close
This essay has been submitted by a student. This is not an example of the work written by professional essay writers.

Database Recovery Techniques Used in Distributed Environment

downloadDownload printPrint

Pssst… we can write an original essay just for you.

Any subject. Any type of essay.

We’ll even meet a 3-hour deadline.

Get your price

121 writers online

blank-ico
Download PDF

Data loss is any process or event that causes data deletion, corruption, or unreadable by a user and or software or application. It occurs when data cannot be utilized by the data owner or requesting application, applying to any data both at rest and in motion .It is also known as data leakage.

Possible causes of data loss could be; hardware failure, human error, software corruption, computer viruses, theft, hardware destruction.

Levels of Possible Recovery

  1. Recovery to its correct state- returning the database to its original state before any data loss or corruption occurred. This is usually the best outcome when trying to recover any lost data.
  2. Recovery to a checkpoint -returning a database to a previously saved point .This recovery typically doesn’t preserve any recently entered data.
  3. Recovery to previous state – Restore the database to a specific point in time.
  4. Recovery to valid state – The database contains some of the information from the correct state. There is no false data, although pieces may be missing.
  5. Recovery to a consistent state- brings all data files in the database to a consistent state; all files are restored as of a single point-in-time. In order to recuperate from database failure, database management systems resort to a number of recovery management techniques.

The typical strategies for database recovery are:

  1. In case of soft failures that result in inconsistency of database, recovery strategy includes transaction undo or rollback. However, sometimes, transaction redo may also be adopted to recover to a consistent state of the transaction.
  2. In case of hard failures resulting in extensive damage to database, recovery strategies encompass restoring a past copy of the database from archival backup. A more current state of the database is obtained through redoing operations of committed transactions from transaction log.

COMMON DATABASE RECOVERY TECHNIQUES

  1. Recovery from Power Failure
  2. Power failure causes loss of information in the non-persistent memory. When power is restored, the operating system and the database management system restart. Recovery manager initiates recovery from the transaction logs.

    In case of immediate update mode, the recovery manager takes the following actions -Transactions which are in active list and failed list are undone and written on the abort list.

    Transactions which are in before-commit list are redone.

    No action is taken for transactions in commit or abort lists.

    In case of deferred update mode, the recovery manager takes the following actions -Transactions which are in the active list and failed list are written onto the abort list. No undo operations are required since the changes have not been written to the disk yet.

    Transactions which are in before-commit list are redone.

    No action is taken for transactions in commit or abort lists.

  3. Recovery from Disk Failure
  4. A disk failure or hard crash causes a total database loss. To recover from this hard crash, a new disk is prepared, then the operating system is restored, and finally the database is recovered using the database backup and transaction log. The recovery method is same for both immediate and deferred update modes.

    The recovery manager takes the following actions -The transactions in the commit list and before-commit list are redone and written onto the commit list in the transaction log.

    The transactions in the active list and failed list are undone and written onto the abort list in the transaction log.

  5. Checkpointing
  6. Checkpoint is a point of time at which a record is written onto the database from the buffers. As a consequence, in case of a system crash, the recovery manager does not have to redo the transactions that have been committed before checkpoint. Periodical checkpointing shortens the recovery process.

    There are two types of checkpointing; fuzzy and consistent checkpointing.

    Consistent checkpointing creates a consistent image of the database at checkpoint. During recovery, only those transactions which are on the right side of the last checkpoint are undone or redone. The transactions to the left side of the last consistent checkpoint are already committed and needn’t be processed again.

    In fuzzy checkpointing, at the time of checkpoint, all the active transactions are written in the log. In case of power failure, the recovery manager processes only those transactions that were active during checkpoint and later. The transactions that have been committed before checkpoint are written to the disk and hence need not be redone.

  7. Transaction Recovery Using UNDO / REDO
  8. Transaction recovery is done to eliminate the adverse effects of faulty transactions rather than to recover from a failure. Faulty transactions include all transactions that have changed the database into undesired state and the transactions that have used values written by the faulty transactions.

