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Invalidate stale cache data
To reduce the window of time when clients may see stale data, you can use an event-based or programmatic invalidation mechanism.
Sparse and complete caches can be invalidated or updated using an event generator such as Java™ Message Service (JMS). Invalidation using JMS can be manually tied to any process that updates the back-end using a database trigger. A JMS ObjectGridEventListener plug-in is provided in eXtreme Scale that can notify clients when the server cache changes. This type of notification decreases the amount of time the client can see stale data.
Event-based invalidation normally consists of the following three components.
- Event queue: An event queue stores the data change events. It could be a JMS queue, a database, an in-memory FIFO queue, or any kind of manifest as long as it can manage the data change events.
- Event publisher: An event publisher publishes the data change events to the event queue. An event publisher is usually an application you create or an eXtreme Scale plug-in implementation. The event publisher knows when the data is changed or it changes the data itself. When a transaction commits, events are generated for the changed data and the event publisher publishes these events to the event queue.
- Event consumer: An event consumer consumes data change events. The event consumer is usually an application to ensure the target grid data is updated with the latest change from other grids. This event consumer interacts with the event queue to get the latest data change and applies the data changes in the target grid. The event consumers can use eXtreme Scale APIs to invalidate stale data or update the grid with the latest data.
For example, JMSObjectGridEventListener has an option for a client-server model, in which the event queue is a designated JMS destination. All server processes are event publishers. When a transaction commits, the server gets the data changes and publishes them to the designated JMS destination. All the client processes are event consumers. They receive the data changes from the designated JMS destination and apply the changes to the client's near cache.
See Enable client invalidation for more information.
The WebSphere eXtreme Scale APIs allow manual interaction of the near and server cache using the Session.beginNoWriteThrough(), ObjectMap.invalidate() and EntityManager.invalidate() API methods. If a client or server process no longer needs a portion of the data, the invalidate methods can be used to remove data from the near or server cache. The beginNoWriteThrough method applies any ObjectMap or EntityManager operation to the local cache without calling the loader. If invoked from a client, the operation applies only to the near cache (the remote loader is not invoked). If invoked on the server, the operation applies only to the server core cache without invoking the loader.
Use programmatic invalidation with other techniques to determine when to invalidate the data. For example, this invalidation method uses event-based invalidation mechanisms to receive the data change events, and then uses APIs to invalidate the stale data.
Parent topic:Database integration: Write-behind, in-line, and side caching
Sparse and complete cache
Side cache and in-line cache
Data pre-loading and warm-up
Database synchronization techniques