CREATE ASYNCEVENTLISTENER

See also Handling DML Events Asynchronously.

Syntax

CREATE ASYNCEVENTLISTENER listener-name
(
  LISTENERCLASS 'class-name'
  INITPARAMS 'init-params'
  [ MANUALSTART boolean-constant ]
  [ ENABLEBATCHCONFLATION boolean-constant ]
  [ BATCHSIZE integer-constant ]
  [ BATCHTIMEINTERVAL integer-constant ]
  [ ENABLEPERSISTENCE boolean-constant ]
  [ DISKSTORENAME  store-name]
  [ MAXQUEUEMEMORY integer-constant ]
  [ ALERTTHRESHOLD integer-constant ]
)
  SERVER GROUPS ( server_group_name [, server_group_name ]*)

LISTENERCLASS

The fully-qualified name of the class that implements the AsyncEventListener interface. For example, "user.application.TestAsyncEventListener". If you are configuring the built-in DBSynchronizer implementation, specify com.pivotal.gemfirexd.callbacks.DBSynchronizer.

INITPARAMS

Specify initialization parameters to pass to the init() method of the AsyncEventListener implementation.

GemFire XD passes a single string of initialization parameters when you execute the CREATE ASYNCEVENTLISTENER statement. You must include the INITPARAMS argument, even if it defines no parameters (INITPARAMS '').

As a best practice, Pivotal recommends that you supply only a single parameter in the string using the format file=path-to-file, where path-to-file references a file that defines each listener parameter on a dedicated line, similar to:

user=user-name
password=plain-text-password

Using a separate parameter file enables you to change initialization parameters after you have configured the listener in GemFire XD. Only the file path is hard-coded in the listener configuration. If you define parameters in the string passed to INITPARAMS, then you must drop and re-create the listener in order to change any of those parameter values.

If you send user credentials in the initialization parameters, consider encrypting the password using encrypt-password with the external option. Your listener will need to use the AsyncEventHelper.decryptPassword method to decrypt the password before sending credentials to the outside data source.

The built-in DBSynchronizer implementation requires specific parameters in order to initiate a connection to a JDBC data source and apply DML to a database. See DBSynchronizer Initialization Parameters for a complete reference to the DBSynchronizer parameters.

MANUALSTART

A boolean value that specifies whether you need to manually start the listener with SYS.START_ASYNC_EVENT_LISTENER. If you do not supply a value, the default is "true" and you must start the listener manually using SYS.START_ASYNC_EVENT_LISTENER.

ENABLEBATCHCONFLATION

A Boolean value that determines whether GemFire XD should conflate messages. The default is false.

BATCHSIZE

GemFire XD creates an internal queue where it stores the events that are eventually dispatched to a configured listener. Multiple events are dispatched to the listener in batches, and the BATCHSIZE parameter defines the maximum number of messages that a batch can contain. The default is 100 messages. This parameter, along with BATCHTIMEINTERVAL, determine the frequency with which GemFire XD dispatches queued events.

BATCHTIMEINTERVAL

The maximum number of milliseconds that can elapse between sending batches. The default is 1000 milliseconds.

ENABLEPERSISTENCE

A Boolean value that determines whether GemFire XD persists the event queue to disk for high availability. The default is "False."

Note: GemFire XD uses disk storage for queue overflow when needed, even if you do not enable persistence for the queue.

DISKSTORENAME

The named disk store to use for storing the queue overflow (default), or for persisting the queue. If you specify a value, the named disk store must exist. If do not specify a value, GemFire XD uses the default disk store for queue overflow and persistence.

MAXQUEUEMEMORY

The maximum amount of memory in megabytes that the queue can consume before overflowing to disk. The default is 100 megabytes.

ALERTTHRESHOLD

The maximum number of milliseconds that an event can remain in this queue before GemFire XD logs an alert. The default is value is "0."

SERVER GROUPS

A comma-separated list of server group names. GemFire XD deploys the event listener implementation on all peers in the specified server group(s).

Note: The specified server groups must contain at least one data store member at the time you execute the CREATE ASYNCEVENTLISTENER statement.

Note: When you deploy an event listener (or DBSynchronizer) to listen for asynchronous events, specify a server group that contains no more than 3 data stores. GemFire XD automatically designates the first listener to startup as the "primary," and the remaining listeners become "secondaries." Every additional "secondary" can slow down the publisher. By default all GemFire XD members that store data are members of a single "default" server group.

When multiple data stores host an event listener, there is no direct way to ensure that a specific GemFire XD data store hosts the active instance. If you require a specific member to host the active instance, ensure that only that member is running in the target server groups when you deploy the listener and attach the table. You can then start the remaining data stores in the server group, and they will host redundant, standby instances.