Types of Parallel Database Architecture
Shared memory system
Advantages of Shared memory system
- Shared memory system uses multiple processors which is attached to a global shared memory via intercommunication channel or communication bus.
- Shared memory system have large amount of cache memory at each processors, so referencing of the shared memory is avoided.
- If a processor performs a write operation to memory location, the data should be updated or removed from that location.
Disadvantages of Shared memory system
- Data is easily accessible to any processor.
- One processor can send message to other efficiently.
- Waiting time of processors is increased due to more number of processors.
- Bandwidth problem.
Shared Disk System
Advantages of Shared Disk System
- Shared disk system uses multiple processors which are accessible to multiple disks via intercommunication channel and every processor has local memory.
- Each processor has its own memory so the data sharing is efficient.
- The system built around this system are called as clusters.
Disadvantage of Shared Disk System
- Fault tolerance is achieved using shared disk system.
Fault tolerance: If a processor or its memory fails, the other processor can complete the task. This is called as fault tolerance.
Applications of Shared Disk System
Digital Equipment Corporation(DEC):
- Shared disk system has limited scalability as large amount of data travels through the interconnection channel.
- If more processors are added the existing processors are slowed down.
DEC cluster running relational databases use the shared disk system and now owned by Oracle.
Shared nothing disk system
Advantages of Shared nothing disk system
- Each processor in the shared nothing system has its own local memory and local disk.
- Processors can communicate with each other through intercommunication channel.
- Any processor can act as a server to serve the data which is stored on local disk.
Disadvantages of Shared nothing disk system
- Number of processors and disk can be connected as per the requirement in share nothing disk system.
- Shared nothing disk system can support for many processor, which makes the system more scalable.
Applications of Shared nothing disk system
- Data partitioning is required in shared nothing disk system.
- Cost of communication for accessing local disk is much higher.
- Tera data database machine.
- The Grace and Gamma research prototypes.
Hierarchical System or Non-Uniform Memory Architecture
Advantages of NUMA
- Hierarchical model system is a hybrid of shared memory system, shared disk system and shared nothing system.
- Hierarchical model is also known as Non-Uniform Memory Architecture (NUMA).
- In this system each group of processor has a local memory. But processors from other groups can access memory which is associated with the other group in coherent.
- NUMA uses local and remote memory(Memory from other group), hence it will take longer time to communicate with each other.
Disadvantages of NUMA
- Improves the scalability of the system.
- Memory bottleneck(shortage of memory) problem is minimized in this architecture.
The cost of the architecture is higher compared to other architectures.