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The changes are first recorded in the log, which must be written to stable storage, before the changes are written to the database. [2] The main functionality of a write-ahead log can be summarized as: [3] Allow the page cache to buffer updates to disk-resident pages while ensuring durability semantics in the larger context of a database system.
Write-ahead logging: Any change to an object is first recorded in the log, and the log must be written to stable storage before changes to the object are written to disk. Repeating history during Redo: On restart after a crash, ARIES retraces the actions of a database before the crash and brings the system back to the exact state that it was in ...
there is stable storage at each node with a write-ahead log, no node crashes forever, the data in the write-ahead log is never lost or corrupted in a crash, and; any two nodes can communicate with each other. The last assumption is not too restrictive, as network communication can typically be rerouted.
In particular, the logging mechanism is called write-ahead log (WAL) and allows durability by buffering changes to the disk before they are synchronized from the main memory. In this way, by reconstruction from the log file, all committed transactions are resilient to system-level failures, because they can be redone.
In write ahead logging, durability is guaranteed by writing the prospective change to a persistent log before changing the database. That allows the database to return to a consistent state in the event of a crash. In shadowing, updates are applied to a partial copy of the database, and the new copy is activated when the transaction commits.
Two main parts of it are an in-memory database and a Lua application server. Tarantool maintains data in memory and ensures crash resistance with write-ahead logging and snapshotting. It includes a Lua interpreter and interactive console, but also accepts connections from programs in several other languages.
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Write-ahead log (WAL) shipping: The storage engine's low-level write-ahead log is replicated, ensuring identical data structures across nodes. Logical (row-based) replication : Changes are described at the row level using a dedicated log format, providing greater flexibility and independence from storage engine internals.