Appendonlyloggar

Appendonlyloggar is a term used in computing to describe a design principle and implementation for recording events or data as an append-only log. In an append-only log, new entries are appended to the end of a log stream and existing entries are not modified or deleted in place. The log is usually time-stamped and has a monotonically increasing offset or sequence number.

Key benefits include immutability, straightforward recovery, and strong auditability. Because entries are never overwritten, historical data remains verifiable; recovery from crashes typically involves replaying the log from a known checkpoint. The sequential nature of appends favors high write throughput and simple durability guarantees when backed by reliable storage.

Common use cases include event sourcing, audit trails, transaction logs, and other scenarios where the history of changes must be preserved. Distributed systems and data stores that separate write and read paths rely on append-only logs. Message brokers such as Kafka implement append-only logs per partition, while log-structured file systems and commit logs in databases rely on similar principles.

Design considerations involve storage format (binary or text), segment size and rotation, timestamps, and indexing for efficient access. Retention and compaction strategies, compression, and archival policies determine long-term storage requirements. Replication and disaster recovery plans influence durability, while read patterns affect how much historical data must remain readily accessible versus archived.

Limitations include unbounded growth, the need for retention policies, and potential read amplification for older entries. Practical implementations balance durability, access latency, and storage costs, often combining append-only logs with periodic snapshots, compaction, or pruning to maintain usable state.