HP NonStop RDF, Руководство по управлению

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you need to restart updating. When restarted, the only updaters that do any work are those that
terminated prematurely last time. When they reach the special record, they stop and the purger
then logs the event 908. See the section
“RDF and NonStop SQL DDL Operations” (page 151) for
further discussion.
Without Shared Access
For all operations that do not include With Shared Access, you must stop your applications on
your primary system first because these operations are only allowed when all tables are closed.
To coordinate such DDL operations in an RDF environment, you must stop your applications
and then stop RDF when you are certain the updaters have applied all audit up to the point
when you stopped your applications. There are two safe ways to do this: stop TMF momentarily
after stopping your applications, or execute the STOP RDF, DRAIN command when you are
certain your applications have all stopped. With the Stop TMF method, RDF will shut down
when it has reached the stop-TMF audit record, thereby guaranteeing that all audit has been
applied to the backup database up to the stop point. With the DRAIN method, RDF shuts down
when the updaters have processed all audit up to the point where you issued the STOP RDF,
DRAIN command, which must be issued after you stopped your applications. If no updaters
stopped prematurely, the purger logs RDF event 852, and it now safe for you to perform the
same DDL change on the primary and backup systems before restarting RDF and your
applications.
Adding a New Column
This is an operation that cannot be performed With Shared Access. To minimize application
downtime, you can coordinate the operation as follows. Stop the RDF updaters with a simple
STOP UPDATE command. When the updaters have stopped, add the column to your backup
database and then restart update. Note, at this point, the new column is in the backup database
but not yet on the primary. When the updaters update subsequent rows with the new column,
the disk process adds the default value to the new column. Next, you perform a switchover
operation (detailed in
Chapter 5 ), start RDF on your backup system with update off, and then
start your applications on your backup system. Add the column to the database on your former
primary system (it is now the backup of your new RDF environment), and then START UPDATE.
When RDF has caught up and at your convenience, perform a new switchover operation to move
your application processing back to your primary system.
Making Changes to Database Structures 161