User Guide

Managing the client state 343
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:
Session variables are normally better than client variables for values that need to exist for only a
single browser session. You should reserve client variables for client-specific data, such as client
preferences that you want available for multiple browser sessions.
Maintaining client identity
Because the web is a stateless system, client management requires some method for maintaining
knowledge of the client between requests. Normally you do this using cookies, but you can also
do it by passing information between application pages. The following sections describe how
ColdFusion maintains client identity in a variety of configurations and environments, and discuss
issues that can arise with client state management.
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 MX 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 MX 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.