seniorHadoop
What is Hadoop job counters and why are they important?
Updated May 16, 2026
Short answer
Counters are global metrics that track job statistics like records processed, errors, and bytes read/written.
Deep explanation
Hadoop counters provide a way to monitor job execution without logging overhead. They are aggregated across mappers and reducers and are useful for debugging, performance tuning, and auditing data pipelines.
Real-world example
Tracking number of malformed records in ETL pipelines.
Common mistakes
- Overusing counters for high-cardinality metrics.
Follow-up questions
- Are counters thread-safe?
- What is limitation of counters?