VizTracer

VizTracer is a low-overhead logging/debugging/profiling tool that can trace and visualize your python code execution.

You can take a look at the demo result of multiple example programs. Use "AWSD" to zoom/navigate. More help can be found by clicking "?" on the top right corner.

trace viewer is used to display the stand alone html data.

VizTracer also supports json output that complies with Chrome trace event format, which can be loaded using perfetto

VizTracer generates HTML report for flamegraph using d3-flamegraph

Highlights

• Detailed function entry/exit information on timeline, not just summary of time used
• Super easy to use, no source code change for basic usage, no package dependency
• Optional function filter to ignore functions you are not interested
• Custom events to log and track arbitrary data through time
• Keep latest entries, dump anytime or auto save at exit
• Stand alone HTML report with powerful front-end, or chrome-compatible json
• Works on Linux/MacOS/Windows

Install

The prefered way to install VizTracer is via pip

pip install viztracer

Basic Usage

Command Line

Assume you have a python script to run:

python3 my_script.py arg1 arg2

You can simply use VizTracer by

viztracer my_script arg1 arg2
# OR
python3 -m viztracer my_script.py arg1 arg2

which will generate a result.html file in the directory you run this command, which you can open with Chrome(use AWSD to navigate/zoom).

You can also generate json file or gz file and load it with chrome://tracing/ or perfetto. gz file is especially helpful when your trace file is large

viztracer -o result.json my_script.py arg1 arg2
viztracer -o result.json.gz my_script.py arg1 arg2

Inline

You can also manually start/stop VizTracer in your script as well.

from viztracer import VizTracer

tracer = VizTracer()
tracer.start()
# Something happens here
tracer.stop()
tracer.save() # also takes output_file as an optional argument

Or, you can do it with with statement

with VizTracer(output_file="optional.html") as tracer:
    # Something happens here

Display Result

By default, VizTracer will generate a stand alone HTML file which you can simply open with Chrome.

However, you can generate json file as well, which complies to the chrome trace event format. You can load the json file on perfetto or chrome://tracing.

When you are dealing with big traces, a stand alone HTML file might be very large and hard to load. You should try to dump a compressed filename.json.gz file

Advanced Usage

Trace Filter

VizTracer can filter out the data you don't want to reduce overhead and keep info of a longer time period before you dump the log.

• max stack depth
• include files
• exclude files
• ignore c function
• sparse log

Extra Logs without Code Change

VizTracer can log extra information without changing your source code

• print() function
• Garbage Collector Operation
• Function Input Arguments
• Function Return Value
• Function Entry
• Any Variable/Attribute with RegEx
• Variables in Specified Function
• Raised Exceptions

Add Custom Event

VizTracer supports inserting custom events while the program is running. This works like a print debug, but you can know when this print happens while looking at trace data.

• Instant Event
• Counter Event
• Object Event
• Arbitrary Value in Function

Check more advanced usage for more features

Misc

Multi Thread Support

VizTracer supports python native threading module without the need to do any modification to your code. Just start VizTracer before you create threads and it will just work.

Multi Process Support

VizTracer supports subprocess with --log_subprocess and multiprocessing or os.fork() with --log_multiprocess. For more general multi-process cases, VizTracer can support with some extra steps.

Refer to multi process docs for details

JSON alternative

VizTracer needs to dump the internal data to json format. It is recommended for the users to install orjson, which is much faster than the builtin json library. VizTracer will try to import orjson and fall back to the builtin json library if orjson does not exist.

Virtual Debug

You can virtually debug your program with you saved json report. The interface is very similar to pdb. Even better, you can go back in time because VizTracer has all the info recorded for you.

vdb <your_json_report>

Refer to the docs for detailed commands

Performance

VizTracer will introduce 2x to 3x overhead in the worst case. The overhead is much better if there are less function calls or if filters are applied correctly.

An example run for test_performance with Python 3.8 / Ubuntu 18.04.4 on Github VM

fib:
0.000678067(1.00)[origin] 
0.019880272(29.32)[py] 0.011103901(16.38)[parse] 0.021165599(31.21)[json] 
0.001344933(1.98)[c] 0.008181911(12.07)[parse] 0.015789866(23.29)[json] 
0.001472846(2.17)[cProfile]  

hanoi     (6148, 4100):
0.000550255(1.00)[origin] 
0.016343521(29.70)[py] 0.007299123(13.26)[parse] 0.016779364(30.49)[json] 
0.001062505(1.93)[c] 0.006416136(11.66)[parse] 0.011463236(20.83)[json] 
0.001144914(2.08)[cProfile] 

qsort     (8289, 5377):
0.002817679(1.00)[origin] 
0.052747431(18.72)[py] 0.011339725(4.02)[parse] 0.023644345(8.39)[json] 
0.004767673(1.69)[c] 0.008735166(3.10)[parse] 0.017173703(6.09)[json] 
0.007248019(2.57)[cProfile] 

slow_fib  (1135, 758):
0.028759652(1.00)[origin] 
0.033994071(1.18)[py] 0.001630461(0.06)[parse] 0.003386635(0.12)[json] 
0.029481623(1.03)[c] 0.001152415(0.04)[parse] 0.002191417(0.08)[json] 
0.028289305(0.98)[cProfile] 

Documentation

For full documentation, please see https://viztracer.readthedocs.io/en/stable

Bugs/Requests

Please send bug reports and feature requests through github issue tracker. VizTracer is currently under development now and it's open to any constructive suggestions.

License

Copyright Tian Gao, 2020.

Distributed under the terms of the Apache 2.0 license.