Technical Design

There are several technical design decisions for configurable behavior.

Initial provisioning

If a new member joins, there are two ways you can handle the initial provisioning that is executed to replicate all existing values to the new member.

First, you can have an async fill up, which does not block reads while the fill up operation is underway. That way, you have immediate access on the new member, but it will take time until all values are eventually accessible. Not yet replicated values are returned as non-existing (null). Write operations to already existing keys during this async phase can be lost, since the vector clock for an entry might not be initialized by another member yet, and it might be seen as an old update by other members.

Second, you can perform a synchronous initial fill up, which blocks every read or write access to the map until the fill up operation is finished. Use this way with caution since it might block your application from operating.

Replication delay

By default, the replication of values is delayed by 100 milliseconds when no current waiting replication is found. This collects multiple updates and minimizes the operations overhead on replication. A hard limit of 1000 replications is built into the system to prevent OutOfMemory situations where you put lots of data into the replicated map in a very short time. The delay is configurable. A value of "0" means immediate replication. You can configure the trade off between replication overhead and the time for the value to be replicated.

Concurrency Level

The concurrency level configuration defines the number of mutexes and segments inside the replicated map storage. A mutex/segment is chosen by calculating the hashCode of the key and using the module by the concurrency level. If multiple keys fall into the same mutex, they will wait for other mutex holders on the same mutex to finish their operation.

For a high amount of values, or for high contention on the mutexes, this value can be changed.