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Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance


Attribute Value
Product Name SQL Server
Event ID 1204
Component SQLEngine
Symbolic Name LK_OUTOF
Message Text The instance of the SQL Server Database Engine cannot obtain a LOCK resource at this time. Rerun your statement when there are fewer active users. Ask the database administrator to check the lock and memory configuration for this instance, or to check for long-running transactions.


During execution, queries frequently acquire and release locks on the resources they access. Acquiring a lock uses up the lock structures from an available pool of lock structures. When new locks can't be acquired because there are no more lock structures available in the pool, the error 1204 message is returned. This issue can be due to any of the following reasons:

  • SQL Server can't allocate more memory, either because other processes are using it, or because SQL Server has used up all of its memory and reached the value configured using the configuration option max server memory.

  • The lock manager can't use more than 60 percent of the memory available to SQL Server, and the threshold has already been met.

  • You set up the configuration option locks of the system stored procedure sp_configure (Transact-SQL) to a non-default, non-dynamic value.

  • You enabled Trace Flags 1211, 1224, or both on your SQL Server to control lock escalation behavior, and you're executing queries that require many locks.

User action

  • If you suspect that SQL Server can't allocate sufficient memory, try the following options:

    • Identify if any other memory clerk inside SQL Server has used a large part of the SQL Server configured memory, by using a query like the following one:

      SELECT pages_kb, type, name, virtual_memory_committed_kb, awe_allocated_kb
      FROM sys.dm_os_memory_clerks
      ORDER BY pages_kb DESC;

      Then reduce the memory consumption of that memory clerk to allow for lock memory to use more resources. For more information, see Troubleshoot out of memory or low memory issues in SQL Server.

    • If applications besides SQL Server are consuming resources, try stopping these applications or consider running them on a separate server. This releases memory from other processes for SQL Server.

    • If you configured max server memory, increase the max server memory setting.

  • If you suspect that the lock manager used the maximum amount of available memory, identify the transaction that is holding the most locks and terminate it. The following script identifies the transaction that has the most locks:

    SELECT request_session_id, COUNT (*) num_locks
    FROM sys.dm_tran_locks
    GROUP BY request_session_id
    ORDER BY count (*) DESC;

    Take the highest session ID, and terminate it by using the KILL command.

  • If you're using a non-default value for locks, use sp_configure to change the value of locks to its default setting by using the following statement:

    EXEC sp_configure 'locks', 0;
  • If you encountered the above error message when using the SQL Server trace flags 1211, 1224, or both, review their use and disable them while executing queries that require a large number of locks. For more information, review DBCC TRACEON - Trace Flags (Transact-SQL) and Resolve blocking problems caused by lock escalation in SQL Server.