Interquery and Intraquery Parallelism in Parallel Database



Inter-query Parallelism

It is a form of parallelism where many different Queries or Transactions are executed in parallel with one another on many processors.

Advantages

It increases Transaction Throughput. That is, number of transactions executed in a given time can be increased.
It scales up the Transaction processing system. Hence, best suited for On-Line Transaction Processing (OLTP) systems.

Supported Parallel Database Architectures

It is easy to implement in Shared Memory Parallel System. Lock tables and Log information are maintained in the same memory. Hence, it is easy to handle those transactions which shares locks with other transactions. Locking and logging can be done efficiently.
In other parallel architectures like Shared Disk and Shared Nothing, the locking and logging must be done through message passing between processors, which is considered as costly operation when compared Shared Memory Parallel architecture. Cache coherency problem would occur.

Example Database systems which support Inter-query Parallelism

Oracle 8 and Oracle Rdb

Intra-Query Parallelism

It is the form of parallelism where Single Query is executed in parallel on many processors.

Advantages

To speed up a single complex long running queries.
Best suited for complex scientific calculations (queries).

Supported Parallel Database Architectures

SharedMemory, Shared Disk and Shared Nothing parallel architectures are supported. We need not worry about locking and logging as because it involves parallelizing single query.


Types

Intra-operation parallelism – the process of speeding up a query through parallelizing the execution of individual operations. The operations which can be parallelized are Sort, Join, Projection, Selection and so on.
Inter-operation parallelism – the process of speeding up a query through parallelizing various  operations which are part of the query. For example, a query which involves join of 4 tables can be executed in parallel in two processors in such a way that each processor shall join two relations locally and the result1 and result2 can be joined further to produce the final result.

Example Database systems which support Intra-query Parallelism

Informix, Terradata




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4 comments:

  1. Sir any example for Inter-query parallelism

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    Replies
    1. Inter-query parallelism is about executing different queries in different processors. For example, if we have two processors, execute one query in one processor and the other query in the other processor concurrently.

      Delete
  2. Sir, what is the justification that can be given to the fact that the overhead cost of performing non-parallel operations will be outvalued by performing operations in intra-operation parallelism? What are the possible conditions?

    ReplyDelete
    Replies
    1. Abhishek, we use parallelism for increasing the speed of execution of the query. Normally it would be required when we have to deal with huge data. Intra-operation parallelism is about processing a single operation (like sorting, joining, etc) in parallel. When we would try to execute these operations on huge amount of data in a single machine, we need to batch process the data. that is, for example, first 10000 records and second 10000 records, and so on. At the end, operation can be successfully performed but at the cost of time. When we perform the same in parallel, we do like batch processing but simultaneously at the same time.
      We would prefer parallelism when we need to work on huge amount of data, or we need to perform the query faster, or the data were already partitioned into different machines etc.

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