Learn Oracle’s Hidden Kernel Subsystem Designators

While I have published direction on how to read an AWR report, the Oracle AWR and STATSPACK report often contain undocumented references to internal kernel parameters:

• calls to get snapshot scn: kcmgss

• calls to kcmgas

• calls to kcmgcs

• cleanout - number of ktugct calls

• enqueue hash chains  ksqrcl  

I created the Ion for Oracle product to parse through the complexities of a AWR report and filter-out the important metrics, but these internal kernel parameters are not directly documented by Oracle.

Below are the common prefixes for the Oracle kernel subsystems and their purpose.

As we can see, the kcmgas subsystem relates to Oracle’s kernel cache software, and ktugct is part of Oracle’s kernel transaction layer:

Oracle kernel abbreviations:

• K2 - Distributed Execution Layer for two-phase commit handling

• KA - Access Layer

• KC - Cache Layer

• KD - Data Layer

• KG - Generic Layer

• KJ - Lock Manager Layer

• KK - Compilation Layer – to parse SQL & compile PL/SQL

• KQ - Query Layer

• KS - Services Layer

• KT - Transaction Layer

• KV - Kernel Variables (eg. x$KVIS and X$KVII)

• KX - Execution Layer - Bind and execute SQL and PL/SQL

• KZ - Security Layer - Validate privs

• NPI - Network Program Interface

• ODS - Operating System Dependencies

• OPI - Oracle Program Interface

• RPI - Recursive Program Interface

• S - Operating System Dependencies

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