Databaselogs

Databaselogs are records generated by a database system that detail changes to data and the state of the database over time. They provide durability, enable recovery after crashes, support replication, auditing, and analysis. Logs are typically written as part of a write-ahead protocol and stored in dedicated log files or streams.

Most database systems separate data files from log records. The logs can be physical, recording page images and transaction boundaries, or logical, recording high-level operations such as inserted rows. Common log types include transaction or redo logs (used to redo committed transactions after a crash) and undo logs (used to roll back uncommitted transactions). Some systems use a binary log or WAL (write-ahead log) to ensure forward recovery.

Use in recovery: during crash recovery, the system reads logs to reapply or undo operations to reach a consistent state. For replication, logs are shipped to standby servers to reproduce the primary's state. For auditing, logs provide a trail of changes, user activity, and schema modifications.

Management: logs grow over time and can affect storage and performance, so administrators implement rotation, retention, compression, archiving, and, where required, encryption and access controls. Security considerations include protecting logs from tampering and restricting access.

Examples: PostgreSQL uses the WAL system; MySQL uses the binary log or general log; Oracle maintains redo logs; SQL Server uses a transaction log. Effective databaselogs practices include ensuring recoverability, regular backups of logs, and tests of point-in-time recovery.