If your Adaptive Server is used primarily between the hours of 8:00 a.m. and 5:00 p.m., Monday through Friday, you can run dbcc checks at night and on weekends so that the checks do not have a significant impact on your users. If your tables are not extremely large, you can run a complete set of dbcc commands fairly frequently.
dbcc checkstorage and dbcc checkcatalog provide the best coverage at the lowest cost, assure recovery from backups. You can run dbcc checkdb or dbcc checktable less frequently to check index sort order and consistency. This check does not need to be coordinated with any other database maintenance activity. Reserve object-level dbcc checks and those checks that use the fix option for further diagnosis and correction of faults found by dbcc checkstorage.
If your Adaptive Server is used 24 hours a day, 7 days a week, you may want to limit the resource usage of dbcc checkstorage by limiting the number of worker processes or by using application queues. If you decide not to use dbcc checkstorage, you may want to schedule a cycle of checks on individual tables and indexes using dbcc checktable, dbcc tablealloc, and dbcc indexalloc. At the end of the cycle, when all tables have been checked, you can run dbcc checkcatalog and back up the database. For information on using application queues, see Chapter 5, “Distributing Engine Resources,” in Performance and Tuning: Basics.
Some sites with 24-hour, high-performance demands run dbcc checks by:
Dumping the database to tape
Loading the database dump into a separate Adaptive Server to create a duplicate database
Running dbcc commands on the duplicate database
Running dbcc commands with the fix options on appropriate objects in the original database, if errors are detected that can be repaired with the fix options
The dump is a logical copy of the database pages; therefore, problems found in the original database are present in the duplicate database. This strategy is useful if you are using dumps to provide a duplicate database for reporting or some other purpose.
Schedule the use of dbcc commands that lock objects to avoid interference with business activities. For example, dbcc checkdb acquires locks on all objects in the database while it performs the check. You cannot control the order in which it checks the objects. If you are running an application that uses table4, table5, and table6, and running dbcc checkdb takes 20 minutes to complete, the application will be blocked from accessing these tables, even when the command is not checking them.
