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    ACID Properties

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    berhe2121
    The document discusses the ACID properties of transactions in databases: Atomicity means that transactions contain multiple actions that either all occur or none occur. Consistency means transactions take the database from one consistent state to another. Isolation means concurrent transactions are not visible to each other until they are completed. Durability means committed transactions will not be lost even in event of abnormal termination.

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    ACID Properties

    Uploaded by

    berhe2121
    231 views3 pages
    The document discusses the ACID properties of transactions in databases: Atomicity means that transactions contain multiple actions that either all occur or none occur. Consistency means transactions take the database from one consistent state to another. Isolation means concurrent transactions are not visible to each other until they are completed. Durability means committed transactions will not be lost even in event of abnormal termination.

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    real time database

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    The document discusses the ACID properties of transactions in databases: Atomicity means that transactions contain multiple actions that either all occur or none occur. Consistency means transactions take the database from one consistent state to another. Isolation means concurrent transactions are not visible to each other until they are completed. Durability means committed transactions will not be lost even in event of abnormal termination.

    Copyright:

    © All Rights Reserved
    Download as DOCX, PDF, TXT or read online from Scribd
    Download as docx, pdf, or txt
    231 views3 pages

    ACID Properties

    Uploaded by

    berhe2121
    The document discusses the ACID properties of transactions in databases: Atomicity means that transactions contain multiple actions that either all occur or none occur. Consistency means transactions take the database from one consistent state to another. Isolation means concurrent transactions are not visible to each other until they are completed. Durability means committed transactions will not be lost even in event of abnormal termination.

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    2.

    1 ACID Properties of Transactions

    Most of what were calling transactional locking relates to the ability of a database
    management system (DBMS) to ensure reliable transactions that adhere to these
    ACID properties. ACID is an acronym that stands for Atomicity, Consistency,
    Isolation, and Durability. Each of these properties is described in more detail below.
    However, all of these properties are related and must be considered together. They
    are more like different views of the same object than independent things.

    2.1.1 Atomicity

    Atomicity means all or nothing. Transactions often contain multiple separate


    actions. For example, a transaction may insert data into one table, delete from
    another table, and update a third table. Atomicity ensures that either all of these
    actions occur or none at all.

    2.1.2 Consistency

    Consistency means that transactions always take the database from one consistent
    state to another. So, if a transaction violates the databases consistency rules, then
    the entire transaction will be rolled back.

    2.1.3 Isolation

    Isolation means that concurrent transactions, and the changes made within them,
    are not visible to each other until they complete. This avoids many problems,
    including those that could lead to violation of other properties. The implementation
    of isolation is quite different in different DBMS. This is also the property most often
    related to locking problems.

    2.1.4 Durability

    Durability means that committed transactions will not be lost, even in the event of
    abnormal termination. That is, once a user or program has been notified that a
    transaction was committed, they can be certain that the data will not be lost.

    Lock Contention

    Lock contention occurs when many database sessions all require frequent access to
    the same lock. This is also often called a "hot lock". The locks in question are only
    held for a short time by each accessing session, then released. This creates a
    "single lane bridge" situation. Problems are not noticeable when traffic is low (i.e.
    non-concurrent or low-concurrency situations). However, as traffic (i.e. concurrency)
    increases, a bottleneck is created.

    Overall, Lock Contention problems have a relatively low impact. They manifest
    themselves by impacting and limiting scalability. As concurrency increases, system
    throughput does not increase and may even degrade (as shown in Figure 1 below).
    Lock contention may also lead to high CPU usage on the database server.

    The best way to identify a lock contention problem is through analysis of statistical
    information on locks provided by the DBMS (see monitoring section below).

    Databases for Hard Real Time Systems

    MDARTS - is an example of a hard real time database system , it stands for


    multiprocessor database architecture for real time systems
    Used mainly in control applications, such as controlling machine tools and
    robots etc

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