SQL Server 6.5: Some Useful Undocumented DBCC Commands

Introduction

In this article I want to tell you about some useful undocumented
DBCC commands, and how you can use these commands in SQL Server 6.5
for administering and monitoring.

DBCC is an abbreviation of a DataBase Consistency Checker.
This is the description of DBCC from SQL Server Books Online:


Statement used to check the logical and physical consistency of a
database, check memory usage, decrease the size of a database, check
performance statistics, and so on. DBCC helps ensure the physical and
logical consistency of a database, but it is not corrective.

Undocumented DBCC commands

1. DBCC allocdump 

This command can be used to display all extents on an allocation page.

Syntax:


DBCC allocdump( dbid, page )




where
  dbid - is the database id
  page - is the allocation page number

Example:


DBCC TRACEON (3604)
DECLARE @dbid int, @pageid int
SELECT @dbid = DB_ID('pubs')
SELECT @pageid = first FROM sysindexes WHERE
  id = object_id('titleauthor') AND indid = 1
DBCC allocdump(@dbid, @pageid)




2. DBCC bhash 

This command can check integrity of and optionally print the buffer hash 
table.

Syntax:


DBCC bhash( { print_bufs | no_print }, bucket_limit )




where
  print_bufs   - display all buffers (default)
  no_print     - display only buffers with problems
  bucket_limit - number of buffers allowed in a bucket (default = 0)

Example:


DBCC TRACEON (3604)
DBCC bhash




3. DBCC buffer 

This command can be used to print buffer headers and pages from the
buffer cache.

Syntax:


DBCC buffer([dbid|dbname][,objid|objname][,nbufs], printopt = 
{0|1|2},buftype)




where
  dbid|dbname   - database name or database ID
                  (0 will show data for all databases)
  objid|objname - object ID or object name
                  (0 will show data for all objects)
  nbufs         - number of buffers to examine
  printopt      - print option
                  0  print out only the buffer header and page header 
(default)
                  1  print out each row separately and the offset table
                  2  print out each row as a whole and the offset table
  buftype       - buffer type to print

Example:


DBCC TRACEON (3604)
dbcc buffer(0,'sysobjects')




4. DBCC bytes 

This command can be used to dump out bytes from a specific address.

Syntax:


DBCC bytes( startaddress, length )




where
  startaddress  - starting address to dump
  length        - number of bytes to dump

Example:


DBCC TRACEON (3604)
dbcc bytes (1000000, 100)




5. DBCC DBINFO 

Print DBINFO structure for a specified database.

Syntax:


DBCC DBINFO [( dbname )]




where
  dbname - is the database name.

Example:


DBCC TRACEON (3604)
DBCC DBINFO (pubs)




6. DBCC DBTABLE 

This command prints out the contents of the DBTABLE structure.

Syntax:


DBCC DBTABLE ({dbid|dbname})




where
  dbid|dbname  - database name or database ID

Example:


DBCC TRACEON (3604)
DBCC DBTABLE (pubs)




The DBTABLE structure has an output parameter called dbt_open.
This parameter keeps track of how many users are in the database.

Look at here for more details:
FIX: 
Database Usage Count Does Not Return to Zero

7. DBCC delete_row 

This command can be used to delete an index or data row by either
a row number or an offset on a page. DBCC delete_row is the nonloged
command, so you can delete particular row without placed this row into
transactional log. Use this command at your own risk!

Syntax:


DBCC delete_row ( dbid|dbname, page, delete_by_row, rownum )




where
  dbid|dbname    - database ID or database name
  page           - logical page number
  delete_by_row  - how delete: by row or by offset
                   (1 - the next parameter is row number)
                   (0 - the next parameter is offset on the page)
  rownum         - row number or offset

Example:


SET NOCOUNT ON
GO
USE pubs
GO
DBCC TRACEON (3604)
GO
DECLARE @pgid int
SELECT COUNT(*) FROM titleauthor
SELECT @pgid = first FROM sysindexes WHERE
  id = object_id('titleauthor') AND indid = 1
SELECT xactid AS TRAN_ID, op AS LOG_RECORD FROM syslogs
DBCC delete_row (pubs, @pgid, 'row', 1)
SELECT xactid AS TRAN_ID, op AS LOG_RECORD FROM syslogs
SELECT COUNT(*) FROM titleauthor




8. DBCC des 

This command used to print the contents of the specified DES (descriptor).

