DBCC (Database consistency checker) are used to check the consistency of the databases. The DBCC commands are most useful for performance and trouble shooting exercises.
I have listed down and explained all the DBCC commands available in SQL Server 2005, with examples.
The DBCC Commands broadly falls into four categories:
- Maintenance
- Informational
- Validation
- Miscellaneous
Maintenance Commands
Performs maintenance tasks on a database, index, or filegroup.
1. CLEANTABLE – Reclaims space from the dropped variable-length columns in tables or index views.
DBCC CLEANTABLE (‘AdventureWorks’,’Person.Contact’,0)
2. DBREINDEX – Builds one or more indexes for the table in the specified database. (Will be removed in the future version, use ALTER INDEX instead)
USE AdventureWorks
DBCC DBREINDEX (‘Person.Contact’,’PK_Contact_ContactID’,80)
3. DROPCLEANBUFFERS – Removes all clean buffers from buffer pool.
DBCC DROPCLEANBUFFERS
4. FREEPROCCACHE – Removes all elements from the procedure cache
DBCC FREEPROCCACHE
5. INDEXDEFRAG – Defragments indexes of the specified table or view.
DBCC INDEXDEFRAG (‘AdventureWorks’, ‘Person.Address’, PK_Address_AddressID)
6. SHRINKDATABASE – Shrinks the size of the data and log files in the specified database
DBCC SHRINKDATABASE (‘AdventureWorks‘, 10)
7. SHRINKFILE – Shrinks the size of the specified data or log file for the current database or empties a file by moving the data from the specified file to other files in the same filegroup, allowing the file to be removed from the database.
USE AdventureWorks;
— Shrink the truncated log file to 1 MB.
DBCC SHRINKFILE (AdventureWorks_Log, 1)
8. UPDATEUSAGE – Reports and corrects pages and row count inaccuracies in the catalog views.
DBCC UPDATEUSAGE (AdventureWorks)
Informational Commands
Performs tasks that gather and display various types of information.
1. CONCURRENCYVIOLATION – is maintained for backward compatibility. It runs but returns no data.
DBCC CONCURRENCYVIOLATION
2. INPUTBUFFER – Displays the last statement sent from a client to an instance of Microsoft SQL Server 2005.
DBCC INPUTBUFFER (52)
3. OPENTRAN – Displays information about the oldest active transaction and the oldest distributed and nondistributed replicated transactions, if any, within the specified database.
DBCC OPENTRAN;
4. OUTPUTBUFFER – Returns the current output buffer in hexadecimal and ASCII format for the specified session_id.
DBCC OUTPUTBUFFER (52)
5. PROCCACHE – Displays information in a table format about the procedure cache.
DBCC PROCCACHE
6. SHOW_STATISTICS – Displays the current distribution statistics for the specified target on the specified table
USE AdventureWorks
DBCC SHOW_STATISTICS (‘Person.Address’, AK_Address_rowguid)
7. SHOWCONTIG – Displays fragmentation information for the data and indexes of the specified table or view.
USE AdventureWorks
DBCC SHOWCONTIG (‘HumanResources.Employee’);
8. SQLPERF – Provides transaction log space usage statistics for all databases. It can also be used to reset wait and latch statistics.
DBCC SQLPERF(LOGSPACE)
9. TRACESTATUS – Displays the status of trace flags.
DBCC TRACESTATUS(-1)
10. USEROPTIONS – Returns the SET options active (set) for the current connection.
DBCC USEROPTIONS
Validation Commands
Performs validation operations on a database, table, index, catalog, filegroup, or allocation of database pages.
1. CHECKALLOC – Checks the consistency of disk space allocation structures for a specified database.
DBCC CHECKALLOC (AdventureWorks)
2. CHECKCATALOG – Checks for catalog consistency within the specified database.
DBCC CHECKCATALOG (AdventureWorks)
3. CHECKCONSTRAINTS – Checks the integrity of a specified constraint or all constraints on a specified table in the current database.
DBCC CHECKCONSTRAINTS WITH ALL_CONSTRAINTS
4. CHECKDB – Checks the logical and physical integrity of all the objects in the specified database.
DBCC CHECKDB (AdventureWorks)
5. CHECKFILEGROUP – Checks the allocation and structural integrity of all tables and indexed views in the specified filegroup of the current database.
USE AdventureWorks
DBCC CHECKFILEGROUP
6. CHECKIDENT – Checks the current identity value for the specified table and, if it is needed, changes the identity value.
USE AdventureWorks;
DBCC CHECKIDENT (‘HumanResources.Employee’)
7. CHECKTABLE – Checks the integrity of all the pages and structures that make up the table or indexed view.
USE AdventureWorks;
DBCC CHECKTABLE (‘HumanResources.Employee’)
Miscellaneous Commands
Performs miscellaneous tasks such as enabling trace flags or removing a DLL from memory.
1. dllname (FREE) – Unloads the specified extended stored procedure DLL from memory.
DBCC xp_sample (FREE)
2. TRACEOFF – Disables the specified trace flags.
DBCC TRACEOFF (3205)
3. HELP – Returns syntax information for the specified DBCC command.
— List all the DBCC commands
DBCC HELP (‘?’)
— Show the Syntax for a given DBCC commnad
DBCC HELP (‘checkcatalog’)
4. TRACEON – Enables the specified trace flags.
DBCC TRACEON (3205)
Good Luck!
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