Fleet
is a middleware system
implementing a distributed repository for persistent objects resilient
to malicious failures. It is built on top of quorum system techniques
to enhance the performance of the systems, such as reduce the access
cost per operation and the load balance of the systems, and improve the
system scalability. Fleet is primarily target for
supporting highly critical applications: in particular the objects it
stores
maintain the correct semantics despite the arbitrary failure (including
hostile
corruption) of a limited number of Fleet servers. It is designed to be
highly
available, dynamically extensible with new object types and highly
scalable to
large numbers of servers and clients. Below are sketched some of its
features:
- Fault tolerance: the
correctness of the services provided and the semantics of the object stored is guaranteed
despite any benign failures and a limited number of Byzantine server
failures.
- Fault detection: Fleet
continually monitors servers to detect when the number of faulty servers is approaching that
tolerable limit
- High scalability: this
is achieved by means of quorum system techniques. This resulted also in a better load balancing
across servers and lower access cost.
- Concurrent semantics:
Fleet provides a generic protocol for turning any object into a shared
object with linearizable concurrent semantics,
in addition to protocols for implementing safe and atomic varibles.
- Extensibility: Fleet provide a mechanism to turn at run-time any application-defined
object into Fleet objects, and which is completely transparent to the
user.
- Liveness: during periods of stability operations between clients and
servers terminate with probability one.
- Autonomy: each Fleet object
is replicated at a set of Fleet servers designed by the application
depending on the level of fault-tolerance desired by the creator of the
object.
- Isolation: to support
possible overlapping universes of Fleet servers, each Fleet Object is
created with a name space and that allows only the creator of the name
space to place new object within it.