Executing DVC pipelines

Introduction to Data Versioning with DVC

Ravi Bhadauria

Machine Learning Engineer

Recap

Preprocessing stage

stages:
  preprocess:
    cmd: python3 preprocess.py
    params:
      - preprocess
    deps:
    - preprocess.py
    - raw_data.csv
    outs:
    - processed_data.csv

Training and evaluation

stages:
  train_and_evaluate:
    cmd: python3 train_and_evaluate.py
    params:
      - train_and_evaluate
    deps:
    - processed_data.csv
    - train_and_evaluate.py
    outs:
    - plots.png
    - metrics.json

Reproducing a pipeline

Reproduce the pipeline using dvc repro

$ dvc repro

Running stage 'preprocess':                                      
> python preprocess.py

Running stage 'train_and_evaluate':
> python train_and_evaluate.py
Updating lock file 'dvc.lock'

A state file dvc.lock is generated
- Similar to .dvc file, captures MD5 hashes

$ git add dvc.lock && git commit -m "first pipeline run"

Using cached results

Using cached results to speed up iteration

$ dvc repro

Stage 'preprocess' didn't change, skipping
Running stage 'train_and_evaluate' with command: ...

Stage caching in DVC

Flowchart of how stage caching works in DVC

Dry running a pipeline

Use --dry flag to only print commands without running the pipeline

$ dvc repro --dry

Running stage 'preprocess':
> python3 preprocess_dataset.py

Running stage 'train_and_evaluate':
> python3 train_and_evaluate.py

Additional arguments

Running specific files dvc repro linear/dvc.yaml
- Multiple dvc.yaml in one folder are not allowed
Running specific stages dvc repro <target_stage>
- This will also run upstream dependencies
Force run a pipeline/stage dvc repro -f
Not storing execution outputs in cache dvc repro --no-commit
- Use dvc commit later

Parallel stage execution

Schematic of parallel stage execution DAG in DVC

Run independent steps concurrently

# Run A2 and its upstream dependencies
$ dvc repro A2

# Run B2 and its upstream dependencies
$ dvc repro B2

Use caching to speed up execution

$ dvc repro train

Stage 'A2' didn't change, skipping
Stage 'B2' didn't change, skipping
Running stage 'train' with command: ...

Let's practice!

Introduction to Data Versioning with DVC