Oracle Essentials: Oracle9i, Oracle8i and Oracle8, Second Edition

Concurrent Access and Performance

When you read through all the steps involved in the above processes, it seems as though Oracle would be a very slow database. This is not at all true. Oracle has consistently turned in benchmarks that make it one of the fastest databases, if not the fastest, on the market today.

Oracle provides good performance while implementing multiversion read consistency by minimizing and deferring unnecessary I/O operations. To assure the integrity of the data in a database, the database must be able to recover in the event of a system failure. This means that there must be a way to ensure that the data in the database accurately reflects the state of the committed data at the time of the crash. Oracle can do this by writing changed data to the database whenever a transaction commits. However, the redo log contains much less information than the entire data block for the changed data, so it’s much “cheaper” to write to disk. Oracle writes the redo information to disk as soon as a transaction commits and defers writing the changed data blocks to the database until several sets of changed blocks can be written together. Oracle can restore the database using the redo logs, and these procedures cut down on time-consuming I/O operations.

However, when you’re considering the performance of a database, you have to think about more than simple I/O operations. It doesn’t really matter how fast your database runs if your transaction is waiting for another transaction ...