sp_lock (Transact-SQL)
- Return Code Values. The sp_lock result set contains one row for each lock held by the sessions specified in the @spid1 and @spid2 parameters.
- Remarks. Using SET TRANSACTION ISOLATION LEVEL to specify the level of locking for a session. ...
- Permissions. Requires VIEW SERVER STATE permission. ...
What is SP_lock in SQL Server?
sp_lock. The sp_lock system stored procedure is packaged with SQL Server 2000 and will give you insight into the locks that are happening on your system. This procedure returns much of its information from the syslockinfo in the master database, which is a system table that contains information on all granted, converting, and waiting lock requests.
What is the SP_lock system stored procedure?
The sp_lock system stored procedure is a great tool for checking the amount of locking that occurs on your database system. It returns the number and types of locks that are being held by current active SQL Server sessions. One of my previous articles describes how you can use sp_lock to diagnose problems on your SQL Server.
What is a lock in SQL Server?
SQL Server uses locks, which are objects that the database engine uses to ensure that only one thread can access a resource at a time, to achieve this consistency. Without the use of locks, concurrent data modifications would be possible by separate processes, which could potentially leave the database in an inconsistent state.
How do I lock read operations in SQL Server?
Remarks Users can control the locking of read operations by: Using SET TRANSACTION ISOLATION LEVEL to specify the level of locking for a session. For syntax and restrictions, see SET TRANSACTION ISOLATION LEVEL (Transact-SQL). Using locking table hints to specify the level of locking for an individual reference of a table in a FROM clause.
What is S lock in SQL Server?
SQL Server locking is the essential part of the isolation requirement and it serves to lock the objects affected by a transaction. While objects are locked, SQL Server will prevent other transactions from making any change of data stored in objects affected by the imposed lock.
What is the use of lock in SQL?
Locks are held on SQL Server resources, such as rows read or modified during a transaction, to prevent concurrent use of resources by different transactions. For example, if an exclusive (X) lock is held on a row within a table by a transaction, no other transaction can modify that row until the lock is released.
What is lock in stored procedure?
In a client-side/threading situation, I would solve this by using a lock, having the first user lock the function, the second user encounters the lock, waiting for the result, the first user finishes their procedure call, updates the LatestResult table, and unlocks the second user, who then picks up the result from the ...
What is exclusive lock in SQL Server?
An exclusive lock reserves a page or row for the exclusive use of a single transaction. It is used for DML statements (INSERT, UPDATE, and DELETE) that modify the resource.
What are the types of locks in database?
There are two types of lock:Shared lock:Exclusive lock:Growing phase: In the growing phase, a new lock on the data item may be acquired by the transaction, but none can be released.Shrinking phase: In the shrinking phase, existing lock held by the transaction may be released, but no new locks can be acquired.More items...
How can avoid deadlock in SQL Server?
Useful ways to avoid and minimize SQL Server deadlocks Try to keep transactions short; this will avoid holding locks in a transaction for a long period of time. Access objects in a similar logical manner in multiple transactions. Create a covering index to reduce the possibility of a deadlock.
What is lock table in SQL?
The LOCK TABLE statement allows you to explicitly acquire a shared or exclusive table lock on the specified table. The table lock lasts until the end of the current transaction. To lock a table, you must either be the database owner or the table owner.
Can we check locks in database?
To obtain information about locks in the SQL Server Database Engine, use the sys. dm_tran_locks dynamic management view.
What is lock in database?
A database lock is used to “lock” some data in a database so that only one database user/session may update that particular data. So, database locks exist to prevent two or more database users from updating the same exact piece of data at the same exact time.
What is the difference between a shared lock and an exclusive lock?
The two types are exclusive and shared locks. Exclusive locks can be active or retained; shared locks can only be active (see Active and retained states for locks ).
What are the two authentication modes in SQL Server?
SQL Server supports two authentication modes, Windows authentication mode and mixed mode. Windows authentication is the default, and is often referred to as integrated security because this SQL Server security model is tightly integrated with Windows.
What is trigger in SQL?