Syntax:


DBCC des( [ dbid|dbname ][, objid ] )




where
  dbid|dbname - database ID or database name
  objid       - object ID

Example:


DBCC TRACEON (3604)
DBCC DES




9. DBCC extentchain 

This command shows extent header info for all extents in use by
the specified object.

Syntax:


DBCC extentchain(dbid,objid,indexid,sort={1|0},display={1|0} [,order={1|0}])




where
  dbid     - database ID
  objid    - object ID
  indexid  - index ID
  sort     - report on state of the sort bit
             (0  don't include this info)
             (1  do report on sort bit status)
  display  - what to report
             (0  display the count only)
             (1  display the extents)
  order    - (optional) order to follow the chain
             (0  descending, 1  ascending)

Example:


DBCC TRACEON (3604)
DECLARE @dbid int, @objectid int
SELECT @dbid = DB_ID('pubs')
SELECT @objectid = object_id('authors')
dbcc extentchain(@dbid,@objectid,0,0,0,0)




10. DBCC extentcheck 

This command has the same output as extentchain and examine all extents
on allocation pages for specified object.

Syntax:


DBCC extentcheck( dbid, objid, indexid, sort = {1|0} )




where
  dbid    - database ID
  objid   - object ID
  indexid - index ID
  sort    - state of the sort bit
            (0  don't report this, 1  report sort bit status)

Example:


DBCC TRACEON (3604)
DECLARE @dbid int, @objectid int
SELECT @dbid = DB_ID('pubs')
SELECT @objectid = object_id('authors')
dbcc extentcheck(@dbid,@objectid,0,1)




11. DBCC extentdump 

This command shows an extent dump.

Syntax:


DBCC extentdump( dbid, page )




where
  dbid  - database ID
  page  - the number of a page controlled by the extent in question

Example:


DBCC TRACEON (3604)
DECLARE @dbid int
SELECT @dbid = DB_ID('pubs')
DBCC extentdump(@dbid, 1)




12. DBCC extentzap 

This command can be used to clear all extents matching the parameter values.

Syntax:


DBCC extentzap( dbid, objid, indexid, sort )




where
  dbid    - database ID
  objid   - object ID
  indexid - index ID
  sort    - state of the sort bit

Example:


DBCC TRACEON (3604)
DECLARE @dbid int, @objectid int
SELECT @dbid = DB_ID('pubs')
SELECT @objectid = object_id('authors')
DBCC extentzap(@dbid,@objectid,0,0)




13. DBCC findnotfullextents 

This command shows extend id of extents allocated to the specified
objid that are not full. If objid is specified, then an indexid
can be specified, or all will do all of the indexes of table.
If objid is all, then all database tables are done.

Syntax:


DBCC findnotfullextents( dbid,objid,indexid, sort = {1|0} )




where
  dbid    - database ID
  objid   - object ID
  indexid - index ID
  sort    - state of the sort bit

Example:


DBCC TRACEON (3604)
DECLARE @dbid int, @objectid int
SELECT @dbid = DB_ID('pubs')
SELECT @objectid = object_id('authors')
DBCC findnotfullextents(@dbid,@objectid,0,0)




14. DBCC HELP 

DBCC HELP returns syntax information for the specified DBCC statement.

Syntax:


DBCC HELP ('dbcc_statement' | @dbcc_statement_var | '?')




This is the example:


DBCC TRACEON (3604)
DECLARE @dbcc_stmt sysname
SELECT @dbcc_stmt = 'CHECKTABLE'
DBCC HELP (@dbcc_stmt)




Look at here for more details:
DBCC HELP 
(T-SQL)

15. DBCC ind 

This command shows all pages in use by indexes of the specified tabname.

Syntax:


DBCC ind( dbid|dbname, objid, printopt = { 0 | 1 | 2 } )




where
  dbid|dbname - database ID or database name
  objid       - object ID
  printopt    - print option
            (0  print out only the buffer header and page header (default)
             1  print page headers, page data in row format, and offset 
tables
             2  print page headers, unformatted page data, and offset 
tables)

Example:


DBCC TRACEON (3604)
declare @obid int
SELECT @obid = object_id('authors')
DBCC ind (pubs, @obid, 1)




16. DBCC locateindexpgs 

This command prints all references in the index to the specified page.

Syntax:


DBCC locateindexpgs( dbid, objid, page, indexid, level )




where
  dbid    - database ID
  objid   - object ID
  page    - logical page number of the page for which index
            references are being searched
  indexid - index ID
  level   - level within the index to search for references

Example:


DBCC TRACEON (3604)
DECLARE @dbid int, @objectid int
SELECT @dbid = DB_ID('pubs')
SELECT @objectid = object_id('authors')
DBCC locateindexpgs(@dbid,@objectid,1,1,0)




17. DBCC lock 

This command can be used to print out lock chains.

Syntax:


DBCC lock




Example:


DBCC TRACEON (3604)
DBCC lock




18. DBCC log 

This command is used to view the transactional log for the specified
database.


DBCC log ( {dbid|dbname}, [, type={0|1|2|3|4}] )




PARAMETERS:
   Dbid or dbname - Enter either the dbid or the name of the database
                    in question.

      type - is the type of output:

      0 - minimum information (operation, context, transaction id)

      1 - more information (plus flags, tags, row length)

      2 - very detailed information (plus object name, index name,
          page id, slot id)

      3 - full information about each operation

      4 - full information about each operation plus hexadecimal dump
          of the current transaction log's row.

by default type = 0

To view the transaction log for the master database, you can run the
following command:


DBCC log (master)




19. DBCC PAGE 

You can use this command to view the data page structure.


DBCC PAGE ({dbid|dbname}, pagenum [,print option] [,cache] [,logical])




PARAMETERS:
   Dbid or dbname - Enter either the dbid or the name of the database
                    in question.

   Pagenum - Enter the page number of the SQL Server page that is to
             be examined.

   Print option - (Optional) Print option can be either 0, 1, or 2.

                  0 - (Default) This option causes DBCC PAGE to print
                      out only the page header information.
                  1 - This option causes DBCC PAGE to print out the
                      page header information, each row of information
                      from the page, and the page's offset table. Each
                      of the rows printed out will be separated from
                      each other.
                  2 - This option is the same as option 1, except it
                      prints the page rows as a single block of
                      information rather than separating the
                      individual rows. The offset and header will also
                      be displayed.

   Cache - (Optional) This parameter allows either a 1 or a 0 to be
           entered.
           0 - This option causes DBCC PAGE to retrieve the page
               number from disk rather than checking to see if it is
               in cache.
           1 - (Default) This option takes the page from cache if it
               is in cache rather than getting it from disk only.

   Logical - (Optional) This parameter is for use if the page number
             that is to be retrieved is a virtual page rather then a
             logical page. It can be either 0 or 1.

             0 - If the page is to be a virtual page number.
             1 - (Default) If the page is the logical page number.

In this example one data page is viewed from the table titleauthor,
database pubs.


USE pubs
GO
DBCC TRACEON (3604)
GO
DECLARE @pgid int
SELECT @pgid = first FROM sysindexes WHERE
  id = object_id('titleauthor') AND indid = 1
DBCC PAGE (pubs, @pgid, 1)
GO




This is the result from my computer:


...

DATA:
Offset 32 -
011e9820:  04042000 3137322d 33322d31 31373650  .. .172-32-1176P
011e9830:  53333333 33016400 0000051a 16150f04  S3333.d.........
...




Look at here for more details:
Data 
page structure in MS SQL 6.5

20. DBCC pglinkage 

This command can be used to display the page chain, performing
integrity checks during traversal.

Syntax:


DBCC pglinkage(dbid,start,number,printopt={0|1|2},target,order={1|0})




where
  dbid     - database ID
  start    - page number with which to start
  number   - number of pages to examine, or 0 if target is specified
  printopt - print option
             (0  display only the count of pages scanned
              1  display information about the last 16 pages scanned
              2  display all page numbers in the scan)
  target   - the particular page we are looking for
  order    - traversal order
             (0  descending, 1  ascending)

Example:


DBCC TRACEON (3604)
DBCC pglinkage(6,26,0,1,0,1)




21. DBCC procbuf 

This command prints procedure buffer headers and proc-headers from
the procedure cache.

Syntax:


DBCC procbuf( [dbid], [objid], [nbufs], [printopt = {0|1}] )




where
  dbid     - database ID
  objid    - object ID
  nbufs    - number of buffers to print
  printopt - print option
             (0  print out only the proc buff and proc header (default)
              1  print out proc buff, proc header and contents of buffer)

Example:


DBCC TRACEON (3604)
DECLARE @dbid int, @objectid int
SELECT @dbid = DB_ID('master')
SELECT @objectid = object_id('sp_help')
DBCC procbuf(@dbid,@objectid,1,0)




22. DBCC prtipage 

This command prints the page number pointed to by each row on the
specified index page.

Syntax:


DBCC prtipage( dbid, objid, indexid, indexpage )




where
  dbid      - database ID
  objid     - object ID
  indexid   - index ID
  indexpage - the logical page number of the index page to dump

Example:


DBCC TRACEON (3604)
DECLARE @dbid int, @objectid int
SELECT @dbid = DB_ID('pubs')
SELECT @objectid = object_id('authors')
DBCC prtipage(@dbid,@objectid,1,0)




23. DBCC pss 

This command shows info about processes currently connected to the
dataserver. Structure is the source of data contained in the sysprocesses
table.

Syntax:


DBCC pss( suid, spid, printopt = { 1 | 0 } )




where
  suid     - server user ID
  spid     - server process ID
  printopt - print option
             (0  standard output,
              1  all open DES's and current sequence tree)

Example:


DBCC TRACEON (3604)
dbcc pss




24. DBCC rebuildextents 

DBCC rebuildextents rebuilds an object's extent chain.
You should set READ ONLY option for your database, before run this command.

Syntax:


DBCC rebuildextents( dbid, objid, indexid )




where
  dbid    - database ID
  objid   - object ID
  indexid - index ID

Example:


DBCC TRACEON (3604)
DECLARE @dbid int, @objectid int
SELECT @dbid = DB_ID('pubs')
SELECT @objectid = object_id('authors')
DBCC rebuildextents(@dbid,@objectid,1)




25. DBCC resource 

This command shows dataserver level RESOURCE, PERFMON and DS_CONFIG
info. RESOURCE shows addresses of various data structures used by
the server. PERFMON structure contains master..spt_monitor
field info. DS_CONFIG structure contains master..syscurconfigs
field info.

Syntax:


DBCC resource




Example:


DBCC TRACEON (3604)
DBCC resource




26. DBCC show_bucket 

This command shows hash bucket info for the specified pageid.

Syntax:


DBCC show_bucket( dbid|dbname, pageid, lookup_type )




where
  dbid|dbname - database ID or database name
  page        - logical page number of page being looked for
  lookup_type - how to conduct search
          (1  use hash algorithm to look in the bucket the page should be in
           2  scan the entire buffer cache)

Example:


DBCC TRACEON (3604)
DBCC show_bucket (pubs, 1, 1)




27. DBCC TAB 

You can use the following undocumented command to view the data
pages structure (in comparison with DBCC PAGE, this command will
return information about all data pages for viewed table, not
only for particular number):


DBCC tab (dbname, objname, printopt={ 0 | 1 | 2 })




where dbname - is the database name,
      objname - is the table name,
      printopt - is the type of the output:

      0 - minimum information (only the pages headers, the total
          number of data pages in this table and the total number
          of data rows in this table)

      1 - more information (plus full rows structure)

      2 - as printopt = 1, but without rows separation (full dump)

by default printopt = 0

Example:


DBCC TRACEON (3604)
DBCC tab (pubs, 'authors')




28. DBCC undo 

Syntax:


DBCC undo( dbid, pageno, rowno )

Literature

1. "What are all the dbcc commands for SQL Server?" NTFAQ
   http://www.ntfaq.com/Articles/Index.cfm?ArticleID=14186

2. INFO: Description of DBCC PAGE Command
   http://support.microsoft.com/support/kb/articles/Q83/0/65.ASP

3. THE UNAUTHORIZED DOCUMENTATION OF DBCC
   http://user.icx.net/~huntley/dbccinfo.htm

4. The Totally Unauthorized List of Sybase DBCC Commands
   http://www.kaleidatech.com/dbcc1.htm

5. The Totally Unauthorized List of Sybase DBCC Commands
   http://www.kaleidatech.com/dbcc2.htm

6. The Totally Unauthorized List of Sybase DBCC Commands
   http://www.kaleidatech.com/dbcc3.htm

7. FIX: Database Usage Count Does Not Return to Zero
   http://support.microsoft.com/support/kb/articles/Q175/3/03.ASP

8. DBCC HELP (T-SQL)
   http://msdn.microsoft.com/library/psdk/sql/dbcc_10.htm

9. INFO: Description of the DBCC PGLINKAGE Command
   http://support.microsoft.com/support/kb/articles/Q83/1/15.ASP