Understanding redo (5) Deep Learning RBA

1 Definition

RBA is the address corresponding to redo entries in the redo log file.

2 components

RBA consists of three parts:

Serial number (4 bytes)

Block number (4 bytes)

Start byte (2 bytes)

All of the above are in hexadecimal storage.

3 type

3.1 LRBA

Definition: Position of the redo entries corresponding to the first dirty block in the redo log file

Note: The CKPT-Q maintains dirty blocks in the order of LRBA, and DBWn writes from the CKPT-Q in the order of LRBA when a checkpoint event is executed. LRBA is the checkpoint position. From the checkpoint location (LRBA), the redo record is applied to the On disk rba. This process is rollback.

3.2 HRBA

Definition: Location of the redo entries generated when a dirty block is last updated in the buffer cache in the redo log file

NOTE: If HRBA> on-disk RABA, the related redo entries of HRBA are still in redo log buffer. If the instance is crash, HRBA cannot be recovered.

3.3 checkpoint RBA

Definition: LRBA, the first dirty data block in the CKPT-Q, the dirty data before this RBA has been fully written to the disk.

Note: When a checkpoint event occurs, the CKPT process records the address (RBA) of the redo log records written at that time. The recorded RBA is called checkpoint RBA, the dirty blocks in the buffer cache protected by logs from the last checkpoint RBA to the current checkpoint RBA will be written into the data file.

3.4 on-disk RBA

Definition: the address at the last position of the log file written by LGWR. Redo the last redo record of the log file in the disk.

Note: on disk rba is the end point of the Oracle rollback operation. As the name suggests, on disk means 'on disk. rba, which is higher than this one, is in the log buffer and has not been written into the log files on the disk. therefore, it cannot be used for restoration.

3.5 target RBA

Definition: checkpoint RBA at the end of a checkpoint event

Note: To shorten the instance recovery time, DBWn tries its best to set the checkpoint RBA target value to a long-term point.

1 2 Next Page