BCT reads additonal blocks and performance of backup gets worse (Doc ID 2636416.1)

Last updated on APRIL 17, 2023

Applies to:

Symptoms

When BCT (Block Change Tracking) is enabled, RMAN will only read changed blocks to include in the incremental backup.
However, if the lead blocks (*) of the datafiles have never been updated, the BCT will continuously read the updated blocks.

Due to this behavior, performance of incremental backup may get worse.

(*) lead blocks refers to the block whose block number is less than 983808 when using db_block_size=8k.

Changes

This problem may happen on following situation.

• BCT (Block Change Tracking) is enabled
• Lead blocks of datafile has never updated after getting incremental backup.

Cause

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