Types of Parallel Database Architecture

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.
shared memory system

Advantages of Shared memory system
  • Data is easily accessible to any processor.
  • One processor can send message to other efficiently.
Disadvantages of Shared memory system
  • Waiting time of processors is increased due to more number of processors.
  • Bandwidth problem.

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.
shared disk memory
Advantages 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.
Disadvantage of Shared Disk System
  • 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.
Applications of Shared Disk System
Digital Equipment Corporation(DEC): DEC cluster running relational databases use the shared disk system and now owned by Oracle.

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.
shared nothing disk system

Advantages 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.
Disadvantages of Shared nothing disk system
  • Data partitioning is required in shared nothing disk system.
  • Cost of communication for accessing local disk is much higher.
Applications of Shared nothing disk system
  • Tera data database machine.
  • The Grace and Gamma research prototypes.

Hierarchical System or Non-Uniform Memory Architecture

  • 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.
Advantages of NUMA
  • Improves the scalability of the system.
  • Memory bottleneck(shortage of memory) problem is minimized in this architecture.
Disadvantages of NUMA
The cost of the architecture is higher compared to other architectures.