RECOVERY MANAGER IN TERADATA

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RECOVERY MANAGER IN TERADATA

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In this article ,we will see RECOVERY MANAGER IN TERADATA

The Recovery Manager utility, rcvmanager, monitors and provides information about the progress of a Teradata Database system in recovery, including transaction rollbacks, because of a Teradata Database system crash or user abort.

The recovery process might include one or more of the following:

  • Online Transaction recovery
  • Down AMP recovery of changed data rows
  • Down AMP recovery of Teradata Database system level changes

Also, rcvmanager allows you to do the following:

  • Cancel the rollback of one or more specified host and session IDs
  • Set the priority level of rollbacks in progress for a specified host and session IDSet priority levels to optimize Teradata Database system recovery

Scenarios Runs From

Database Window or comparable interface to the Teradata Database console subsystem, such as cnsterm. Type start rcvmanager at the DBW command prompt.

Teradata Viewpoint Remote Console portlet

Host Utility Console

Prerequisites

You can run rcvmanager only while the Teradata Database is in one of the following states:

  • Logon
  • Logon/quiet
  • Logoff
  • Logoff/quiet
  • Startup (if the Teradata Database system has completed voting for transaction recovery)

Assigning Priority Levels

You can assign priority levels to Teradata Database system recovery or table rebuild by using the PRIORITY command feature of rcvmanager. Control over job priority is assigned by selecting one of three priority levels:

HIGH

MEDIUM

LOW

Teradata Database system recovery and disk rebuild are primarily I/O intensive tasks. The major portion of the time taken by a given task is involved in setting up for or waiting for completions of a disk or a BYNET message traffic operation. Very little manipulation or computation is required on the data once it is available.

If the competing work load of the Teradata Database system can be reasonably characterized, then you can gauge the impact of the priority changes to recovery and rebuild operations.

Changing Priority Levels for Rollback

rcvmanager also allows you to change the priority levels for rollback. To display or set the current Performance Group of the rollback for a particular session, use the ROLLBACK SESSION… PERFORMANCE GROUP command.

The priority associated with the specified Performance Group determines the priority of rollback for the specified host and session IDs.

Online Transaction Recovery

Online transaction recovery is automatically invoked by a Teradata Database system restart and includes the following processes:

  • Rolling back transactions that were not completed at the time of the crash or restart
  • Completing transactions that were committed

Changes made to underlying data by transactions are recorded in the Transient Journal (TJ). AMPs keep track of transactions in progress using the TJ which is stored on each AMP’s disk.

Transaction Recovery Sequence

The general sequence of a Teradata Database system recovery is as follows:

1 The status of each transaction on each online AMP is determined by the Teradata Database system.

All of the online AMPs at the time of the restart work together to determine which transactions were complete, and which ones were not completed. Completed transactions are ignored and incomplete ones are backed out. The process of rolling back incomplete transactions might take some time.

Write and exclusive locks are set against all data modified by incomplete transaction.

2 All locks needed for the recovery are set, and the Teradata Database system begins roll back or completion of the transactions.

3 The Teradata Database system accepts work and is operational.

Note: If new transactions reference the inconsistent data of to-be-rolled-back transactions, they are blocked until the recovery process restores the data and releases the lock.

4 Down AMP recovery begins.

Deferred Transaction Recovery

If the Teradata Database system crashes, a COLD restart is activated and an online transaction recovery or deferred recovery is started. The only time a deferred recovery is not done is when the operator enters a COLDWAIT restart.

Deferred transaction recovery allows new transactions to come in from the connected hosts. The process of bringing the Teradata Database system up after a crash causes the locks to be set. If new transactions should attempt to reference the inconsistent data of the to-be-rolled-back transactions, they are blocked until the recovery process restores the data and releases the lock.

 

Example:

<<<<  To list the tables which are under rollback

>list status;   <<<<<<  To see the recovery status

>RECOVERY PRIORITY;   <<<<<<<  To see the current recovery priority

>RECOVERY PRIORITY HIGH;   <<<<<<<   To change the recovery priority

Other useful syntaxes:

Thank you for giving your valuable time to read the above information.
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