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DBCC CHECKFILEGROUP (Transact-SQL)

  • Straipsnis

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance

Checks the allocation and structural integrity of all tables and indexed views in the specified filegroup of the current database.

Transact-SQL syntax conventions

Syntax

DBCC CHECKFILEGROUP
[
    [ ( { filegroup_name | filegroup_id | 0 }
        [ , NOINDEX ]
  ) ]
    [ WITH
        {
            [ ALL_ERRORMSGS | NO_INFOMSGS ]
            [ , TABLOCK ]
            [ , ESTIMATEONLY ]
            [ , PHYSICAL_ONLY ]
            [ , MAXDOP  = number_of_processors ]
        }
    ]
]

Arguments

filegroup_name

The name of the filegroup in the current database for which to check table allocation and structural integrity. If not specified, or if 0 is specified, the default is the primary filegroup. Filegroup names must comply with the rules for identifiers.
filegroup_name can't be a FILESTREAM filegroup.

filegroup_id

The filegroup identification (ID) number in the current database for which to check table allocation and structural integrity.

NOINDEX

Specifies that intensive checks of nonclustered indexes for user tables shouldn't be performed. This decreases the overall execution time. NOINDEX doesn't affect system tables because DBCC CHECKFILEGROUP always checks all system table indexes.

ALL_ERRORMSGS

Displays an unlimited number of errors per object. All error messages are displayed by default. Specifying or omitting this option has no effect.

NO_INFOMSGS

Suppresses all informational messages.

TABLOCK

Causes DBCC CHECKFILEGROUP to obtain locks instead of using an internal database snapshot.

ESTIMATE ONLY

Displays the estimated amount of tempdb space required to run DBCC CHECKFILEGROUP with all the other specified options.

PHYSICAL_ONLY

Limits the checking to the integrity of the physical structure of the page, record headers and the physical structure of B-trees. Designed to provide a small overhead check of the physical consistency of the filegroup, this check can also detect torn pages, and common hardware failures that can compromise data. A full run of DBCC CHECKFILEGROUP may take considerably longer than in earlier versions. This behavior occurs because of the following reasons:

  • The logical checks are more comprehensive.
  • Some of the underlying structures to be checked are more complex.
  • Many new checks have been introduced to include the new features.

Note

Documentation uses the term B-tree generally in reference to indexes. In rowstore indexes, the Database Engine implements a B+ tree. This does not apply to columnstore indexes or indexes on memory-optimized tables. For more information, see the SQL Server and Azure SQL index architecture and design guide.

Therefore, using the PHYSICAL_ONLY option may cause a much shorter run-time for DBCC CHECKFILEGROUP on large filegroups and is therefore recommended for frequent use on production systems. We still recommend that a full run of DBCC CHECKFILEGROUP is performed periodically. The frequency of these runs depends on factors specific to individual businesses and production environments. PHYSICAL_ONLY always implies NO_INFOMSGS and isn't allowed with any one of the repair options.

Note

Specifying PHYSICAL_ONLY causes DBCC CHECKFILEGROUP to skip all checks of FILESTREAM data.

MAXDOP

Applies to: SQL Server 2014 Service Pack 2 and later versions

Overrides the max degree of parallelism configuration option of sp_configure for the statement. The MAXDOP can exceed the value configured with sp_configure. If MAXDOP exceeds the value configured with Resource Governor, the Database Engine uses the Resource Governor MAXDOP value, described in ALTER WORKLOAD GROUP (Transact-SQL). All semantic rules used with the max degree of parallelism configuration option are applicable when you use the MAXDOP query hint. For more information, see Configure the max degree of parallelism Server Configuration Option.

Caution

If MAXDOP is set to zero then the server chooses the max degree of parallelism.

Remarks

DBCC CHECKFILEGROUP and DBCC CHECKDB are similar DBCC commands. The main difference is that DBCC CHECKFILEGROUP is limited to the single specified filegroup and required tables.

DBCC CHECKFILEGROUP performs the following commands:

Running DBCC CHECKALLOC or DBCC CHECKTABLE separately from DBCC CHECKFILEGROUP isn't required.

Internal database snapshot

DBCC CHECKFILEGROUP uses an internal database snapshot to provide the transactional consistency that it must have to perform these checks. For more information, see View the Size of the Sparse File of a Database Snapshot (Transact-SQL) and the DBCC internal database snapshot usage section in DBCC (Transact-SQL).

If a snapshot can't be created, or the TABLOCK option is specified, DBCC CHECKFILEGROUP acquires locks to obtain the required consistency. In this case, an exclusive database lock is required to perform the allocation checks, and shared table locks are required to perform the table checks. TABLOCK causes DBCC CHECKFILEGROUP to run faster on a database under heavy load, but decreases the concurrency available on the database while DBCC CHECKFILEGROUP is running.

Note

Running DBCC CHECKFILEGROUP against tempdb does not perform any allocation checks and must acquire shared table locks to perform table checks. This is because, for performance reasons, database snapshots are not available on tempdb. This means that the required transactional consistency cannot be obtained.

Check objects in parallel

By default, DBCC CHECKFILEGROUP performs parallel checking of objects. The degree of parallelism is automatically determined by the query processor. The maximum degree of parallelism is configured just like parallel queries. To restrict the maximum number of processors available for DBCC checking, use sp_configure. For more information, see Configure the max degree of parallelism Server Configuration Option.

