Redo Log Buffer

The redo log buffer is a circular buffer located in the System Global Area (SGA) that stores redo entries, which describe changes made to the database.

What is a Redo Log Buffer?

A redo record is a data structure containing the necessary information to reconstruct changes made to the database through Data Manipulation Language (DML) or Data Definition Language (DDL) operations. During database recovery, redo entries are applied to data files to restore lost changes.

How the Redo Log Buffer Works

1. Data Copying: The database processes copy redo entries from user memory into the redo log buffer in the SGA. These entries occupy continuous, sequential space within the buffer.
2. Log Writer Process: The Log Writer process (LGWR) is responsible for writing the contents of the redo log buffer to the active online redo log group on disk.
3. Performance Advantage: LGWR writes redo entries sequentially to disk, while the Database Writer process (DBW) performs scattered writes of data blocks. Scattered writes are generally slower than sequential writes, allowing LGWR to enhance performance by minimizing user wait times for DBW to complete its slower operations.