Recoverability and Deadlock Avoidance
The first reason listed for using transactions was recoverability. Any logical change to a database may require multiple changes to underlying data structures. For example, modifying a record in a Btree may require leaf and internal pages to split, so a single DB→put method call can potentially require that multiple physical database pages be written. If only some of those pages are written and then the system or application fails, the database is left inconsistent and cannot be used until it has been recovered; that is, until the partially completed changes have been undone.
Write-ahead-logging is the term that describes the underlying implementation that Berkeley DB uses to ensure recoverability. What ...
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