The store based cursor also handles cursors for non-persistent messages, which are not stored in the message store. By buffering to disk, it allows the message broker to handle message bursts from producers without resorting to paging in from slow storage: This type of cursor can be used when the message store might be relatively slow, but consumers are generally fast. When memory in the broker reaches its limit, it can page messages to temporary files on disk.

The File based Cursor is dervied from the VM Cursor. This can be very fast, but also has the downside of not being able to handle very slow consumers or consumers that have been inactive for a long time: File based Cursor

The VM Cursor is how ActiveMQ 4.x works: references to a message are held in memory, and passed to the dispatch queue when needed. There are two additional types of cursor that could be used: VM Cursor and File based Cursor, described below. The default message cursor type in ActiveMQ 5.0 is Store based. If a Consumer becomes active after messages are pending from the store for it, or it’s slower than the producer, then messages are paged in to the dispatch queue from a pending cursor: When Message Consumers are both active and fast - keeping up with the Message Producer This is a robust and very scalable approach, but not the most performant for cases when the consumer(s) can keep up with the producer(s) of messages.ĪctiveMQ 5.0 takes a hybrid approach, allowing messages to pass from producer to consumer directly (after the messages have been persisted), but switches back to using cursors if the consumer(s) fall behind. While a reference itself is not large, it does impose a limit on the maximum number of messages that can be pending delivery.Ī typical approach for messaging systems dispatching persistent messages is to pull them in batches from long term storage when a client is ready to consume them, using a cursor to maintain the next to dispatch position.

Releases prior to 5.0 kept references in memory for all the messages that could be dispatched to an active Durable Topic Consumer or a Queue. Features > Message Dispatching Features > Message Cursors Message CursorsĪ common problem in previous versions of ActiveMQ was running out of RAM buffer when using non-persistent messaging.īeginning with ActiveMQ 5.0.0, there is a new memory model that allows messages to be paged in from storage when space is available (using Store cursors for persistent messages).

Cursors types