starting Up.

Repeating asynchronous tasks have also been removed because non date-time workflows can now be handled more easily with integer cycling. See for instance the satellite data processing example documented in Integer Cycling.

For repeating tasks with hour-based cycling the syntax has only minor changes:


    # ...
            graph = foo[T-12] => foo & bar => baz


    # ...
            graph = foo[-PT12H] => foo & bar => baz

Hour-based cycling section names are easy enough to convert, as seen in Table X.

Table 6 Hourly Cycling Sections
Pre-Cylc-6 Cylc-6+
[scheduling][[dependencies]][[[0]]] [scheduling][[dependencies]][[[T00]]]
[scheduling][[dependencies]][[[6]]] [scheduling][[dependencies]][[[T06]]]
[scheduling][[dependencies]][[[12]]] [scheduling][[dependencies]][[[T12]]]
[scheduling][[dependencies]][[[18]]] [scheduling][[dependencies]][[[T18]]]

The graph text in hour-based cycling is also easy to convert, as seen in Table X.

Table 7 Hourly Cycling Offsets
Pre-Cylc-6 Cylc-6+
my_task[T-6] my_task[-PT6H]
my_task[T-12] my_task[-PT12H]
my_task[T-24] my_task[-PT24H] or even my_task[-P1D]

15.11.5. No Implicit Creation of Tasks by Offset Triggers

Prior to cylc-6 intercycle offset triggers implicitly created task instances at the offset cycle points. For example, this pre cylc-6 suite automatically creates instances of task foo at the offset hours 3,9,15,21 each day, for task bar to trigger off at 0,6,12,18:

# Pre cylc-6 implicit cycling.
   initial cycle time = 2014080800
         # This creates foo instances at 03,09,15,21:
         graph = foo[T-3] => bar

Here’s the direct translation to cylc-6+ format:

# In cylc-6+ this suite will stall.
   initial cycle point = 20140808T00
         # This does NOT create foo instances at 03,09,15,21:
         graph = foo[-PT3H] => bar

This suite fails validation with ERROR: No cycling sequences defined for foo, and at runtime it would stall with bar instances waiting on non-existent offset foo instances (note that these appear as ghost nodes in graph visualisations).

To fix this, explicitly define the cycling of with an offset cycling sequence foo:

# Cylc-6+ requires explicit task instance creation.
   initial cycle point = 20140808T00
         graph = foo
         graph = foo[-PT3H] => bar

Implicit task creation by offset triggers is no longer allowed because it is error prone: a mistaken task cycle point offset should cause a failure rather than automatically creating task instances on the wrong cycling sequence.