How Distribution Works

To use distributed and replicated regions, you should understand how they work and your options for managing them.

Note: The management of replicated and distributed regions supplements the general information for managing data regions provided in Basic Configuration and Programming. See also org.apache.geode.cache.PartitionAttributes.

A distributed region automatically sends entry value updates to remote caches and receives updates from them.

Distributed entry updates come from the Region put and create operations (the creation of an entry with a non-null value is seen as an update by remote caches that already have the entry key). Entry updates are distributed selectively - only to caches where the entry key is already defined. This provides a pull model of distribution, compared to the push model that you get with replication.
Distribution alone does not cause new entries to be copied from remote caches.
A distributed region shares cache loader and cache writer application event handler plug-ins across the cluster.

In a distributed region, new and updated entry values are automatically distributed to remote caches that already have the entries defined.

Step 1: The application updates or creates the entry. At this point, the entry in the M1 cache may not yet exist.

Application updating or creating entry X1 in Distributed Region A on Member 1 (M1). No entry in Distributed Region A on Member 2 (M2)

Step 2: The new value is automatically distributed to caches holding the entry.

X1 automatically distributed to Distributed Region A on Member 2 (M2)

Step 3: The entry’s value is the same throughout the cluster.

X1 present in Distributed Region A on Member 1 (M2) and Member 2 (M2)