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Enabling content-based filtering with publish/subscribe
WebSphere® MQ provides the ability to specify a filter when a subscription is made, but this can only refer to items in headers. WebSphere Message Broker can act as a content filtering provider for WebSphere MQ, and so allows extended filters to be specified by subscribers that can refer to elements in the body of publications.
Content filtering must be enabled in the broker for this service to be available to WebSphere MQ subscribers.
Before you start
- Read about Selectors on WebSphere MQ.
- Read the following overview of how WebSphere MQ selects content of messages.
When an application publishes on a topic string, where one or more subscribers have a selection string selecting on the content of the message, WebSphere MQ requests that the extended message selection provider parse the publication and inform WebSphere MQ whether the publication matches the selection criteria specified by each subscriber with a content filter.
If the extended message selection provider determines that the publication matches the subscriber's selection string, the message continues to be delivered to the subscriber.
If the extended message selection provider determines that the publication does not match, the message is not delivered to the subscriber. This might cause the WebSphere MQ MQPUT or MQPUT1 call to fail with reason code MQRC_PUBLICATION_FAILURE. If the extended message selection provider is unable to parse the publication, reason code MQRC_CONTENT_ERROR is returned and the MQPUT or MQPUT1 call fails.
If the extended message selection provider is unavailable or is unable to determine whether the subscriber should receive the publication, reason code MQRC_SELECTION_NOT_AVAILABLE is returned and theWebSphere MQ MQPUT or MQPUT1 call fails.
When a subscription is being created with a content filter and the extended message selection provider is not available, the WebSphere MQ MQSUB call fails with reason code MQRC_SELECTION_NOT_AVAILABLE. If a subscription with a content filter is being resumed and the extended message selection provider is not available, the WebSphere MQ MQSUB call returns a warning of MQRC_SELECTION_NOT_AVAILABLE, but the subscription is allowed to be resumed.
- Each queue manager that supports Extended Message Selection (Content Based Filtering), requires a broker that is associated with it and Content Based Filtering enabled on at least one execution group. If a client subscribes and specifies a content-based filtering expression against a queue manager that does not have this function enabled, it receives MQRC_SELECTION_NOT_AVAILABLE on the subscription request.
For z/OS® systems, verify that the message broker started task ID has UPDATE access permission to profile <MQ_QMNAME>.BATCH of class MQCONN.
On Linux, UNIX and Windows systems, grant authorization for the system to the queue manager: setmqaut -t <qmgr> +system -p <brokerUserId>
WebSphere Message Broker extends the message selection support provided by WebSphere MQ. WebSphere Message Broker does this by allowing ESQL statements rather than SQL92 statements, and filtering based on message content. See Content based filtering using ESQL for details of the scope and exclusions of supported ESQL.
- Content based filtering is no longer limited to WebSphere MQ MQRFH2 subscribers. WebSphere Message
Broker provides content filtering
services for the following WebSphere MQ subscribers:
- MQRFH2
- MQSUB
If you are performing content filtering based on the NameValueData field, within an MQRFH2 header, on z/OS, the data can be present either in the first or second MQRFH2 header. For example, the filter:
might not work as you expect on z/OS. Use the following syntax to search all MQRFH2 headers:Root.MQRFH2.mcd.Msd='XML'
FOR ANY Root.MQRFH2[] AS I (I.mcd.Msd='XML')
- WebSphere MQ message properties are supported as part of the filter expression.
- If the publication does not contain an mcd folder, the payload is assumed to be XMLNSC.
Read the following steps to see how to enable content-based filtering on WebSphere Message Broker.