Write-Ahead Logging

A Write-Ahead Logging is a database recovery technique that records database changes to a log file before applying them to database files to ensure transaction durability and crash recovery.

• AKA: WAL, Transaction Log, Recovery Log.
• Context:
  • It can typically record Transaction Changes in sequential order.
  • It can typically ensure ACID Properties through log persistence.
  • It can typically enable Point-in-Time Recovery via log replay.
  • It can typically support Database Replication through log streaming.
  • It can typically maintain Checkpoints for recovery optimization.
  • ...
  • It can often implement Log Archiving for long-term retention.
  • It can often compress Log Records for storage efficiency.
  • It can often support Parallel Recovery through log segmentation.
  • It can often enable Hot Backups without database locks.
  • ...
  • It can range from being a Physical Write-Ahead Logging to being a Logical Write-Ahead Logging, depending on its log record format.
  • It can range from being a Synchronous Write-Ahead Logging to being an Asynchronous Write-Ahead Logging, depending on its write timing.
  • ...
  • It can be implemented by PostgreSQL WAL, MySQL InnoDB Log, Oracle Redo Log.
  • It can integrate with Streaming Replication for high availability.
  • It can support Database Clusters through distributed logging.
  • ...
• Example(s):
  • Database-Specific WAL Implementations, such as:
    • PostgreSQL WAL implementing WAL segment files.
    • MySQL Binary Log for replication support.
    • Oracle Redo Log with archived log mode.
  • WAL Operation Modes, such as:
    • Full Page Write WAL for torn page protection.
    • Incremental WAL for storage optimization.
    • Compressed WAL for bandwidth efficiency.
  • WAL Usage Patterns, such as:
    • Replication WAL for standby synchronization.
    • PITR WAL for point-in-time recovery.
    • Archival WAL for compliance requirements.
  • ...
• Counter-Example(s):
  • Shadow Paging, which creates page copies rather than logging change records.
  • In-Memory Database, which may not require persistent logging.
  • Append-Only Storage, which achieves durability without separate log files.
• See: Database Recovery, ACID Transaction, Database Replication, Checkpoint (Database).

---