A trigger is a special type of stored procedure that automatically runs when an event occurs in the database server. DML triggers run when a user tries to modify data through a data manipulation language (DML) event. DML events are INSERT, UPDATE, or DELETE statements on a table or view.
What is lock in database?
A database lock is used to “lock” some data in a database so that only one database user/session may update that particular data. So, database locks exist to prevent two or more database users from updating the same exact piece of data at the same exact time.
What is no lock in SQL?
The NOLOCK hint allows SQL to read data from tables by ignoring any locks and therefore not get blocked by other processes. This can improve query performance by removing the blocks, but introduces the possibility of dirty reads.
What is the use of lock table query Mcq?
Explanation: Bulk update (BU) locks are used when bulk copying data into a table and either the TABLOCK hint is specified.
What is read lock in MySQL?
MySQL Locks: Read Locks If the session holds the READ lock on a table, they cannot perform a write operation on it. It is because the READ lock can only read data from the table. All other sessions that do not acquire a READ lock are not able to write data into the table without releasing the READ lock.
What happens if you call sp_getapplock multiple times?
If sp_getapplock is called multiple times for the same lock resource, but the lock mode that is specified in any of the requests is not the same as the existing mode, the effect on the resource is a union of the two lock modes. In most cases, this means the lock mode is promoted to the stronger of the lock modes, the existing mode, or the newly requested mode. This stronger lock mode is held until the lock is ultimately released even if lock release calls have occurred before that time. For example, in the following sequence of calls, the resource is held in Exclusive mode instead of in Shared mode.
What is sys.dm_tran_locks?
Use the sys.dm_tran_locks dynamic management view or the sp_lock system stored procedure to examine lock information, or use SQL Server Profiler to monitor locks.
What does SQL Server use to qualify a resource?
SQL Server uses the current database ID to qualify the resource. Therefore, if sp_getapplock is executed, even with identical parameter values on different databases, the result is separate locks on separate resources.
When are locks released?
Locks placed on a resource are associated with either the current transaction or the current session. Locks associated with the current transaction are released when the transaction commits or rolls back. Locks associated with the session are released when the session is logged out. When the server shuts down for any reason, all locks are released.
Can a lock be released with sp_releaseapplock?
Locks can be explicitly released with sp_releaseapplock. When an application calls sp_getapplock multiple times for the same lock resource, sp_releaseapplock must be called the same number of times to release the lock. When a lock is opened with the Transaction lock owner, that lock is released when the transaction is committed or rolled back.
Does a deadlock roll back a transaction?
A deadlock with an application lock does not roll back the transaction that requested the application lock. Any rollback that might be required as a result of the return value must be done manually. Consequently, we recommend that error checking be included in the code so that if certain values are returned (for example, -3), a ROLLBACK TRANSACTION or alternative action is initiated.
Can a member of the database principal acquire application locks that specify that principal?
Only a member of the database principal specified in the @DbPrincipal parameter can acquire application locks that specify that principal. Members of the dbo and db_owner roles are implicitly considered members of all roles.
What is sp_lock stored procedure?
The sp_lock system stored procedure is packaged with SQL Server 2000 and will give you insight into the locks that are happening on your system. This procedure returns much of its information from the syslockinfo in the master database, which is a system table that contains information on all granted, converting, and waiting lock requests.
Why does SQL Server use locks?
SQL Server uses locks, which are objects that the database engine uses to ensure that only one thread can access a resource at a time, to achieve this consistency . Without the use of locks, concurrent data modifications would be possible by separate processes, which could potentially leave the database in an inconsistent state.
How to diagnose database locking issues?
DBAs can effectively diagnose database locking issues by using the SQL Server sp_lock system stored procedure. Tim Chapman outlines what information you can obtain by executing the sp_lock procedure.
What is TechRepublic's free SQL Server newsletter?
TechRepublic's free SQL Server newsletter, delivered each Tuesday, contains hands-on tips that will help you become more adept with this powerful relational database management system.
When you notice a spid that has acquired a large number of database locks, it will be helpful to?
When you notice a spid that has acquired a large number of database locks, it will be helpful to determine what stored procedure or statement is being run. To do this, run the following DBCC command:
Is it a good idea to kill a lock?
