PyTorch Lightning + torch.compile: MisconfigurationException on self.log
Training a Lightning model with torch.compile crashes in the logger connector with a 'called self.log twice with different arguments' MisconfigurationException raised inside the compiled region. Dynamo traces through Lightning's result collection and the metadata-equality branch raises instead of breaking the graph. Insert a graph break or compile only the model forward.
Training a Lightning model with torch.
What this failure is
PyTorch Lightning + torch.compile: MisconfigurationException on self.log is a Training Stability failure seen during ML training runs. Training a Lightning model with torch.compile crashes in the logger connector with a 'called self.log twice with different arguments' MisconfigurationException raised inside the compiled region. Dynamo traces through Lightning's result collection and the metadata-equality branch raises instead of breaking the graph. Insert a graph break or compile only the model forward. Common tags: Pytorch Lightning, Torch Compile, Dynamo, Graph Break.
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Why it happens (the mechanism)
Torch.compile/Dynamo traces through Lightning's _ResultCollection logging path. The metadata-equality check raises inside the compiled graph instead of being a normal control-flow branch, so a harmless re-log turns into an exception. Taken together, these mechanisms explain why the failure is reproducible, why it tends to surface on specific workloads or scales, and why generic mitigation attempts often fall short without addressing the underlying cause.
What you'll observe
- torch.compile + Lightning crashes during logging
- A benign re-log path becomes a hard exception
- Removing torch.compile makes the error disappear
Common symptoms and what they mean
| Symptom | Why it happens |
|---|---|
| MisconfigurationException: You called self.log(...) twice in ... with different arguments | torch.compile/Dynamo traces through Lightning's _ResultCollection logging path |
| Traceback through logger_connector/result.py _ResultCollection | The metadata-equality check raises inside the compiled graph instead of being a normal control-flow branch, so a harmless re-log turns into an exception |
| Only occurs with torch.compile enabled | torch.compile/Dynamo traces through Lightning's _ResultCollection logging path |
Which systems are affected
- PyTorch Lightning 2.x + torch.compile
- Compiling the LightningModule/training loop (not just the inner model)
- self.log calls inside compiled forward/step
How to confirm this is the problem
Use this checklist to test the hypothesis against a small reproduction. No single line proves the root cause, so preserve the preceding events and compare one variable at a time.
- ✓Reproduce the failure from a clean checkpoint/seed: the symptom must appear without warm-up state from a previous run.
- ✓Verified signal present: MisconfigurationException: You called self.log(...) twice in ... with different arguments
- ✓Verified signal present: Traceback through logger_connector/result.py _ResultCollection
- ✓Verified signal present: Only occurs with torch.compile enabled
- ✓A targeted fix from the "How to fix it" section eliminates or substantially reduces the symptom within one validation pass.
The fix and the prevention pattern
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Root cause
- torch.compile/Dynamo traces through Lightning's _ResultCollection logging path
- The metadata-equality check raises inside the compiled graph instead of being a normal control-flow branch, so a harmless re-log turns into an exception
The fix and how to prevent it
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