ESQL variables
ESQL variables can be described
as external variables, normal variables,
or shared variables; their use is defined in the DECLARE
statement.
ESQL variable names
You can use only names
that conform to the rules of ESQL. That is, the names can contain
only alphanumeric characters (including underscore), the first character
cannot be numeric, and names must be at least one character long.
You can avoid these limitations by enclosing names that do not conform
to these rules in double quotation marks.
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 that pass 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) by using the Message
Flow editor, or at deployment time, by using the Broker Archive editor.
You can query and set the values of user-defined properties
at run time by using the IBM® Integration
API (also
known as the CMP). For
more information, see Setting message flow user-defined properties at run time in a CMP application.
- 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 (defined with the SHARED keyword)
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 that pass through
the flow; see Long-lived variables. They exist for the
lifetime of the integration server 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 have to be made to a shared variable and
when it is important to prevent other instances seeing the intermediate
states of the data.
Last updated Friday, 21 July 2017