Ter, 27 de Abril de 2010 01:22
Última atualização em Ter, 27 de Abril de 2010 01:25
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 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:
DBCC TRACEON (3604)
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.
Undocumented DBCC commands
Here you can find some useful undocumented DBCC commands.
1. DBCC BUFFER
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
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
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This is the example:
DBCC TRACEON (3604)
dbcc buffer(master,'sysobjects')
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2. 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
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This is the example:
DBCC TRACEON (3604)
dbcc bytes (10000000, 100)
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3. DBCC DBINFO
Displays DBINFO structure for the specified database.
Syntax:
DBCC DBINFO [( dbname )]
where
dbname - is the database name.
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This is the example:
DBCC TRACEON (3604)
DBCC DBINFO (master)
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4. DBCC DBTABLE
This command displays the contents of the DBTABLE structure.
Syntax:
DBCC DBTABLE ({dbid|dbname})
where
dbid|dbname - database name or database ID
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This is the example:
DBCC TRACEON (3604)
DBCC DBTABLE (master)
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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
5. DBCC DES
Prints the contents of the specified DES (descriptor).
Syntax:
dbcc des [( [dbid|dbname] [,objid|objname] )]
where
dbid|dbname - database id|database name.
objid|objname - object id|object name
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This is the example:
DBCC TRACEON (3604)
DBCC DES
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6. DBCC HELP
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 the example:
DBCC TRACEON (3604)
DECLARE @dbcc_stmt sysname
SELECT @dbcc_stmt = 'CHECKTABLE'
DBCC HELP (@dbcc_stmt)
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7. DBCC IND
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|database name.
objid|objname - object id|object name
printopt - print option
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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 the example:
DBCC TRACEON (3604)
DBCC IND (master, sysobjects, 0)
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8. DBCC log
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}] )
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, 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
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To view the transaction log for the master database, run the following command:
DBCC log (master)
9. DBCC PAGE
You can use this command to view the data page structure.
Syntax:
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.
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This is the example:
DBCC TRACEON (3604)
DBCC PAGE (master, 1, 1)
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Look at here for more details:
Data page structure in MS SQL 6.5
10. DBCC procbuf
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|database name.
objid|objname - object id|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)
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This is the example:
DBCC TRACEON (3604)
DBCC procbuf(master,'sp_help',1,0)
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11. 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
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This is the 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)
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12. DBCC pss
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)
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This is the example:
DBCC TRACEON (3604)
dbcc pss
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13. DBCC resource
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 the example:
DBCC TRACEON (3604)
DBCC resource
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14. 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
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This is the 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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fonte: mssqlcity
