generate barcode in vb.net Lesson 3: Designing Failover and Failback Strategies in Visual C#

Generation UPC-A in Visual C# Lesson 3: Designing Failover and Failback Strategies

Lesson 3: Designing Failover and Failback Strategies
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1. Restore any transaction logs to bring the secondary as far forward in time as possible. 2. Restore the last transaction log using the WITH RECOVERY option. 3. Execute sp_change_users_login for each SQL Server login on the secondary. 4. If necessary, start any endpoints. 5. Verify security permissions. 6. Change the connection strings for applications to point at the secondary. 7. Start any jobs that are needed, such as the job to start backing up the database. The first task during a failover is to ensure minimum loss of data. If there are any transaction logs that have not yet been applied to the secondary, they should be restored. The last transaction log to be restored should specify the WITH RECOVERY option. If all transaction logs have already been applied, you need to issue a RESTORE DATABASE WITH RECOVERY command. This command brings the database online, after which additional transaction log restores are no longer possible. After you bring the secondary database online, you should verify all other objects that a re n e e d e d fo r t h e a p p l i c a t i o n t o f u n c t i o n . Yo u s h o u l d e xe c u t e t h e sp_change_users_login procedure for every SQL Server login to ensure a correct map ping to a user in the secondary database. You should also verify any endpoints, linked servers, or other objects that the application needs. After verifying that all objects exist, the security permissions are correct, and the database is accessible, you need to connect the application to the database to restore operations to end users. You should perform any remaining administrative tasks only after you have restored normal operations. Remove any pieces of the log shipping configuration, generally the copy and restore jobs. You should also create a job that executes backups against the database. The database that was the secondary has now become the primary database that accepts transactions, so it needs to be as protected as much as possible. If you have copied all the necessary instance-level objects to the secondary as well as verifying each object as much as possible, the time to execute the failover of applications from the primary to the secondary can be a matter of one or two minutes. After the original primary is repaired and brought back online, you reenable log ship ping with the original primary being demoted to a secondary. This reestablishes redun dancy through log shipping without incurring an additional outage to the application.
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After you have failed over to the secondary, the database begins to diverge from the original source. By enabling transactions to be issued, the secondary database has been promoted to the primary and is now the database of record for the application. When the failed server is repaired and brought back online, it should assume the role of standby. A failback to the original primary should occur for only two reasons:
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Management dictates that applications run against a particular server. Performance or fault tolerance degrades when the application is connected to the secondary.
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Having management dictate that applications should be running against a particular SQL Server instance is never a good idea. This type of decision should be left up to the technical team. As long as the applications are running and the business is functional, management shouldn t care about the technical implementation. Sometimes it is not possible to allocate a standby that has the same capacity as the pri mary. When the standby has fewer resources, application performance can degrade. In this case, you should get applications switched back to the failed primary as soon as possible. Because transactions would have been issued against the database on the standby, you need to get a current copy of the database back to the original primary, which you can do with a minimum of downtime to the applications by performing the following steps: 1. Reinitialize the primary with a backup from the standby, making sure to specify the NO RECOVERY option. 2. Apply the most recent differential and any additional transaction log backups to the primary, specifying the NO RECOVERY option for all restores. 3. Copy any instance-level objects that you have created or changed on the standby back to the primary. 4. Continue repeating step 2 until you are prepared to switch applications back to the primary. 5. Stop the transaction log backup job on the primary. 6. Disconnect all applications from the standby and prevent access by disabling the logins, using the following command:
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