DocsAI Training Coach🔧 Fine-Tuning Methods

Full Fine-Tuning

Adjusting all model parameters – maximum control

In full fine-tuning, all parameters of the base model are trained and adjusted. Maximum expressiveness, but maximum memory requirements.

Pros and cons

✓ Advantages

  • Maximum adaptability
  • Best possible performance
  • No extra overhead from adapters
  • Good for fundamental domain shifts

✗ Disadvantages

  • Huge VRAM requirement (~28GB for 7B)
  • Catastrophic forgetting possible
  • Needs much more data
  • Every checkpoint = full model size

Catastrophic forgetting – the main risk

During full fine-tuning, the model can "forget" its general prior knowledge if trained too aggressively on new data. This happens when new knowledge overwrites the old weights.

Countermeasures against catastrophic forgetting:

  1. Low learning rate (1e-5 or lower)
     → Small updates preserve existing knowledge

  2. Few epochs (1–3)
     → Don't grind the model too long into new data

  3. Elastic Weight Consolidation (EWC)
     → Penalizes large changes to important parameters
     → More complex, but effective

  4. Replay (mixed training)
     → Mix of old (general) and new (specific) data
     → e.g. 80% new task + 20% general text

Full fine-tuning vs. LoRA: when to use which?

VRAM < 24 GBLoRA / QLoRAFull FT doesn't fit in memory
VRAM 24–40 GB, maximum performance desiredFull fine-tuning (bf16)Best result when memory allows
Little training data (< 1,000 examples)LoRA (small rank)Fewer trainable parameters = less overfitting
Fast iteration, many experimentsLoRASmaller checkpoints, faster training
Multiple task-specific versions of a modelLoRA adaptersLoad base model once, swap adapters
Model needs to learn fundamentally new knowledgeFull fine-tuningAdjusting all layers for deep changes

Full fine-tuning checklist

Before starting full fine-tuning: ✓ VRAM ≥ 24 GB, ✓ bf16 enabled, ✓ LR at most 5e-5, ✓ at most 3 epochs planned, ✓ early stopping enabled, ✓ best-checkpoint saving on.