WebSphere Message Brokers
File: ak04895_
Writer: John Prowse

Reference topic

This build: July 31, 2007 21:31:20

ESQL variables

Types of variable

You can use the DECLARE statement to define three types of variable:
External
External variables (defined with the EXTERNAL keyword) are also known as user-defined properties (see User-defined properties in ESQL). They exist for the entire lifetime of a message flow and are visible to all messages passing through the flow. You can define external variables only at the module and schema level. You can modify their initial values (optionally set by the DECLARE statement) at design time, using the Message Flow editor, or at deployment time, using the BAR editor. You cannot later modify their values using ESQL.
Normal
"Normal" variables have a lifetime of just one message passing through a node. They are visible to that message only. To define a "normal" variable, omit both the EXTERNAL and SHARED keywords.
Shared
Shared variables can be used to implement an in-memory cache in the message flow (see Optimizing message flow response times). Shared variables have a long lifetime and are visible to multiple messages passing through a flow (see Long-lived variables). They exist for the lifetime of the execution group process, the lifetime of the flow or node, or the lifetime of the node’s SQL that declares the variable (whichever is the shortest). They are initialized when the first message passes through the flow or node after each broker startup.

See also the ATOMIC option of the BEGIN ... END statement. The BEGIN ATOMIC construct is useful when a number of changes need to be made to a shared variable and it is important to prevent other instances seeing the intermediate states of the data.

Related concepts
ESQL overview
ESQL variables
User-defined properties in ESQL
Long-lived variables
Related tasks
Developing ESQL
Related reference
DECLARE statement
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This build: July 31, 2007 21:31:20

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