In most cases, there is nothing to do but monitor the system. It's not a good idea to kill a process because it has a large number of locks in the system, unless you are absolutely certain that nothing else is adversely affected. Instead, you should think of ways to automate the analyzation of your locking situation.
Is sp_lock self explanatory?
On my system, here's what the procedure returns. The information returned from sp_lock isn't self explanatory and will require some investigation to get to the meaningful data. However, you have the luxury to copy the text of this stored procedure and create a new one that will give you a better explanation as to what is going on in the system. (In this article, we will focus only on the data returned by sp_lock.)
Why is SQL Server locking important?
Locking is essential to successful SQL Server transactions processing and it is designed to allow SQL Server to work seamlessly in a multi-user environment. Locking is the way that SQL Server manages transaction concurrency. Essentially, locks are in-memory structures which have owners, types, and the hash of the resource that it should protect.
What happens when SQL Server locks objects?
While objects are locked, SQL Server will prevent other transactions from making any change of data stored in objects affected by the imposed lock. Once the lock is released by committing the changes or by rolling back changes to initial state, other transactions will be allowed to make required data changes.
What does "wait" mean in SQL?
Translated into the SQL Server language, this means that when a transaction imposes the lock on an object, all other transactions that require the access to that object will be forced to wait until the lock is released and that wait will be registered with the adequate wait type.
What is the locking hierarchy in SQL Server?
SQL Server has introduced the locking hierarchy that is applied when reading or changing of data is performed. The lock hierarchy starts with the database at the highest hierarchy level and down via table and page to the row at the lowest level
How big is a lock in SQL Server?
A lock as an in-memory structure is 96 bytes in size. To understand better the locking in SQL Server, it is important to understand that locking is designed to ensure the integrity of the data in the database, ...
What is the importance of isolation in SQL Server?
Isolation – requires that a transaction that is still running and did not commit all data yet, must stay isolated from all other transactions. Dur ability – requires that committed data must be stored using method that will preserve all data in correct state and available to a user, even in case of a failure. SQL Server locking is the essential part ...
What is exclusive lock?
Exclusive lock (X) – This lock type, when imposed, will ensure that a page or row will be reserved exclusively for the transaction that imposed the exclusive lock, as long as the transaction holds the lock.
What is sp_who2?
sp_who2 is a undocumented thus unsupported stroed procedure in SQL server, but widely used inststed of sp_who to list processes currently active in SQL Server. Both these procudures are designed to retrive same result set, however sp_who2 adds some extra columns which sp_who does not include. Furthermore, sp_who2 makes an effort to make the display to be as compact as possible for output in text mode.
What is the result set of sp_who2?
The result set of sp_who2 will contains a column named BlkBy, this represents the SPID that is currently stopping the SPID in the row.
What is sys.dm_tran_locks?
and it is recommended to use sys.dm_tran_locks instead. This dynamic management object returns information about currently active lock manager resources. Each row represents a currently active request to the lock manager for a lock that has been granted or is waiting to be granted.
Where is the activity monitor in SSMS?
For example, SSMS 2008 and 2012 have it in the context menu when you right-click on a server node.
When does transaction isolation change?
Once you change the transaction isolation level it only changes when the scope exits at the end of the procedure or a return call , or if you change it explicitly again using SET TRANSACTION ISOLATION LEVEL.
Can you have orphaned transactions holding exclusive locks?
You can have orphaned distributed transactions holding exclusive locks and you will not see them if your script assumes there is a session associated with the transaction (there isn't!). Run the script below to identify these transactions:
Does SP_LOCK return more details?
It generally returns more details in more user friendly syntax then sp_lock does.
Can you have multiple nested stored procedures?
In addition the TRANSACTION ISOLATION LEVEL is only scoped to the stored procedure, so you can have multiple nested stored procedures that execute at their own specific isolation levels.
Is Xclusive Lock misleading?
NB the [Xclusive lock for command] column can be misleading -- it shows the current command for that spid; but the X lock could have been triggered by an earlier command in the transaction.
