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By default, when flow control is disabled and the relevant memory limit is reached, the slow consumer's messages are backed up in a temporary file. An alternative strategy for coping with the excess messages, however, is simply to discard the slow consumer's messages when they exceed a certain limit (where the oldest messages are discarded first). This strategy avoids the overhead of writing to a temporary file.

For example, if the slow consumer is receiving a feed of real-time stock quotes, it might be acceptable to discard older, undelivered stock quotes, because the information becomes stale.

To enable discarding of messages, define a pending message limit strategy in the broker configuration. For example, to specify that the backlog of messages stored in the broker (not including the prefetched messages) cannot exceed 10 for any topics that match the PRICES.> pattern (that is, topic names prefixed by PRICES.), configure the broker as follows:

<beans ... >
  <broker ...>
    <!--  lets define the dispatch policy -->
          <policyEntry topic="PRICES.>">

            <!-- lets force old messages to be discarded for slow consumers -->
              <constantPendingMessageLimitStrategy limit="10"/>


For more details about how to configure pending message limit strategies, see

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