3 tier Architecture

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4 tier Architecture

We can add ‘n’ no.of architectures  

Library cache performs

• Syntactical checking & whether SQL statement is valid or not like expressions messing from ok
• Semantically checking whether the user is valid or not checks the privileges.
• Data dictionary cache checks in base tables whether the table is available or not if available then the optimizer the oracle brain] checks whether the table has an index or not then the DDC makes an execution plan. 

IF there is any update Then DBWR does 3 things i) updating db files ii) updating redo log files iii) updating index files    

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