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Teradata RDBMS Database Administration - NCR

NCR Teradata RDBMS Database Administration - NCR , 2004. - 616 p.
Download (direct link): teradatadatabaseadmin2004.pdf
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9 - 10

Teradata RDBMS Database Administration Chapter 9: Stopping and Restarting the System

Startup and Recovery

Sequence Teradata RDBMS .
8 reads the syscheckrc file to register threshold levels used by syscheck. (For details, see "Resource Check Tools Utility" in Teradata RDBMS Utilities.)
9 recalculates space consumption and updates the system tables.
10 performs transaction recovery (see "Transaction Recovery" on page 9-9).
11 if CR is enabled, instructs each AMP to map a view of its FSG cache into its virtual address space (see "Managing I/O with Cylinder Read" on page 15-2).
12 reconnects all sessions. For network sessions, the Teradata Gateway: Retrieves (from the PCLXSESSINFO parcel) the seed and hash of the password associated with each disconnected session Rehashes each password using the seed Compares the new hash value to the saved hash value Reconnects each session with a password hash match.

Transaction Recovery

Teradata RDBMS automatically recovers all transactions that were running at the time of the restart.

Transaction recovery involves determining whether transactions being processed by an online AMP when the database restarted should be committed or rolled back.

When an AMP completes work on a particular transaction, it places an End Transaction marker for that transaction in the Transient Journal (TJ).

During transaction recovery, the AMPs examine their TJ for an End Transaction marker for every transaction in progress when the restart occurred. For a transaction to qualify as committed, the End Transaction marker must be found by every AMP involved. Otherwise, the transaction is rolled back.

The Teradata RDBMS automatically does the following for recovery:

Completes committed transactions and releases spool files

Recovers data from system recovery journals

Rolls back uncommitted transactions

Note: Rolled back transactions do not conform to the absolute policy of the Priority Scheduler (see "Priority Scheduler" in Teradata RDBMS Utilities).

Warning: For rows using identity column, if a roll back occurs, the assigned numbers may be lost and will not be re-generated for the same rows when the request is re-submitted.

9 - 10 Teradata RDBMS Database Administration

Chapter 9: Stopping and Restarting the System

Startup and Recovery

When possible, reconnects sessions that were active at the time of restart

For more information, see Chapter 8: "Archiving, Restoring and Recovering Data."

If a disk failed, replace the physical disk. See "Moving Vprocs and Data Rows for Hardware Upgrades" on page A-15 for more information.

Using System Recovery Journals

The system recovery journals used to complete transaction recovery include:

Journal Function Location
Transient Journal (TJ) Determines whether in-progress transactions are committed Completes committed transactions Rolls back uncommitted transactions. Local to each AMP
Down AMP Recovery Journal, including: Changed Row Journal (CJ) Ordered System Change Journal (OSCJ) Contain information on updates to fallback tables that occurred while an AMP was down (offline). Used to update the fallback tables on the down AMP prior to bringing that vproc back online. Note: Non-fallback data on the down vproc cannot be updated while the vproc is down. Remaining active AMPs in the cluster

Performing Online and Offline Catch-up

When Teradata RDBMS undergoes a cold restart, the system must decide whether to perform the recovery process when an AMP is offline.

An AMP can usually catch up after being brought back online if the following are true:

The Change Row Journal (CJ) count is less than 3000

The Ordered System Change Journal (OSCJ) count is 0

The Transient Journal (TJ) count is 0

No HUT locks are present in the cluster

Otherwise, the AMP is kept current even though remaining offline. Every five minutes, a background task is activated that applies changes from the CJ and OSCJ to keep the offline AMP caught up until the situation is resolved.

Restarting the DB Window (UNIX Only)

When startup is complete, on an MPP system you can restart the DB Window as follows:

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Teradata RDBMS Database Administration Chapter 9: Stopping and Restarting the System

Startup and Recovery

Step Action
1 Be sure xserver is running.
2 On the control node (the lowest numbered node that is up), enter: export DISPLAY = <IP address of PC> #/usr/ntos/bin/xdbw The outline for the DBW should appear on the screen.
3 The DB Window does not reconnect until restart is complete. If an error window appears with the message: Attempting to connect to CNS . . . and remains in the middle of the DBW, it may be that Teradata RDBMS restart is still in progress. Wait a few moments before trying again. (See Teradata RDBMS Database Window for more information.)

Startup Event and Status Logs

Startup events and status are logged as follows:
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