Model Retraining

Overview

The Model Retraining API allows authorized users to trigger retraining of the demand prediction model with updated transaction data. This endpoint fetches the latest purchase and sales data, trains a new model, and deploys it for predictions.

Base URL

https://your-domain.com/v1/ml

Retrain Model

POST /v1/ml/retrain

Triggers a model retraining operation using fresh transaction data. Authentication: Required (JWT or internal service key) Authorization: Configurable permissions (typically requires admin role)

Model retraining is a resource-intensive operation that may take several minutes. Use with caution and avoid triggering multiple concurrent retraining jobs.

Request Body

start_date

string

Start date for training data (ISO 8601: YYYY-MM-DD). Optional - defaults to earliest available data.

end_date

string

End date for training data (ISO 8601: YYYY-MM-DD). Optional - defaults to most recent data.

{
  "start_date": "2024-01-01",
  "end_date": "2026-03-01"
}

If both start_date and end_date are omitted, the model will train on all available historical data.

Response

version

string

Version identifier of the newly trained model

metrics

object

Model performance metrics on test set

metrics.mae

number

Mean Absolute Error

metrics.rmse

number

Root Mean Square Error

metrics.mape

number

Mean Absolute Percentage Error

metrics.r2

number

R-squared (coefficient of determination)

trained_at

string

Training completion timestamp (ISO 8601)

samples

object

Dataset split information

samples.train

integer

Number of training samples

samples.test

integer

Number of test samples

samples.total

integer

Total number of samples

{
  "version": "v1.3.0-20260306",
  "metrics": {
    "mae": 1.32,
    "rmse": 1.95,
    "mape": 0.14,
    "r2": 0.87
  },
  "trained_at": "2026-03-06T14:35:22Z",
  "samples": {
    "train": 8540,
    "test": 2135,
    "total": 10675
  }
}

Status Codes

200 OK - Model retrained successfully
400 Bad Request - Invalid date range or parameters
401 Unauthorized - Missing or invalid authentication
403 Forbidden - Insufficient permissions
500 Internal Server Error - Training failed

Example

# Retrain with all available data
curl -X POST https://your-domain.com/v1/ml/retrain \
  -H "Authorization: Bearer YOUR_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{}'

# Retrain with specific date range
curl -X POST https://your-domain.com/v1/ml/retrain \
  -H "Authorization: Bearer YOUR_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "start_date": "2024-01-01",
    "end_date": "2026-03-01"
  }'

Retraining Process

The retraining pipeline follows these steps:

1. Data Extraction

Fetches purchase and sales transactions from sgivu-purchase-sale service
Filters by date range if specified
Aggregates sales by vehicle segment (brand, model, line) and month

2. Feature Engineering

Creates time series features (month, year, seasonality)
Computes segment-level statistics
Generates lag features and rolling aggregates

3. Model Training

Splits data into training (80%) and test (20%) sets
Trains time series forecasting model (typically ARIMA, Prophet, or ML-based)
Validates on test set

4. Model Evaluation

Calculates performance metrics (MAE, RMSE, MAPE, R²)
Compares against previous model if available

5. Model Deployment

Persists model artifacts using joblib
Optionally saves to PostgreSQL
Updates model metadata
Activates as the current production model

Model Versioning

Each trained model is assigned a version identifier: Format: v{major}.{minor}.{patch}-{timestamp} Example: v1.3.0-20260306

major.minor.patch - Semantic version based on algorithm changes
timestamp - Training date in YYYYMMDD format

Version Management

New models automatically become the active model for predictions
Previous model versions are retained for rollback if needed
Model artifacts can be stored in both filesystem and database

Training Data Requirements

Minimum Data Volume

For reliable models, ensure:

Time range: At least 12 months of historical data
Segment coverage: Multiple vehicle segments with sufficient transactions
Sample size: Minimum 100 transactions per segment recommended

Data Quality

Missing or null values are handled automatically
Outliers are detected and may be excluded
Segments with insufficient data are skipped

Training on insufficient data may result in poor model performance. The API will return an error if the dataset is too small.

Performance Metrics Explained

Mean Absolute Error (MAE)

Average absolute difference between predicted and actual sales.

Units: Same as target variable (number of vehicles)
Lower is better
Example: MAE of 1.32 means predictions are off by ~1-2 vehicles on average

Root Mean Square Error (RMSE)

Square root of average squared errors. Penalizes large errors more heavily.

Units: Same as target variable
Lower is better
Typical range: Slightly higher than MAE

Mean Absolute Percentage Error (MAPE)

Average percentage error relative to actual values.

Units: Percentage (0-1)
Lower is better
Example: MAPE of 0.14 means 14% average error

R-squared (R²)

Proportion of variance explained by the model.

