appendonlylogg

Appendonlylogg is a term used to describe a design pattern and set of implementations for durable, append-only logging of events or records. In an append-only log, new data is written to the end of a log file or stream and existing entries are never modified in place. This model supports high-throughput writes, simple recovery, and strong auditability, and it is widely used in distributed systems and data storage layers.

An appendonlylogg system typically includes a write path that appends records to log segments, segment rotation, and an index to locate records. Logs are often partitioned by streams and may be replicated for fault tolerance. Storage is organized into segments that are compacted or trimmed to remove stale data while preserving history. Recovery proceeds by replaying the log from a checkpoint or from the start.

Core guarantees include durability (entries persist before acknowledgment), order (preserved by segment), and recoverability (state rebuilt by re-reading the log). Many designs support batch appends and atomic commits for multi-record operations, with delivery semantics ranging from at-least-once to exactly-once. Scaling is typically achieved via partitioning and replication.

Use cases include event sourcing, auditable history, and distributed messaging. Limitations include growing storage needs, background compaction overhead, and complexity of recovery in large clusters. The concept relates to write-ahead logs and log-structured storage used in databases and message systems.