4.2. Soft state
In soft state database provides a relaxed view of data in terms of consistency. Information on soft state will expire if it is not refreshed. The value stored in soft state may not be up-to-date, but handy for approximations. Soft state data are in changing state over time without user intervention and/or input due to eventual
consistency.
The soft state layer is responsible for .
• Client interface.
• Data partitioning.
• Caching.
• Concurrency control.
• High level processing.
Replicating soft state provides applications with two critical
capabilities:
• Rapid failover to other instances during crashes.
• Fine-grained load-balancing across instances to prevent overload .
Soft state is useful for efficiency because of the eventual consistency model such as short-lived user sessions, stored aggregates and transformations on large datasets and general purpose write-through caches for files and database records.
Whilst soft state is lost or made unavailable due to service instance crashes and overloads, reconstructing it through user interaction or third-tier re-access can be expensive in terms of time and resources . User can afford database to be consistent over time by synchronizing information between different database nodes. They can Cache data (soft state) and use it later to increase the database response time. They may be having a number of database nodes with distributed data to be highly available (partition tolerance).