How Parsing Works



1. Include VPD predicates:   If Virtual Private Database (VPD, formerly known as row-level security) is in use and active for one of the tables referenced in the parsed SQL statement, the predicates generated by the security policies are included in its WHERE clause.

2. Check syntax, semantics, and access rights: This step makes sure not only that the SQL statement is correctly written but also that all objects referenced by the SQL statement exist and the user parsing it has the necessary privileges to access them.

3. Store parent cursor in a shared SQL area: Whenever a shareable parent cursor isn’t yet available, some memory is allocated from the library cache, and a new parent cursor is stored inside it.

4. Generate execution plan: During this phase, the query optimizer produces an execution plan for the parsed SQL statement.

5. Store child cursor in a shared SQL area: Some memory is allocated, and the shareable child cursor is stored inside it and associated with its parent cursor.