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Log shipping is the process of automating the backup of transaction log files on a primary (production) database server, and then restoring them onto a standby server. This technique is supported by Microsoft SQL Server , [ 1 ] 4D Server , [ 2 ] MySQL , [ 3 ] and PostgreSQL .
Re-doing a transaction in this context simply means applying the information in the redo log files to the database; the system does not re-run the transaction itself.) The system thus re-creates committed transactions by applying the “after image” records in the redo log files to the database, and undoes incomplete transactions by using the ...
SQL refers to Structured Query Language, a kind of language used to access, update and manipulate database. In SQL, ROLLBACK is a command that causes all data changes since the last START TRANSACTION or BEGIN to be discarded by the relational database management systems (RDBMS), so that the state of the data is "rolled back" to the way it was before those changes were made.
undoNextLSN: This field contains the LSN of the next log record that is to be undone for transaction that wrote the last Update Log. Commit Record notes a decision to commit a transaction. Abort Record notes a decision to abort and hence roll back a transaction. Checkpoint Record notes that a checkpoint has been made. These are used to speed up ...
The TSM database (through release 5.5) was a bespoke B+ tree database; although the TSM database used many of the same underlying technologies as IBM's Db2, has a SQL engine (for read-only use), and supports access through ODBC, the database had an architectural limit of approximately 530 GB, and 13 GB of log space. Starting with TSM 6.1 ...
A write ahead log is an append-only auxiliary disk-resident structure used for crash and transaction recovery. 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]
A transaction is typically started using the command BEGIN (although the SQL standard specifies START TRANSACTION). When the system processes a COMMIT statement, the transaction ends with successful completion. A ROLLBACK statement can also end the transaction, undoing any work performed since BEGIN.
Restore can be used to apply a single backup, or it can be used to apply a combination of a single full backup with one or more incremental backups. Further, any existing log files can be replayed as well to recreate an entire data set all the way up to the last transaction logged as committed to transaction level 0.