What is Redo Apply?
Redo Apply performs the task of creating a block-by-block copy of the Primary database. The operations are as follows;
- The RFS process writes the Redo Data received from the LNS process to the “Standby Redo Log” file.
- Redo Apply Writes redo data read from the “Standby Redo Log” file into the memory area and processes the changed vectors directly into the Standby database.
- Redo Apply runs operations in parallel for performance. Parallel recovery is performed with the MRP process that manages multiple apply operations. Combines and parses redo data according to SCN number.
Redo Apply protects the Primary database against block corruption. Redo transfer is performed directly from the SGA , completely isolated from physical I / O corruption on the primary database side. Data Guard performs “Validate” against block corruption before applying redo data to the Standby database.
Corruption validation requirements;
- The DB_ULTRA_SAFE parameter should be set on the primary database side.
- On the stand-by database side, DB_BLOCK_CHECKSUM=FULL and DB_LOST_WRITE_PROTECT=TYPICAL parameters must be set.
If Redo Apply detects “Corrupted” redo data in the Standby database, it automatically tries to repair the corrupted redo data by reading it from the “Archive Log” files.
If you want to learn more about Oracle Data Guard, you may want to read below articles;
“Oracle Data Guard Architecture“,
“Oracle Data Guard Redo Transport Services“