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Smart Scan will not work with Inter-Block Chaining and Can cause Performance Degradation (Doc ID 2120974.1)

Last updated on JULY 22, 2020

Applies to:

Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Gen 1 Exadata Cloud at Customer (Oracle Exadata Database Cloud Machine) - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Oracle Database Backup Service - Version N/A and later
Information in this document applies to any platform.

Symptoms

Performance on Exadata may suddenly get worse and the amount of Smart Scan may reduce. You may see excessive "cell single block physical read" waits instead of the expected "cell smart table scan". This may be after new columns have been added to an existing table. 

Changes

 The change may be because of any activity which results in the row size increasing resulting in more inter-block chaining

Cause

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