Redo Log – The most crucial structure for recovery operations is the redo log, which consists of two or more preallocated files that store all changes made to the database as they occur. Every instance of an Oracle Database has an associated redo log to protect the database in case of an instance failure (link). The database requires a minimum of two files to guarantee that one is always available for writing while the other is being archived (if the database is in ARCHIVELOG mode). LGWR (log writer) writes to redo log files in a circular fashion. When the current redo log file fills, LGWR begins writing to the next available redo log file. When the last available redo log file is filled, LGWR returns to the first redo log file and writes to it, starting the cycle again. This enables you to restore your database to any point in time.
A Data Guard configuration involves log transfer and log apply services on individual sites to manage the standby database. Log transfer and log apply services on all the sites should be performing well enough that a redo log file should be archived and applied to the Oracle instance in near real-time.
The DBA needs to understand the redo generation rate of the primary database before the tuning objective can be quantified.
Data Guard – A data protection and availability solution for Oracle databases. The basic function of Oracle Data Guard is to keep a synchronized copy of a database as standby, in order to make provision, in case the primary database is inaccessible to end users (link).
Odlično objašnjenje o vezi redo logova i Data Guard-a : link
ODI – Oracle Data Integrator – data integration software product