Queue Type | Description |
Reliable | Reliable queues have their messages stored in the Universal Messaging realm's own memory space. The first fact that is implied is that the maximum number of bytes that all messages across all Reliable queues within a Universal Messaging realm is limited by the maximum heap size available to the Java Virtual Machine hosting that realm. The second fact implied is that if the Universal Messaging realm is restarted for any reason, all messages stored on Reliable queues will be removed from the queue as a matter of policy. However, as Universal Messaging guarantees not to ever reuse event IDs within a queue, new messages published in those queues will get assigned event IDs incremented from the event ID of the last message prior to the previous instance stopping. |
Persistent | Persistent queues have their messages stored in the Universal Messaging realm's persistent queue disk-based store. The persistent queue store is a high performance file-based store that uses one or more files for each queue on that realm, thus facilitating migrating whole queues to different realms. For information about setting up a multi-file disk store for persistent channels or persistent queues, see the section
Multi-File Disk Stores. All messages published to a Persistent queue will be stored to disk, hence it is guaranteed that they will be kept and delivered to subscribers until it is purged or removed as a result of a "Time to Live" (TTL) or capacity policy. Messages purged from a Persistent queue are marked as deleted, however the store size will not be reduced immediately. If the store is backed by a single file, the store size will not be reduced until maintenance is performed on the queue using the Enterprise Manager or an Administration API call, or when auto-maintenance is triggered. Stores backed by multiple files will be cleaned up through the removal of individual files, according to the conditions described in the section
Multi-File Disk Stores. This augments the high performance of the Universal Messaging realm. |
Mixed | Mixed queues allow users to specify whether the event is stored persistently or in memory, as well as the "Time To Live" (TTL) of the individual event. On construction of a Mixed queue, the TTL and Capacity can be set, and if the user supplies a TTL for an event this is used instead of the queue. Events stored persistently are either stored on a single file or on multiple files in the same manner as a Persistent queue. |