3 tier Architecture

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 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 any 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