appendingonly

Append-only, or appending-only, is a data management principle in which data records can be added but existing records cannot be modified or deleted in place. In these systems, new entries are appended to a log or data structure, preserving a complete, time-ordered history. Direct edits or erasures are disallowed by policy or enforced by the storage layer, making data effectively immutable after creation.

Common contexts include log files, write-ahead logs used by databases, event-sourced architectures, and distributed log systems with time-ordered streams. Blockchain-like ledgers and certain archival storage implementations also use append-only semantics to guarantee tamper-evidence and recoverability. Some implementations enforce append-only behavior at the software level, while others rely on filesystem features or dedicated WORM (write-once, read-many) storage.

Implementation notes: append-only storage typically uses sequential writes to a log, with indices or snapshots to reconstruct the current state. Deletions or updates are represented as new entries that mark previous data as obsolete via tombstones or versioning records.

Advantages include improved data integrity and auditability, straightforward replication and recovery, and predictable write performance for sequential workloads. Limitations involve unbounded data growth requiring retention and compaction or archival policies, potential read-time complexity to reconstruct the current state, and privacy concerns associated with retaining complete histories.

See also: append-only log, write-ahead log, event sourcing, blockchain, immutability, WORM storage.