A hard disk drive can be divided into multiple logical partitions. Primary partition is a partition that contains the operating system and is used for booting the computer. Only the primary partition can be marked as an active partition. The computer hardware looks for the boot files on the active partition to start loading the operating system.
A partition function maps the rows of a table or an index to partitions that are based on the values of a column. SQL Server 2005 places the rows in the left-most partition if their partitioning column has null values. The partition function is created using the CREATE PARTITION FUNCTION statement. This function is created before creating a partition scheme.
A partition scheme maps the partitions of a partitioned table or index to filegroups. These partitions are identified by a partition function. The CREATE PARTITION SCHEME statement is used to create a partition scheme. A partition scheme can be created only after creating a partition function by using the CREATE PARTITION FUNCTION statement.
A disk partition which does not have any file system or is unformatted is referred to as a raw partition. In some scenarios, raw partitions might give a slight performance enhancement compared to having a file system. However, a raw partition is discouraged by Microsoft because raw partitioning limits the common data access and recovery options that NTFS provides.
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The DBCC INPUTBUFFER statement is used to display the last statement sent from a client to an instance of Microsoft SQL Server. It has the following syntax: DBCC INPUTBUFFER ( session_id [ , request_id ] ) [WITH NO_INFOMSGS] where,
session_id is the session ID connected with each active primary connection.
request_id is the exact request (batch) that has to be searched within the current session.
WITH allows for options to be specified.
NO_INFOMSGS suppresses all informational messages whose severity level is from 0 to 10.
The DBCC OUTPUTBUFFER statement is used to return the current output buffer in ASCII and hexadecimal format for the specified session_id. It has the following syntax: DBCC OUTPUTBUFFER ( session_id [ , request_id ] ) [ WITH NO_INFOMSGS ] where,
session_id is the session ID connected with each active primary connection.
request_id is the exact request (batch) that has to be searched within the current session.
WITH allows for options to be specified.
NO_INFOMSGS suppresses all informational messages whose severity level is from 0 to 10.
The following example returns the current output buffer information for an assumed session ID of 48. DBCC OUTPUTBUFFER (48);
Trace flags are used to diagnose performance issues or debug stored procedures. Trace flags are of the following two types:
Session: Session trace flags are active only for a specified connection. A trace flag enabled in a session does not disturb the trace flag opened in another session.
Global: Global trace flags are set at server level and are visible to every connection. Some of the flags can be enabled at global level, whereas others can be enabled at global or session levels.
Trace flags can be enabled by using the DBCC TRACEON stored procedure, and disabled by using the DBCC TRACEOFF stored procedure. The status of a trace flag can be displayed by using the DBCC TRACESTATUS stored procedure.
The EXECUTE AS clause is used to set the execution context of a session. By default, a session begins when a user logs in and ends when he logs off. All operations are subject to permission checks against that user during a session. When an EXECUTE AS statement is executed, the execution context of the session is switched to a particular user name or login. After the context switch, permissions are checked against the user and login security tokens for that account instead of the individual calling the EXECUTE AS clause. To specify the EXECUTE AS clause on a login and a database user, the caller must have IMPERSONATE permissions on the specified login name and the specified user name, respectively.
The sp_who stored procedure is used to get information about user login, hostname, and system process id of a blocking process and other processes. It gives information only about current users and processes in an instance of the Microsoft SQL Server Database Engine. The information can be filtered to return only those processes that are not idle, that belong to a specific session, or that belong to a specific user. It has the following syntax: sp_who [ [ @loginame = ] ‘login’ | session ID | ‘ACTIVE’ ] where,
[ @loginame = ] ‘login’ | session ID | ‘ACTIVE’ is used to filter the result set.
login is sysname that identifies processes belonging to a particular login.
session ID is a session identification number that belongs to the SQL Server instance.
ACTIVE excludes sessions that are waiting for the next command from the user.