MACROMEDIA COLDFUSION 4.5-CFML LANGUAGE, Reference

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124 CFML Language Reference
following table shows which features are available for Server, Application, and Session
scope.
Each feature that you select has tradeoffs.
•
No automatic checking or locking. If you select this button, no reads or writes
are locked or checked for correct protection. You should select this only after
you have run with full checking and know that there are no errors to handle and
that all locking is handled programmatically. Selecting this button provides the
fastest performance.
•
Full checking. If you select this button, all unlocked accesses will be detected.
You should select this when you are in debug mode. Selecting this button slows
performance.
•
Automatic read locking. If you select this button, all reads are locked and
unlocked writes cause an error. Selecting this button also slows down
performance considerably.
•
Single-threaded sessions: If you select this button, the whole request has to
finish before another request for the same session is processed. Selecting this
button may have an effect on performance depending on the request pattern.
For example, the total response time may increase if an application has
multiple frames that can be refreshed at once, thus causing multiple requests to
have to queue up and wait to be processed.
For an analysis of best practices with respect to locking, please refer to Administering
ColdFusion Server.
Deadlocks
CFLOCK uses kernel level synchronization objects that are released automatically
upon timeout and/or abnormal termination of the thread that owns them. Therefore,
ColdFusion will never deadlock for an infinite period of time while processing a
CFLOCK tag. However, very large timeouts can block request threads for long periods
of time and thus radically decrease throughput. Always use the minimum timeout
value allowed.
Another cause of blocked request threads is inconsistent nesting of CFLOCK tags and
inconsistent naming of locks. If you are nesting locks, you and everyone accessing the
locked variables must consistently nest CFLOCK tags in the same order . If everyone
accessing locked variables does not adhere to these conventions, a deadlock can occur.
A deadlock is a state in which no request can execute the locked section of the page.
Features Server Application Session
No automatic checking or locking Yes Yes Yes
Full checking Yes Yes Yes
Automatic read locking Yes Yes Yes
Single Threaded Sessions Yes