Redis Persistence Mechanisms: RDB Snapshots, AOF Logging, and Hybrid Persistence
This article explains Redis's persistence strategies—including RDB snapshotting with Copy‑On‑Write, AOF command logging with configurable fsync policies, and the hybrid persistence introduced in Redis 4.0—detailing their implementation, performance trade‑offs, configuration options, and practical usage examples.
Redis stores data in memory, so persistence mechanisms are needed to avoid data loss on crashes.
Two main persistence methods are described: RDB snapshots (binary dump of the dataset) and AOF logs (append‑only file of write commands). The article explains the Copy‑On‑Write technique used by RDB, the fork‑based snapshot process, and the AOF write‑and‑fsync strategies, including the three fsync policies ( no , always , everysec ).
Code examples illustrate the use of fork() in C and Redis commands such as bgsave , bgrewriteaof , and appendfsync . The process of AOF rewriting (log slimming) is detailed, showing how a long AOF can be compacted into a shorter set of commands.
Redis 4.0 introduces hybrid persistence, which combines an RDB‑style snapshot with incremental AOF entries, improving restart speed. A table of relevant configuration parameters (save, appendonly, appendfsync, etc.) and their meanings is provided.
The article concludes that hybrid persistence is recommended for production environments, balancing performance and data safety.
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