TraceRecord field `realtime` differs from documentation

[JosuaCarl]

Bug report

Expected behavior and actual behavior

In the Nextflow documentation realtime is described as

**realtime**
    Task execution time i.e. delta between completion and start timestamp.

I found that this is often not true and quite by a lot. See the following raw trace:

submit	duration	realtime	start	complete
1774271746328	16901	8000	1774271746424	1774271763229
1774271763256	35975	6000	1774271766533	1774271799231

Now you can subtract complete - start.
For the first line this is 1774271763229 - 1774271746424 = 16805. This does not correspond to realtime given at 8000 or exactly 8s.

While the correct value is initially set

nextflow/modules/nextflow/src/main/groovy/nextflow/processor/TaskHandler.groovy

Line 239 in 00f35b3

record.realtime = completeTimeMillis - startTimeMillis

it is replaced a few lines later

nextflow/modules/nextflow/src/main/groovy/nextflow/processor/TaskHandler.groovy

Line 246 in 00f35b3

if(file) record.parseTraceFile(file)

by this value

nextflow/modules/nextflow/src/main/resources/nextflow/executor/command-trace.txt

Line 206 in 9d65b9e

"realtime=$wall_time" \

Steps to reproduce the problem

Run nextflow run nf-core/demo -r 1.1.0 -profile test,docker and look at the execution_trace_<timestamp>.txt file's realtime vs complete - start value.

Environment

• Nextflow version: 25.10.4

Either the documentation is wrong and should be changed or the value should not be overwritten / a new walltime parameter introduced.

[bentsherman]

Indeed, the realtime refers to the walltime of the .command.sh i.e. the user's task script. So it doesn't include everything else in .command.run

There is also a fallback to complete - start if realtime is missing for some reason. I tried to remove this fallback a while ago but it was rejected...

Anyway, the docs just need to be updated here

[JosuaCarl]

Alright, I thought as much, although a 8s delay between the task being set to STARTED and the task actually starting seems quite a lot.

[bentsherman]

Depending on the environment, that delay can encompass things like loading the container and staging input data