Observed Signal · Jun 4, 2026 · Technical Release · Source: DEV Community · Impact: 2/5 · Sentiment: Negative
Redis RDB+AOF Hybrid Persistence Silently Lost Data
A developer incident report reproduces and explains data loss caused by Redis’s RDB+AOF hybrid persistence under specific restart timing. The author observed inventory keys vanish after a SIGKILL during a rolling restart: an RDB snapshot had just been written while recent writes had not been fsynced to the AOF, and a truncated AOF caused incomplete commands to be discarded on restart. The post documents a test harness (Docker + pytest + docker-py) used to reproduce 30 failure scenarios, includes code snippets and recommended Redis config used in tests (e.g., aof-use-rdb-preamble yes, appendfsync everysec, save 5 1), and argues for systematic fault-injection testing to validate persistence guarantees in production systems.
Highlights a reproducible, real-world data-durability bug in a widely used infrastructure component (Redis) and provides a test harness to validate persistence — important for engineering reliability but not a platform-level policy change.
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Key Takeaways & Evidence Grounding
- Author reproduced 30 failure scenarios demonstrating silent data loss with Redis RDB+AOF hybrid persistence.
- Root cause: during a kill -9 at a precise timing, an RDB snapshot contained no recent writes while the AOF had truncated final commands; Redis discarded incomplete AOF commands on restart, losing those writes.
- Test harness used Docker containers, pytest, and docker-py to automate fault injection (SIGKILL, abrupt stops) and verify data integrity across restarts.
- Test Redis configuration examples included: --appendonly yes, --aof-use-rdb-preamble yes, --save 5 1 (RDB), and --appendfsync everysec (AOF fsync every second).
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