Monday, July 18, 2011

SQL Server interview questions: - Describe DBCC?

DBCC (Database Consistency Checker Commands) is used to check logical and
physical consistency of database structure.DBCC statements can fix and detect
problems. These statements are grouped in to four categories:-

• Maintenance commands like DBCC DBREINDEX, DBCC DBREPAR etc, they are mainly
used for maintenance tasks in SQL SERVER.

• Miscellaneous commands like DBCC ROWLOCK, DBCC TRACEO etc, they are mainly
used for enabling row-level locking or removing DLL from memory.

• Status Commands like DBCC OPENTRAN, DBCC SHOWCONTIG etc , they are mainly used
for checking status of the database.

• Validation Commands like DBCC CHECKALLOC, DBCCCHECKCATALOG etc , they perform
validation operations on database.

Note :- Check MSDN for list of all DBCC commands, it is very much possible specially during
DBA interviews they can ask in depth individual commands.

Below is a sample screen in which DBCC SHOWCONTIG command is run. DBCC
SHOWCONTIG is used to display fragmentation information for the data and indexes
of the specified table.In the sample screen “Customer” table is checked for

DBCC SHOWCONTIG command in action.

Fragmentation information. If “Scan density” is 100 then everything is contigious.The above image has scan density of 95.36% which is decent percentage. So such type of useful information can be collected by DBCC command and database performance and maintenance can be improved.

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