This table hint is equivalent to setting the isolation level to SERIALIZABLE. It must wait until session 1 releases its shared range (RangeS-S) locks that SQL Server takes due to the HOLDLOCK table hint. Notice the wait for the exclusive lock for session 2. WHERE resource_database_id = db_id('ExamBook762Ch3') Īlthough your results might vary, especially with regard to identifiers, the DMV returns results similar to the example below. Now let’s use the sys.dm_tran_locks DMV to view some details about the current locks: SELECT In a separate session, start another transaction: BEGIN TRANSACTION In one session, execute the following statements: BEGIN TRANSACTION Let’s start some transactions to observe the locks that SQL Server acquires. The ID for node in the Analytics Platform System (formerly known as Parallel Data Warehouse).įor a full list of subtypes for each resource type, refer to the sys.dm_tran_locks documentation at. Join it with the resource_address column in sys.dm_os_waiting_tasks. The memory address of the internal data structure that is tracking the request. The type of entity that owns the request: TRANSACTION, CURSOR, SESSION, SHARED_TRANSACTION_WORKSPACE, EXCLUSIVE_TRANSACTION_WORKSPACE, or NOTIFICATION_OBJECT. This value changes when the active MARS connection for the transaction changes. The ID of the request for the process that owns the request. The ID of the execution context for the process that owns the request. A deferred recovery transaction has a value of -3. An orphaned distributed transaction has a value of -2. The ID of the session that owns the request. The approximate number of times the requestor has requested the resource. One of the following values to reflect the current status of the request: GRANTED, CONVERT, WAIT, LOW_PRIORITY_CONVERT, LOW_PRIORITY_WAIT, or ABORT_BLOCKERS. The lock mode requested by waiting requests or granted for other requests. The value is 0 for a non-partitioned lock resource. The ID of the lock partition for partitioned lock resource. The ID of the entity with which the resource is associated, such as an object ID, HoBT ID, or Allocation Unit ID. The ID of the database containing the resource.Īdditional information, if available, about the resource not found in other resource columns. If a resource has a subtype, this column displays it. One of the following types of resources: DATABASE, FILE, OBJECT, PAGE, KEY, EXTENT, RID, APPLICATION, METADATA, HOBT, or ALLOCATION_UNIT. Table 3-2 describes each column in sys.dm_tran_locks. It does not provide access to historical information about locks. You can use this DMV only to view information at the current point in time. The sys.dm_tran_locks DMV provides you with information about existing locks and locks that have been requested but not yet granted in addition to details about the resource for which the lock is requested. INSERT INTO Examples.LockingB(RowId, ColumnText) INSERT INTO Examples.LockingA(RowId, ColumnText) LISTING 3-7 Create a test environment for testing locking behavior CREATE TABLE Examples.LockingA Sys.dm_os_wait_stats Use this DMV to see how often processes are waiting while locks are taken.īefore we look at these DMVs in detail, let’s set up our environment as shown in Listing 3-7 so that we can establish some context for locking behavior. Sys.dm_os_waiting_tasks Use this DMV to see which tasks are waiting for a resource. Sys.dm_tran_locks Use this DMV to view all current locks, the lock resources, lock mode, and other related information. You can use the following dynamic management views (DMVs) to view information about locks: As part of the troubleshooting process, you need to determine which resources are locked, why they are locked, and the lock type in effect. Before you can troubleshoot locking issues, you must understand how SQL Server uses locks, which we describe in detail in Skill 3.1.
0 Comments
Leave a Reply. |