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Chapter 26. Handling Slow Consumers
A slow consumer with a server-side queue can pose a significant problem for server performance. As messages build up in the consumer’s server-side queue, memory usage will increase. Consequently, the server may enter paging mode which can impact performance. Criteria can be set, however, so that consumers that do not acknowledge messages quickly enough can be disconnected from the server. In the case of a non-durable JMS subscriber, this means the server would remove the subscription and all of its messages, freeing up valuable server resources.
The calculation to determine whether or not a consumer is slow inspects only the number of messages that a particular consumer has acknowledged. It does not take into account whether flow control has been enabled on the consumer, or whether the consumer is streaming a large message, for example. Keep this in mind when configuring slow consumer detection.
Slow consumer checks are performed using the scheduled thread pool. Each queue on the server with slow consumer detection enabled will cause a new entry in the internal java.util.concurrent.ScheduledThreadPoolExecutor instance. If there are a high number of queues and the slow-consumer-check-period is relatively low, then there may be delays in executing some of the checks. However, this will not impact the accuracy of the calculations used by the detection algorithm. See Thread Management for more details about this thread pool.
Slow consumer handling is on a per address-setting basis. See Address Settings for more information on configuring an address-setting, and refer to the appendix for the list of address-setting attributes. There are three attributes used to configure the handling of slow consumers. They are:
- slow-consumer-check-period
-
How often to check, in seconds, for slow consumers. The default is
5. - slow-consumer-policy
Determines what happens when a slow consumer is identified. The valid options are
KILLorNOTIFY:-
KILLwill kill the consumer’s connection, which will impact any client threads using that same connection. -
NOTIFYwill send aCONSUMER_SLOWmanagement notification to the client.
The default is
NOTIFY.-
- slow-consumer-threshold
-
The minimum rate of message consumption allowed before a consumer is considered slow. The default is
-1, which is unbounded.
Use the management CLI to read the current values for any of the attributes. For example, use the following command to read the current slow-consumer-policy for the address-setting with the name myAddress.
/subsystem=messaging-activemq/server=default/address-setting=myAddress:read-attribute(name=slow-consumer-policy)
Likewise, use the following example to set the same slow-consumer-policy.
/subsystem=messaging-activemq/server=default/address-setting=myAddress:write-attribute(name=slow-consumer-policy,value=<NEW_VALUE>)
