DBCC Commands for SQL Server

DBCC Commands:

DBCC commands are most useful for performance and troubleshooting.
The DBCC Commands are used in Maintenance, Informational use, Validation on a database, index, or file group. Theses commands are helpful to check physical and logical consistency of database. Some DBCC statements fix errors automatically. Here I am showing some commands that are frequently used.

Command	Description	Level	When to Check
DBCC SQLPERF(logspace)	--To see transaction log size of each database on Server.	Server Level	Weekly
DBCC SHOWFILESTATS	--Show Total Extents and used extents for database	Database Level	Weekly
DBCC CHECKCATALOG	--Checks for catalog/tables consistency within the specified database	Database Level	Weekly
DBCC CHECKCONSTRAINTS	--Checks the integrity of a specified constraint or all constraints on a specified table in the current database	Database Level	When you suspect that there are rows in your tables that do not meet the constraints/rules.
DBCC CHECKALLOC	-- checks page usage and allocation in the database.	Database Level	if allocation errors are found for the database
DBCC CHECKTABLE(tablename)	--It verifies index and data page links, index sort order, page pointers, index pointers, data page integrity, and page offsets on table.	Table level	Whenever required.
DBCC CHECKIDENT(tablename)	--Checking identity information,return current identity value of specified table	Table Level	Whenever required.
DBCC DBREINDEX(tablename)	-- rebuilds an index for a table or all indexes defined for a table.	Table level	(should not used rather use ALTER INDEX command)
DBCC INDEXDEFRAG (databasename, tablename,indexname)	--defragment clustered and nonclustered indexes on tables and views	Table/View Level	(Should not use, Replacement is ALTER INDEX ... REORGANISE)
SELECT request_id FROM sys.dm_exec_requests WHERE session_id = @@spid;	--returns request_id
DBCC INPUTBUFFER(sessionid)	--to view the last statement sent by the client connection to SQL Server	Database level	Whenever required
DBCC SHRINKDATABASE(databasename)	--Shrinks the size of the data and log files in the specified database	Database Level	Avoid executing this command during busy periods in production
DBCC SHRINKFILE(file_id) Use exec sp_helpfile  to know filename,fileid,filegroup,size	--allows you to shrink the size of individual data and log files	Database level	Avoid, as in most cases the database will just regrow and shrinking data files causes fragmentation.
DBCC TRACEOFF	--used to disable tracing	Server Level
DBCC TRACEON	--used to enable tracing	Server Level
DBCC TRACESTATUS	--used to know trace status with TraceFlag,Status,Global,Session	Server Level
DBCC USEROPTIONS	--Returns the SET options active (set) for the current connection	Server Level	Whenever required