ColdFusion Developer's Guide

Beta Beta Beta Beta Beta Beta Beta Beta Beta Beta
About client and session variables
ColdFusion provides two tools for managing the client state: client variables and session
variables. Both types of variables are associated with a specific client, but you manage and use
them differently, as described in the following table:
Variable type Description
Client Data is saved as cookies, database entries, or Registry entries. Data is
saved between server restarts, but is initially accessed and saved more
slowly than data stored in memory.
Each type of data storage has its own time-out period. You can specify the
database and Registry data time-outs in ColdFusion Administrator.
ColdFusion sets Cookie client variables to expire after approximately 10
years.
Data is stored on a per-user and per-application basis. For example, if you
store client variables as cookies, the user has a separate cookie for each
ColdFusion application provided by a server.
Client variables must be simple variables, such as numbers, dates, or
strings. They cannot be arrays, structures, query objects, or other objects.
Client variable names can include periods. For example, My.ClientVar is a
valid name for a simple client variable. Avoid such names, however, to
ensure code clarity.
You do not have to prefix client variables with the scope name when you
reference them, However, if you do not use the Client prefix, you might
unintentionally refer to a variable with the same name in another scope.
Using the prefix also optimizes performance and increases program
clarity.
You do not lock code that uses client variables.
You can use client variables that are stored in cookies or a common
database in clustered systems.
Session Data is stored in memory so it is accessed quickly.
Data is lost when the client browser is inactive for a time-out period. You
specify the time-out in the ColdFusion Administrator, the Application.cfc
initialization code, or Application.cfm.
As with client variables, data is available to a single client and application
only.
Variables can store any ColdFusion data type.
You must prefix all variable names with the Session scope name.
Lock code that uses session variables to prevent race conditions.
You can use session variables in clustered systems only if the systems
support “sticky” sessions, where a session is limited to a single server.
404 Using Persistent Data and Locking