[AMQ 7] How does the global-max-size attribute work?

Solution Verified - Updated -

Environment

  • Red Hat AMQ (AMQ)
    • 7.x

Issue

  • How does the paging mechanism work if I have configured the global-max-size attribute?

Resolution

The global-max-size attribute would make the message broker consider the cumulative total of messages across all configured addresses. This means if you have set global-max-size at 400Mb and deployed four 'addresses', A, B, C and D; the message broker would start paging on all four addresses when the size of A + B + C + D reach the 400Mb mark.

The downside of relying on global-max-size attribute is, the destinations with lower message volumes would also start to page messages. For example, let's assume you have configured 400Mb for the global-max-size attribute and the address A has 200Mb of messages, address B has 100Mb of messages, C has 50Mb of messages and D has 50Mb of messages. In this case, the cumulative total of the messages has reached 400Mb, thus, the message broker would start paging messages for all four destinations although addresses C and D have a lower volume of messages. Therefore, the use of global-max-size might not appropriate if the configured addresses aren't filling with messages equally. In such situations, configuring max-size-bytes value at each address can be considered the appropriate approach. The following formula can be used to configure max-size-bytes attribute per each address.

Message Broker's Java Heap * 75/100 > (number of destinations * max-size-bytes)  + [global-max-size]

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