Fault Tolerance
Multiple process instances of rvcache can cooperate for fault-tolerant service.
Fault tolerance protects rvcache service against hardware failures, process termination and segmentation of the local network.
In this configuration, two or more rvcache processes run on separate computers—usually on separate network segments. All cooperating processes listen for the same set of subjects, and store the current values of those subjects. Only one process (called the primary active process) actively sends the current values to new listeners. The remaining processes (called inactive backup processes) are inactive—unless they detect that the primary active process has failed. If the primary fails, one of the backup process activates in its place, restoring service automatically.
These sections describe fault tolerance concepts and parameters in detail:
| • | Fault Tolerance Concepts in . |
| • | Fault Tolerance Programming in . |
| • | Developing Fault-Tolerant Programs on in . |
For administrative details, see Fault Tolerance.
Usage
To run rvcache as a fault-tolerant service, start two or more rvcache processes. It is essential that all processes use identical parameters—with only one exception:
| • | The -store parameter specifies a file for persistent storage of the cache and configuration parameters. Member processes must not share this file. Each member must keep its own distinct cache file (we recommend storing it on a local disk). |
Duplicating the Cache State
To duplicate the cache state, copy the cache file (so each process starts with an identical copy). Avoid file inconsistencies that can arise when copying the file while rvcache is running.