Although
lock escalation reduces the number of locks the lock manager process has to
handle, this escalation causes unaffected rows to be locked. With Oracle, the
lock indicator is stored within the data block itself, so there is no increase in
overhead for a lock manager when the number of locks increases. Consequently,
there is never any need for Oracle to escalate a lock.
A lock manager called the Distributed Lock Manager (DLM) has historically been
used with Oracle Parallel Server to track locks across multiple instances of Oracle.
This is a completely different and separate locking scheme that doesn??™t affect the way
Oracle handles row locks. The DLM technology used in Oracle Parallel Server was
improved and integrated into a core product in Oracle9i, Real Application Clusters.
Real Application Clusters are described in more detail in Chapter 9.
194 | Chapter 8: Oracle Multiuser Concurrency
How Oracle Handles Locking
If you??™ve read this chapter from the beginning, you should now know enough about
the concepts of concurrency and the features of Oracle to understand how the Oracle
database handles multiuser access.
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