Immediate deletion of some resources may result in inconsistency or data loss and requires confirmation.
The physical organization in a logical standby database is different from that of the primary database, even though the logical standby database is created from a backup copy of the primary database, redo log buffer is used for logging the events that has happened in database, that is it is used for keeping the track of changes that is taking place to a particular database. In addition, a database transaction symbolizes a unit of work performed within a database management system (or similar system) against a database, and treated in a coherent and reliable way independent of other transactions.
By sharing a common relational database, errors and data maintenance costs associated with duplicate data are virtually eliminated, every change made to the database is written to the redo log buffer before it is written to the data block buffer written to the redo log file before it is written to the data file, there, data retrieval is the slowest operation in a database, therefore the data manager needs to be smart enough to get and keep data in memory buffers.
Initially, the database system attempts to import redo log entries still present in the log area when it does the recovery, prior to performing any modification to database, an update log record is created to reflect that modification, also, in simple terms, an undo entry provides the values of data stored before a change and the redo entry provides the values of data stored after a change.
Transactions in a database produce redo entries in the redo log buffer (in memory), and that is always being written to the online redo logs, when you recover the database using redo data, the database reads the change vectors in the redo records and applies the changes to the relevant blocks, consequently, identifying the reasons of security violation in a database is a recent point of consideration.
Note that immediate deletion of some resources may result in inconsistency or data loss and requires confirmation, during the roll forward phase of recovery, the redo logs are sequentially applied to the data blocks, subsequently, meaning that more redo data has been written to redo log file and consecutively more archive logs gets generated.
Is made up of a group of change vectors, each of which is a description of a change made to a single block in the database, all redo log entries in the current and active logs are applied to data files to reconstruct changes made after the most recent checkpoint, particularly, to keep the redo log file dumps as clean as possible, you need a database with no activity.
Rolling forward the database involves applying whatever log records are currently in the redo queue on the mirror server, physically, a log is a file listing changes to the database, stored in a stable storage format. In addition, if you keep events in a transaction log, it starts to behave like a version control system for data (versus code) .
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