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12. Before Oracle makes the update, information about the old state of the blocks is recorded in a rollback segment and the original version of the values is also recorded in the redo buffers cache.
13. Oracle updates the rows and records the new version of the values in the redo buffer cache in the SGA.
14. The user issues the COMMIT command to make the change permanent to the database.
15. Oracle records an entry indicating a commit in the redo buffer cache, and the old, new, and the commit entry are all flushed down to the online redo log (whichever one is the current one in use).
16. The rollback segment is released (but not overwritten) for other processes to use.
17. Oracle releases the locks on the table.
18. The user receives a commit successful message. (The exact wording of this message varies from tool to tool.)
19. If the user issues a rollback instead of a commit, the old versions of the values changed are restored back to the Oracle data blocks from the rollback segment. Oracle also writes to the redo buffer cache an entry indicating that a rollback was performed.

Summary

This chapter covered the major parts of the Oracle architecturethe architecture used by all the tools and commands against the database. Even though familiarity with the intricate workings of the architecture is not necessary for you to use the database and tools, it provides valuable background information in helping to work out why the database is not functioning as it should. Knowledge of the architecture also lends more meaning to some of the more cryptic error and information messages.

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