    Transaction recovery in these cases is a two-step process -UNDO all faulty transactions and transactions that may be affected by the faulty transactions.

    REDO all transactions that are not faulty but have been undone due to the faulty transactions.

Steps for the UNDO operation are:

  • If the faulty transaction has done INSERT, the recovery manager deletes the data item(s) inserted.
  • If the faulty transaction has done DELETE, the recovery manager inserts the deleted data item(s) from the log.
  • If the faulty transaction has done UPDATE, the recovery manager eliminates the value by writing the before-update value from the log.

Steps for the REDO operation are:

  • If the transaction has done INSERT, the recovery manager generates an insert from the log.
  • If the transaction has done DELETE, the recovery manager generates a delete from the log.
  • If the transaction has done UPDATE, the recovery manager generates an update from the log.

Tools /softwares used for database recovery

  • SQL database recovery –this software retrieves database by tables.

This tool offers high accuracy recovery of file objects like: tables, views, stored procedure and programmability. It also enables users to see preview of recovered data before saving.

  • Apex SQL recover-this tool enables one to recover from live (real-time) databases transaction logs and detached DB.
  • Recover oracle Databases-it recovers and repairs inaccessible or corrupt oracle DB created in different oracle versions like oracle 9i.
  • Stellar phoenix SQL database Repair- restores tables, indexes, reports, rules, stored procedures .Apart from that it facilitates selective recovery of specific tables from a huge DB.

infoRemember: This is just a sample from a fellow student.

Your time is important. Let us write you an essay from scratch

100% plagiarism-free

Sources and citations are provided

Find Free Essays

We provide you with original essay samples, perfect formatting and styling

Cite this Essay

To export a reference to this article please select a referencing style below:

Database Recovery Techniques Used in Distributed Environment. (2018, December 03). GradesFixer. Retrieved July 29, 2021, from https://gradesfixer.com/free-essay-examples/database-recovery-techniques-used-in-distributed-environment/
“Database Recovery Techniques Used in Distributed Environment.” GradesFixer, 03 Dec. 2018, gradesfixer.com/free-essay-examples/database-recovery-techniques-used-in-distributed-environment/
Database Recovery Techniques Used in Distributed Environment. [online]. Available at: <https://gradesfixer.com/free-essay-examples/database-recovery-techniques-used-in-distributed-environment/> [Accessed 29 Jul. 2021].
Database Recovery Techniques Used in Distributed Environment [Internet]. GradesFixer. 2018 Dec 03 [cited 2021 Jul 29]. Available from: https://gradesfixer.com/free-essay-examples/database-recovery-techniques-used-in-distributed-environment/
copy to clipboard
close

Sorry, copying is not allowed on our website. If you’d like this or any other sample, we’ll happily email it to you.

    By clicking “Send”, you agree to our Terms of service and Privacy statement. We will occasionally send you account related emails.

    close

    Attention! This essay is not unique. You can get a 100% Plagiarism-FREE one in 30 sec

    Receive a 100% plagiarism-free essay on your email just for $4.99
    get unique paper
    *Public papers are open and may contain not unique content
    download public sample
    close

    Sorry, we could not paraphrase this essay. Our professional writers can rewrite it and get you a unique paper.

    close

    Thanks!

    Your essay sample has been sent.

    Want us to write one just for you? We can custom edit this essay into an original, 100% plagiarism free essay.

    thanks-icon Order now
    boy

    Hi there!

    Are you interested in getting a customized paper?

    Check it out!
    Having trouble finding the perfect essay? We’ve got you covered. Hire a writer
    exit-popup-close

    Haven't found the right essay?

    Get an expert to write you the one you need!

    exit-popup-print

    Professional writers and researchers

    exit-popup-quotes

    Sources and citation are provided

    exit-popup-clock

    3 hour delivery

    exit-popup-persone