Parallel checking can be disabled by using Trace Flag 2528. For more information, see Trace Flags (Transact-SQL).

Nonclustered indexes on separate filegroups

If a nonclustered index in the specified filegroup is associated with a table in another filegroup, the index isn't checked because the base table isn't available for validation.

If a table in the specified filegroup has a nonclustered index in another filegroup, the nonclustered index isn't checked because of the following:

  • The base table structure isn't dependent on the structure of a nonclustered index. Nonclustered indexes don't have to be scanned to validate the base table.
  • The DBCC CHECKFILEGROUP command validates objects only in the specified filegroup.

A clustered index and a table can't be on different filegroups; therefore, the previous considerations apply only to nonclustered indexes.

Partitioned tables on separate filegroups

When a partitioned table exists on multiple filegroups, DBCC CHECKFILEGROUP checks the partition rowsets that exist on the specified filegroup and ignores the rowsets in the other filegroups. Informational message 2594 indicates the partitions that weren't checked. Nonclustered indexes not resident on the specified filegroup, aren't checked.

Understand DBCC error messages

After the DBCC CHECKFILEGROUP command finishes, a message is written to the SQL Server error log. If the DBCC command successfully executes, the message indicates a successful completion, and the amount of time that the command ran. If the DBCC command stops before completing the check because of an error, the message indicates the command was terminated, a state value, and the amount of time the command ran. The following table lists and describes the state values that can be included in the message.

State Description
0 Error number 8930 was raised. This indicates a metadata corruption that caused the DBCC command to terminate.
1 Error number 8967 was raised. There was an internal DBCC error.
2 A failure occurred during emergency mode database repair.
3 This indicates a metadata corruption that caused the DBCC command to terminate.
4 An assert or access violation was detected.
5 An unknown error occurred that terminated the DBCC command.

Error reporting

A mini-dump file (SQLDUMP<nnnn>.txt) is created in the SQL Server LOG directory whenever DBCC CHECKFILEGROUP detects a corruption error. When the Feature Usage data collection and Error Reporting features are enabled for the instance of SQL Server, the file is automatically forwarded to Microsoft. The collected data is used to improve SQL Server functionality.

The dump file contains the results of the DBCC CHECKFILEGROUP command and additional diagnostic output. The file has restricted discretionary access-control lists (DACLs). Access is limited to the SQL Server service account and members of the sysadmin role. By default, the sysadmin role contains all members of the Windows BUILTIN\Administrators group and the local administrator's group. The DBCC command doesn't fail if the data collection process fails.

Resolve errors

If any errors are reported by DBCC CHECKFILEGROUP, we recommend restoring the database from the database backup. Repair options can't be specified to DBCC CHECKFILEGROUP.

If no backup exists, running DBCC CHECKDB with a repair option specified corrects the errors reported. The repair option to use is specified at the end of the list if reported errors. Correcting the errors by using the REPAIR_ALLOW_DATA_LOSS option might require that some pages, and therefore data, be deleted.

Result sets

DBCC CHECKFILEGROUP returns the following result set (values may vary):

  • Except when ESTIMATEONLY or NO_INFOMSGS is specified.
  • For the current database, if no database is specified, whether or not any options (except NOINDEX) are specified.
DBCC results for 'master'.
DBCC results for 'sys.sysrowsetcolumns'.
There are 630 rows in 7 pages for object 'sys.sysrowsetcolumns'.
DBCC results for 'sys.sysrowsets'.
There are 97 rows in 1 pages for object 'sys.sysrowsets'.
DBCC results for 'sysallocunits'.
There are 195 rows in 3 pages for object 'sysallocunits'.
  
There are 2340 rows in 16 pages for object 'spt_values'.
DBCC results for 'MSreplication_options'.
There are 2 rows in 1 pages for object 'MSreplication_options'.
CHECKFILEGROUP found 0 allocation errors and 0 consistency errors in database 'master'.
DBCC execution completed. If DBCC printed error messages, contact your system administrator.

If NO_INFOMSGS is specified, DBCC CHECKFILEGROUP returns:

DBCC execution completed. If DBCC printed error messages, contact your system administrator.

If ESTIMATEONLY is specified, DBCC CHECKFILEGROUP returns (values may vary):

Estimated TEMPDB space needed for CHECKALLOC (KB)
-------------------------------------------------
15
  
(1 row(s) affected)
  
Estimated TEMPDB space needed for CHECKTABLES (KB)
--------------------------------------------------
207
  
(1 row(s) affected)
  
DBCC execution completed. If DBCC printed error messages, contact your system administrator.

Permissions

Requires membership in the sysadmin fixed server role or the db_owner fixed database role.

Examples

A. Check the PRIMARY filegroup in the database

The following example checks the primary filegroup of the current database.

DBCC CHECKFILEGROUP;
GO

B. Check the AdventureWorks PRIMARY filegroup without nonclustered indexes

The following example checks the AdventureWorks2022 database primary filegroup (excluding nonclustered indexes) by specifying the identification number of the primary filegroup, and by specifying NOINDEX.

USE AdventureWorks2022;
GO
DBCC CHECKFILEGROUP (1, NOINDEX);
GO

C. Check the PRIMARY filegroup with options

The following example checks the master database primary filegroup and specifies the option ESTIMATEONLY.

USE master;
GO
DBCC CHECKFILEGROUP (1)
WITH ESTIMATEONLY;

See also