Why does the runahead limit in c8 show a difference number to c7?

Cylc Cylc 8 Migration
1

hi

i’m porting a workflow to c8 and i’m getting this warning when i run cylc val .

WARNING -  * (8.0.0) [scheduling]max active cycle points -> [scheduling]runahead limit - "4" -> "P3"

why is the number different?

thanks

2

Cylc 7 had max active cycle points (integer number of points) and runahead limit (time interval) as alternate ways of limiting runahead to future cycle points.

The original intention for “max active cycle points” was to literally count cycle points with active tasks in them, which would not necessarily be sequential, but it ended up just being sequential.

Cylc 8 therefore drops the pretense and just has a runahead limit, but you can specify it as an integer “cycle point interval” for any workflow, or as a time interval for datetime cycling workflows:

  • P3H means 3 hours from the oldest active point
    • (the number of cycles depends on your datetime cycling intervals)
  • P3 means 3 “cycle point intervals” (integer or datetime) from the oldest active point
    • 4 --> P3 because P3 is an interval (there are 3 gaps between 4 points).
1 Like
3

hi hilary,

ok great thanks a lot for that, makes sense! i wasn’t aware that runahead limit existed in c7

you can specify it as an integer “cycle point interval” for any workflow, or as a time interval for datetime cycling workflows

ah nice, this will be very useful going forward.

thanks again

jonny