Block devices are disks or memory regions in which data is accessed in blocks. Linux block devices are generally accessed through I/O buffers. However, Linux block devices can also be accessed directly, and Oracle uses direct I/O to write to its redo logs. It is therefore important for Replication Agent to directly read from the block devices on which Oracle redo logs are stored. Otherwise, stale or nonexistent block data from device I/O buffers may interfere with replication.
Use the lr_direct_read parameter to indicate how Replication Agent reads Oracle redo logs.
If lr_direct_read is true, Replication Agent reads Oracle redo log files directly on Linux, bypassing block device I/O buffers.