Oracle has many features that contribute to OLTP performance, reliability, scalability, and availability. This section presents the basic attributes of many of these features. This section is by no means exhaustive; it’s only intended to be an introduction. Please see your relevant Oracle documentation and third-party books for more information.
As discussed in Chapter 7, Oracle has implemented excellent support for concurrency and performance in OLTP systems. Some of the key features relevant to OLTP are as follows:
Oracle locks only the rows a transaction works on and never escalates these locks to page-level or table-level locks. This prevents any false lock contention for cases in which users want to work on different rows but contend for locks that have escalated to higher granularity levels, such as page locks.
Oracle provides statement-level and transaction-level data consistency without requiring read locks. A query is guaranteed to see only the data that was committed at the time the query started. The changes made by transactions that were in-flight but uncommitted at the time the query started won’t be visible. Transactions that began after the query started and were committed before the query finishes also won’t be seen by the query. Oracle uses rollback segments to reproduce the data as it existed at the time the query started. This capability avoids ...