Concurrent Executions

Multiple transactions are allowed to run concurrently in the system. The advantages of concurrent executions are as follows: Increased processor and disk utilization: The increased processor and allowance of the disk utilization leads to better transaction throughput. One transaction can be using the CPU while another is reading from or writing to the disk. Reduced average response time for transactions: Short transactions do not need to wait behind the long ones. Concurrency control schema: The mechanism to achieve isolation is known as concurrency control scheme that is to control the interaction among the concurrent transactions in order to prevent them from destroying the consistency of the database. Schedules: The sequence of instruction that specify the chronological order in which instructions of concurrent transactions are executed is called schedule. For a particular set of transactions a schedule must consist of all instructions of those transactions. It must preserve the order in which the instructions appear in each individual transaction. A transaction that successfully completes its execution will have the commit instructions as the last statement. A transaction that fails to complete its execution successfully will have abort instructions as the last statement.

Summary

Multiple transactions are allowed to run concurrently in the system. The advantages of concurrent executions are as follows: Increased processor and disk utilization: The increased processor and allowance of the disk utilization leads to better transaction throughput. One transaction can be using the CPU while another is reading from or writing to the disk. Reduced average response time for transactions: Short transactions do not need to wait behind the long ones. Concurrency control schema: The mechanism to achieve isolation is known as concurrency control scheme that is to control the interaction among the concurrent transactions in order to prevent them from destroying the consistency of the database. Schedules: The sequence of instruction that specify the chronological order in which instructions of concurrent transactions are executed is called schedule. For a particular set of transactions a schedule must consist of all instructions of those transactions. It must preserve the order in which the instructions appear in each individual transaction. A transaction that successfully completes its execution will have the commit instructions as the last statement. A transaction that fails to complete its execution successfully will have abort instructions as the last statement.

Things to Remember

  • Multiple transactions are allowed to run concurrently in the system. The advantages of concurrent executions are as follows:
    Increased processor and disk utilization: The increased processor and allowance of the disk utilization leads to better transaction throughput. One transaction can be using the CPU while another is reading from or writing to the disk.
    Reduced average response time for transactions: Short transactions do not need to wait behind the long ones.

  • The mechanism to achieve isolation is known as concurrency control scheme that is to control the interaction among the concurrent transactions in order to prevent them from destroying the consistency of the database.
  • The sequence of instruction that specify the chronological order in which instructions of concurrent transactions are executed is called schedule. For a particular set of transactions a schedule must consist of all instructions of those transactions.
  • A transaction that successfully completes its execution will have the commit instructions as the last statement. A transaction that fails to complete its execution successfully will have abort instructions as the last statement.

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Concurrent Executions

Concurrent Executions

Concurrent Executions

Multiple transactions are allowed to run concurrently in the system. The advantages of concurrent executions are as follows:

  • Increased processor and disk utilization: The increased processor and allowance of the disk utilization leads to better transaction throughput. One transaction can be using the CPU while another is reading from or writing to the disk.
  • Reduced average response time for transactions: Short transactions do not need to wait for the long ones.

Concurrency control schema: The mechanism to achieve isolation is known as concurrency control scheme that is to control the interaction among the concurrent transactions in order to prevent them from destroying the consistency of the database.

Schedules: The sequence of instruction that specify the chronological order in which instructions of concurrent transactions are executed is called schedule. For a particular set of transactions a schedule must consist of all instructions of those transactions. It must preserve the order in which the instructions appear in each individual transaction.

A transaction that successfully completes its execution will have the commit instructions as the last statement. A transaction that fails to complete its execution successfully will have abort instructions as the last statement.

A serial schedule in which T1 is followed by T2: Schedule 1

.

A serial schedule where T2 is followed by T1: Schedule 2

.

Let T1 and T2 be the transactions defined previously. The following schedule is not a serial schedule but it is equivalent to Schedule 1. In Schedule 1, 2 and 3 the sum A + B is preserved.

The following concurrent schedule does not preserve the value of (A + B).

References:

  1. H.F.Korth and A. Silberschatz,"Database system concepts",McGraw Hill,2010
  2. A.K.Majumdar and p, Bhatt acharya,"Database Management Systems",Tata McGraw Hill,India,2004
  3. F.Korth, Henry. Database System Concepts. 6th edition.

Lesson

Transactions processing and Concurrency Control

Subject

Computer Engineering

Grade

Engineering

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