Tracing & visualisation

Execution report

Nextflow can create an HTML execution report: a single document which includes many useful metrics about a workflow execution. The report is organised in the three main sections: Summary, Resources and Tasks (see below for details).

To enable the creation of this report add the -with-report command line option when launching the pipeline execution. For example:

nextflow run <pipeline name> -with-report [file name]

The report file name can be specified as an optional parameter following the report option.


The Summary section reports the execution status, the launch command, overall execution time and some other workflow metadata. You can see an example below:



The Resources sections plots the distributions of resource usages for each workflow process using the interactive HighCharts plotting library.

Plots are shown for CPU, memory, time and disk read+write. The first three have two tabs with the raw values and a percentage representation showing what proportion of the allocated resources were used. This is helpful to check that job pipeline requests are efficient.



Finally the Tasks section lists all executed tasks reporting for each of them, the status, the actual command script and many other runtime metrics. You can see an example below:



Nextflow collect these metrics running a background process for each job in the target environment. Make sure the following tools are available ps, date, sed, egrep, awk in the system where the jobs are executed. Moreover some of these metrics are not reported when using a Mac OSX system. See the note message about that in the Trace report below.


A common problem when using a third party container image is that it does not ship one or more of the above utilities resulting in an empty execution report.

Please read Report scope section to learn more about the execution report configuration details.

Trace report

Nextflow creates an execution tracing file that contains some useful information about each process executed in your pipeline script, including: submission time, start time, completion time, cpu and memory used.

In order to create the execution trace file add the -with-trace command line option when launching the pipeline execution. For example:

nextflow run <pipeline name> -with-trace

It will create a file named trace.txt in the current directory. The content looks like the above example:

task_id hash native_id name status exit submit duration walltime %cpu rss vmem rchar wchar
19 45/ab752a 2032 blast (1) COMPLETED 0 2014-10-23 16:33:16.288 1m 5s 0.0% 29.8 MB 354 MB 33.3 MB 0
20 72/db873d 2033 blast (2) COMPLETED 0 2014-10-23 16:34:17.211 30s 10s 35.7% 152.8 MB 428.1 MB 192.7 MB 1 MB
21 53/d13188 2034 blast (3) COMPLETED 0 2014-10-23 16:34:17.518 29s 20s 4.5% 289.5 MB 381.6 MB 33.3 MB 0
22 26/f65116 2035 blast (4) COMPLETED 0 2014-10-23 16:34:18.459 30s 9s 6.0% 122.8 MB 353.4 MB 33.3 MB 0
23 88/bc00e4 2036 blast (5) COMPLETED 0 2014-10-23 16:34:18.507 30s 19s 5.0% 195 MB 395.8 MB 65.3 MB 121 KB
24 74/2556e9 2037 blast (6) COMPLETED 0 2014-10-23 16:34:18.553 30s 12s 43.6% 140.7 MB 432.2 MB 192.7 MB 182.7 MB
28 b4/0f9613 2041 exonerate (1) COMPLETED 0 2014-10-23 16:38:19.657 1m 30s 1m 11s 94.3% 611.6 MB 693.8 MB 961.2 GB 6.1 GB
32 af/7f2f57 2044 exonerate (4) COMPLETED 0 2014-10-23 16:46:50.902 1m 1s 38s 36.6% 115.8 MB 167.8 MB 364 GB 5.1 GB
33 37/ab1fcc 2045 exonerate (5) COMPLETED 0 2014-10-23 16:47:51.625 30s 12s 59.6% 696 MB 734.6 MB 354.3 GB 420.4 MB
31 d7/eabe51 2042 exonerate (3) COMPLETED 0 2014-10-23 16:45:50.846 3m 1s 2m 6s 130.1% 703.3 MB 760.9 MB 1.1 TB 28.6 GB
36 c4/d6cc15 2048 exonerate (6) COMPLETED 0 2014-10-23 16:48:48.718 3m 1s 2m 43s 116.6% 682.1 MB 743.6 MB 868.5 GB 42 GB
30 4f/1ad1f0 2043 exonerate (2) COMPLETED 0 2014-10-23 16:45:50.961 10m 2s 9m 16s 95.5% 706.2 MB 764 MB 1.6 TB 172.4 GB
52 72/41d0c6 2055 similarity (1) COMPLETED 0 2014-10-23 17:13:23.543 30s 352ms 0.0% 35.6 MB 58.3 MB 199.3 MB 7.9 MB
57 9b/111b5e 2058 similarity (6) COMPLETED 0 2014-10-23 17:13:23.655 30s 488ms 0.0% 108.2 MB 158 MB 317.1 MB 9.8 MB
53 3e/bca30f 2061 similarity (2) COMPLETED 0 2014-10-23 17:13:23.770 30s 238ms 0.0% 6.7 MB 29.6 MB 190 MB 91.2 MB
54 8b/d45b47 2062 similarity (3) COMPLETED 0 2014-10-23 17:13:23.808 30s 442ms 0.0% 108.1 MB 158 MB 832 MB 565.6 MB
55 51/ac19c6 2064 similarity (4) COMPLETED 0 2014-10-23 17:13:23.873 30s 6s 0.0% 112.7 MB 162.8 MB 4.9 GB 3.9 GB
56 c3/ec5f4a 2066 similarity (5) COMPLETED 0 2014-10-23 17:13:23.948 30s 616ms 0.0% 10.4 MB 34.6 MB 238 MB 8.4 MB
98 de/d6c0a6 2099 matrix (1) COMPLETED 0 2014-10-23 17:14:27.139 30s 1s 0.0% 4.8 MB 42 MB 240.6 MB 79 KB

