Reviewed by Aditya Kumar · Last reviewed 2026-03-24
**Why Delta Log matters**: Enables ACID, time travel, schema evolution. **Format**: JSON files in `_delta_log/`; each transaction = new file. Records add/remove file actions, metadata. **Significance**: Single source of truth for table state; concurrent readers see consistent...
Why Delta Log matters: Enables ACID, time travel, schema evolution. Format: JSON files in _delta_log/; each transaction = new file. Records add/remove file actions, metadata. Significance: Single source of truth for table state; concurrent readers see consistent snapshot. Scalability trade-offs: Log grows; VACUUM removes old files beyond retention. Cost implications: Log = small storage; many small transactions = many small log files. Best practice: Don't edit manually; use Delta APIs; run VACUUM for old files.
Red Flag: Manually deleting _delta_log files. Pro-Move: 'We run VACUUM weekly; retention 7 days—log stays small.'
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