Range: 0-1 (can be negative for poor models)
Higher is better
Example: R² of 0.87 means model explains 87% of variance

Interpreting Metrics

Good Model:

MAE < 2.0
RMSE < 3.0
MAPE < 0.20 (20%)
R² > 0.75

Excellent Model:

MAE < 1.0
RMSE < 1.5
MAPE < 0.10 (10%)
R² > 0.90

Best Practices

Retraining Frequency

Recommended schedule:

Weekly: For high-volume dealerships with frequent transactions
Monthly: For moderate-volume operations
Quarterly: For low-volume or stable markets

When to Retrain

Trigger retraining when:

New transaction data is available
Model performance degrades (predictions become less accurate)
Significant market changes occur (seasonality, economic shifts)
New vehicle models are introduced

Monitoring Model Performance

Track these indicators:

Prediction accuracy on recent data
Residual analysis (actual vs. predicted)
Metric trends over time
Coverage (percentage of segments with predictions)

Retraining Schedule

You can automate retraining using cron jobs or scheduled tasks:

Example: Weekly Cron Job

# Retrain every Monday at 2 AM
0 2 * * 1 curl -X POST https://your-domain.com/v1/ml/retrain \
  -H "X-Internal-Service-Key: $INTERNAL_KEY" \
  -H "Content-Type: application/json" \
  -d '{}'

Example: Python Scheduled Task

import requests
import schedule
import time

def retrain_model():
    response = requests.post(
        "https://your-domain.com/v1/ml/retrain",
        headers={
            "X-Internal-Service-Key": "YOUR_KEY",
            "Content-Type": "application/json"
        },
        json={}
    )
    print(f"Retraining status: {response.status_code}")
    print(response.json())

# Schedule weekly retraining
schedule.every().monday.at("02:00").do(retrain_model)

while True:
    schedule.run_pending()
    time.sleep(3600)

Error Responses

400 Bad Request - Invalid Date Range

{
  "detail": "end_date must be after start_date"
}

400 Bad Request - Insufficient Data

{
  "detail": "Insufficient training data. Minimum 12 months of transaction history required."
}

403 Forbidden

{
  "detail": "User does not have required permission: ml:retrain"
}

500 Internal Server Error - Training Failed

{
  "detail": "Model training failed: convergence error. Check data quality and try again."
}

Storage and Persistence

Model Artifacts

Trained models are persisted using joblib:

Location: Configured via MODEL_DIR environment variable
Format: Pickled scikit-learn/XGBoost models
Naming: model_{version}.pkl

Database Persistence

Optionally, model metadata and artifacts can be stored in PostgreSQL:

Table: ml_model_artifacts
Fields: version, metrics, trained_at, artifact_data (binary)

Feature Snapshots

Training features can be saved for reproducibility:

Table: ml_training_features
Purpose: Audit, debugging, retraining experiments

Rollback and Model Management

If a newly trained model performs poorly:

Manual Rollback: Replace current model file with previous version
Database Rollback: Update active model pointer in database
Verify: Test predictions with /predict endpoint

Future versions will include an API endpoint for automated model rollback.

Authentication

User Management

Vehicle Management

Client Management

Purchase & Sales

Machine Learning

​Overview

​Base URL

​Retrain Model

​Request Body

​Response

​Status Codes

​Example

​Retraining Process

​1. Data Extraction

​2. Feature Engineering

​3. Model Training

​4. Model Evaluation

​5. Model Deployment

​Model Versioning

​Version Management

​Training Data Requirements

​Minimum Data Volume

​Data Quality

​Performance Metrics Explained

​Mean Absolute Error (MAE)

​Root Mean Square Error (RMSE)

​Mean Absolute Percentage Error (MAPE)

​R-squared (R²)

​Interpreting Metrics

​Best Practices

​Retraining Frequency

​When to Retrain

​Monitoring Model Performance

​Retraining Schedule

​Example: Weekly Cron Job

​Example: Python Scheduled Task

​Error Responses

​400 Bad Request - Invalid Date Range

​400 Bad Request - Insufficient Data

​403 Forbidden

​500 Internal Server Error - Training Failed

​Storage and Persistence

​Model Artifacts

​Database Persistence

​Feature Snapshots

​Rollback and Model Management

Overview

Base URL

Retrain Model

Request Body

Response

Status Codes

Example

Retraining Process

1. Data Extraction

2. Feature Engineering

3. Model Training

4. Model Evaluation

5. Model Deployment

Model Versioning

Version Management

Training Data Requirements

Minimum Data Volume

Data Quality

Performance Metrics Explained

Mean Absolute Error (MAE)

Root Mean Square Error (RMSE)

Mean Absolute Percentage Error (MAPE)

R-squared (R²)

Interpreting Metrics

Best Practices

Retraining Frequency

When to Retrain

Monitoring Model Performance

Retraining Schedule

Example: Weekly Cron Job

Example: Python Scheduled Task

Error Responses

400 Bad Request - Invalid Date Range

400 Bad Request - Insufficient Data

403 Forbidden

500 Internal Server Error - Training Failed

Storage and Persistence

Model Artifacts

Database Persistence

Feature Snapshots

Rollback and Model Management