The following table shows the fields that can be included in the execution report:

Name Description
task_id Task ID.
hash Task hash code.
native_id Task ID given by the underlying execution system e.g. POSIX process PID when executed locally, job ID when executed by a grid engine, etc.
process Nextflow process name.
tag User provided identifier associated this task.
name Task name.
status Task status.
exit POSIX process exit status.
module Environment module used to run the task.
container Docker image name used to execute the task.
cpus The cpus number request for the task execution.
time The time request for the task execution
disk The disk space request for the task execution.
memory The memory request for the task execution.
attempt Attempt at which the task completed.
submit Timestamp when the task has been submitted.
start Timestamp when the task execution has started.
complete Timestamp when task execution has completed.
duration Time elapsed to complete since the submission.
realtime Task execution time i.e. delta between completion and start timestamp.
queue The queue that the executor attempted to run the process on.
%cpu Percentage of CPU used by the process.
%mem Percentage of memory used by the process.
rss Real memory (resident set) size of the process. Equivalent to ps -o rss .
vmem Virtual memory size of the process. Equivalent to ps -o vsize .
* peak_rss Peak of real memory. This data is read from field VmHWM in /proc/$pid/status file.
* peak_vmem Peak of virtual memory. This data is read from field VmPeak in /proc/$pid/status file.
* rchar Number of bytes the process read, using any read-like system call from files, pipes, tty, etc. This data is read from file /proc/$pid/io.
* wchar Number of bytes the process wrote, using any write-like system call. This data is read from file /proc/$pid/io.
* syscr Number of read-like system call invocations that the process performed. This data is read from file /proc/$pid/io.
* syscw Number of write-like system call invocations that the process performed. This data is read from file /proc/$pid/io.
* read_bytes Number of bytes the process directly read from disk. This data is read from file /proc/$pid/io.
* write_bytes Number of bytes the process originally dirtied in the page-cache (assuming they will go to disk later). This data is read from file /proc/$pid/io.


Fields marked with (*) are not available when running the tracing on Mac OSX. Also note that the Mac OSX default date utility, has a time resolution limited to seconds. For a more detailed time tracing it is suggested to install GNU coreutils package that includes the standard one.


These numbers provide an estimation of the resources used by running tasks. They should not be intended as an alternative to low level performance analysis provided by other tools and they may not be fully accurate, in particular for very short tasks (taking less than one minute).

Trace report layout and other configuration settings can be specified by using the nextflow.config configuration file.

Please read Trace scope section to learn more about it.

Timeline report

Nextflow can render an HTML timeline for all processes executed in your pipeline. An example of the timeline report is shown below:


Each bar represents a process run in the pipeline execution. The bar length represents the task duration time (wall-time). The colored area in each bar represents the real execution time. The grey area to the left of the colored area represents the task scheduling wait time. The grey area to the right of the colored area represents the task termination time (clean-up and file un-staging). The numbers on the x-axis represent the time in absolute units eg. minutes, hours, etc.

Each bar displays two numbers: the task duration time and the virtual memory size peak.

As each process can spawn many tasks, colors are used to identify those tasks belonging to the same process.

To enable the creation of the timeline report add the -with-timeline command line option when launching the pipeline execution. For example:

nextflow run <pipeline name> -with-timeline [file name]

The report file name can be specified as an optional parameter following the timeline option.

DAG visualisation

A Nextflow pipeline is implicitly modelled by a direct acyclic graph (DAG). The vertices in the graph represent the pipeline’s processes and operators, while the edges represent the data connections (i.e. channels) between them.

The pipeline execution DAG can be outputted by adding the -with-dag option to the run command line. It creates a file named containing a textual representation of the pipeline execution graph in the DOT format.

The execution DAG can be rendered in a different format by specifying an output file name which has an extension corresponding to the required format. For example:

nextflow run <script-name> -with-dag flowchart.png

List of supported file formats:

Extension File format
dot Graphviz DOT file
html HTML file
pdf PDF file (*)
png PNG file (*)
svg SVG file (*)


The file formats marked with a * require the Graphviz tool installed in your computer.

The DAG produced by Nextflow for the Shootstrap pipeline: