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In this article, I want to tell you about some useful undocumented DBCC commands, and how you can use these commands in SQL Server 7.0 and 2000 for administering and monitoring.
DBCC is an abbreviation for Database Console Command. DBCC commands are generally used to check the physical and logical consistency of a database, although they are also used for a variety of miscellaneous tasks, as you will see here.
Note, the command: |
| is issued before each of the following DBCC examples in order to better demonstrate the effects of the command by displaying a trace of the output of the DBCC command. It is not actually required to run the DBCC commands examined below. If you run any of the DBCC commands below without the above option, the command runs, but you don't see what it is doing. |
This command can be used to display buffer headers and pages from the buffer cache.
Syntax:
dbcc buffer ([dbid|dbname] [,objid|objname] [,nbufs], [printopt])
where:
dbid|dbname - database id|database name
objid|objname - object id|object name
nbufs - number of buffers to examine
printopt - print option, which includes:
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
This is an example:
DBCC TRACEON (3604)
DBCC buffer(master,'sysobjects') |
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
This is an example:
DBCC TRACEON (3604)
DBCC bytes (10000000, 100) |
Displays DBINFO structure for the specified database.
Syntax:
DBCC DBINFO [(dbname)]
where:
dbname - is the database name
This is an example:
DBCC TRACEON (3604)
DBCC DBINFO (master) |
This command displays the contents of the DBTABLE structure.
Syntax:
DBCC DBTABLE ({dbid|dbname})
where:
dbid|dbname - database name or database ID
This is an example:
DBCC TRACEON (3604)
DBCC DBTABLE (master)
The DBTABLE structure has an output parameter called dbt_open. This parameter keeps track of how many users are in the database. |
Prints the contents of the specified DES (descriptor).
Syntax:
dbcc des [([dbid|dbname] [,objid|objname])]
where:
dbid|dbname - database id or the database name
objid|objname - object id or the object name
This is an example:
DBCC TRACEON (3604)
DBCC DES |
DBCC HELP returns syntax information for the specified DBCC statement. In comparison with DBCC HELP command in version 6.5, it returns syntax information only for the documented DBCC commands.
Syntax:
DBCC HELP ('dbcc_statement' | @dbcc_statement_var | '?')
This is an example:
DBCC TRACEON (3604)
DECLARE @dbcc_stmt sysname
SELECT @dbcc_stmt = 'CHECKTABLE'
DBCC HELP (@dbcc_stmt) |
Shows all pages in use by indexes of the specified table.
Syntax:
dbcc ind(dbid|dbname, objid|objname, printopt = {-2|-1|0|1|2|3})
where:
dbid|dbname - database id or the database name
objid|objname - object id or the object name
printopt - print option
There is change in this command in how it is used in SQL Server 7.0, in that the printopt parameter is now no longer optional.
This is an example:
DBCC TRACEON (3604)
DBCC IND (master, sysobjects, 0) |
This command is used to view the transaction log for the specified database.
Syntax:
DBCC log ({dbid|dbname}, [, type={-1|0|1|2|3|4}])
where:
dbid or dbname - Enter either the dbid or the name of the database
type - is the type of output, and includes these options:
0 - minimum information (operation, context, transaction id)
1 - more information (plus flags, tags, row length, description)
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.
-1 - full information about each operation plus hexadecimal dump of the current transaction log's row, plus Checkpoint Begin, DB Version, Max XDESID
by default, type = 0
To view the transaction log for the master database, run the following command:
DBCC log (master) |
You can use this command to view the data page structure.
Syntax:
DBCC PAGE ({dbid|dbname}, pagenum [,print option] [,cache] [,logical])
where:
dbid|dbname - Enter either the dbid or the name of the database
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.
This is an example:
DBCC TRACEON (3604)
DBCC PAGE (master, 1, 1) |
This command displays procedure buffer headers and stored procedure headers from the procedure cache.
Syntax:
DBCC procbuf([dbid|dbname], [objid|objname], [nbufs], [printopt = {0|1}])
where:
dbid|dbname - database id or the database name
objid|objname - object id or the object name
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)
This is an example:
DBCC TRACEON (3604)
DBCC procbuf(master,'sp_help',1,0) |
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
This is an example:
DBCC TRACEON (3604)
DECLARE @dbid int, @objectid int
SELECT @dbid = DB_ID('master')
SELECT @objectid = object_id('sysobjects')
DBCC prtipage(@dbid,@objectid,1,0) |
This command shows info about processes currently connected to the server.
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)
This is an example:
DBCC TRACEON (3604)
DBCC pss |
This command shows the server's level RESOURCE, PERFMON and DS_CONFIG information. 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 information.
Syntax:
DBCC resource
This is an example:
DBCC TRACEON (3604)
DBCC resource
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)
Syntax:
DBCC tab (dbid, objid)
where:
dbid - is the database id
objid - is the table id
This is an example:
DBCC TRACEON (3604)
DECLARE @dbid int, @objectid int
SELECT @dbid = DB_ID('master')
SELECT @objectid = object_id('sysdatabases')
DBCC TAB (@dbid,@objectid)
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Submitted By :
Nayan Patel
(Member Since : 5/26/2004 12:23:06 PM)
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Job Description :
He is the moderator of this site and currently working as an independent consultant. He works with VB.net/ASP.net, SQL Server and other MS technologies. He is MCSD.net, MCDBA and MCSE. In his free time he likes to watch funny movies and doing oil painting. |
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(Birth Date : 7/14/1981 ) |
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