SQL Server (TSQL) - Is it possible to EXEC statements in parallel?

Question

SQL Server 2008 R2

Here is a simplified example:

EXECUTE sp_executesql N\'PRINT \'\'1st \'\' + convert(varchar, getdate(), 126) WAITFOR DELAY \'\'000         


        

Answer 1

If after reading all above about potential problems and you still want to run things in parallel, you probably can try sql jobs, put your queries in different jobs, then execute by calling the jobs like this

EXEC msdb..sp_start_job 'Job1'

EXEC msdb..sp_start_job 'Job2' 

Answer 2

Yes, there is a way, see Asynchronous procedure execution.

However, chances are this is not what you need. T-SQL is a data access language, and when you take into consideration transactions, locking and commit/rollback semantics is almost impossible to have a parallel job. Parallel T-SQL works for instance with requests queues, where each requests is independent and there is no correlation between jobs.

What you describe doesn't sound at all like something that can, nor should, actually be paralellized.

Answer 3

SQL Agent Jobs can run in parallel and be created directly from TSQL. The answer by Remus Rusanu contains a link that mentions this along with some disadvantages.

Another disadvantage is that additional security permissions are required to create the job. Also, for the implementation below, the job must run as a specific user+login with additional job management privileges.

It is possible to run the arbitrary SQL as a different (safer) user however I believe it requires sysadmin privilege to designate the job as such.

The returned @pJobIdHexOut can be used to stop the job if needed.

create function Common.ufn_JobIdFromHex(
    @pJobIdBinary binary(16)
    )    
    returns varchar(100) as
/*---------------------------------------------------------------------------------------------------------------------
    Purpose:   Convert the binary represenation of the job_id into the job_id string that can be used in queries 
               against msdb.dbo.sysjobs.

                http://stackoverflow.com/questions/68677/how-can-i-print-a-binary-value-as-hex-in-tsql
                http://stackoverflow.com/questions/3604603 
                MsgBoards

    Modified    By              Description
    ----------  --------------  ---------------------------------------------------------------------------------------
    2014.08.22  crokusek        Initial version, http://stackoverflow.com/questions/3604603 and MsgBoards.
  ---------------------------------------------------------------------------------------------------------------------*/ 
begin 

    -- Convert from binary and strip off the '0x'.
    --
    declare
        @jobIdHex varchar(100) = replace(convert(varchar(300), @pJobIdBinary, 1), '0x', ''); 

    -- The endianness appears to be backwards and there are dashes needed.                
    --
    return
        substring(@jobIdHex,7,2) +
        substring(@jobIdHex,5,2) +
        substring(@jobIdHex,3,2) +
        substring(@jobIdHex,1,2) +
        '-' +
        substring(@jobIdHex,11,2) +
        substring(@jobIdHex,9,2) +
        '-' +
        substring(@jobIdHex,15,2) +
        substring(@jobIdHex,13,2) +
        '-' +
        substring(@jobIdHex,17,4) +
        '-' +
        substring(@jobIdHex,21,12);  
end
go

create proc [Common].[usp_CreateExecuteOneTimeBackgroundJob] 
    @pJobNameKey          varchar(100),     -- Caller should ensure uniqueness to avoid a violation
    @pJobDescription      varchar(1000),
    @pSql                 nvarchar(max),
    @pJobIdHexOut         varchar(100) = null out, -- JobId as Hex string. For SqlServer 2014 binary(16) = varchar(64)
    @pDebug               bit = 0  -- True to include print messages
--
with execute as 'TSqlBackgroundJobOwner' -- requires special permissions (See below)
as
/*---------------------------------------------------------------------------------------------------------------------
    Purpose:  Create a one time background job and launch it immediately.  The job is owned by the "execute as" UserName 

              Caller must ensure the @pSql argument is safe.

Required Permissions for "execute as" user:

        -- User must be created with associated login (w/ deny connect).

        use [msdb];
        create user [$UserName$] for login [$LoginName$];
        alter role [SQLAgentUserRole] add member [$UserName$];
        alter role [SQLAgentReaderRole] add member [$UserName$];
        alter role [SQLAgentOperatorRole] add member [$UserName$];
        grant select on dbo.sysjobs to [$UserName$];
        grant select on dbo.sysjobactivity to [$UserName$];',

        use [Master];
        create user [$UserName$] for login [$LoginName$];
        grant execute on xp_sqlagent_is_starting to [$UserName$];
        grant execute on xp_sqlagent_notify to [$UserName$];';


    Modified    By           Description
    ----------  -----------  ------------------------------------------------------------------------------------------
    2014.08.22  crokusek     Initial version   
    2015.12.22  crokusek     Use the SP caller as the job owner (removed the explicit setting of the job owner).
  ---------------------------------------------------------------------------------------------------------------------*/
begin try       

    declare
        @usp                  varchar(100) = object_name(@@procid),
        @currentDatabase      nvarchar(100) = db_name(),
        @jobId                binary(16),        
        @jobOwnerLogin        nvarchar(100);

    set xact_abort on;    -- ensure transaction is aborted on non-catchables like client timeout, etc.
    begin transaction

        exec msdb.dbo.sp_add_job 
            @job_name=@pJobNameKey,
                @enabled=1, 
                @notify_level_eventlog=0, 
                @notify_level_email=2, 
                @notify_level_netsend=2, 
                @notify_level_page=2, 
                @delete_level=3, 
                @description=@pJobDescription,
                @category_name=N'Database Maintenance',
            -- If not overridden then the the current login is the job owner
            --@owner_login_name=@jobOwnerLogin,  -- Requires sysadmin to set this so avoiding.
            @job_id = @jobId output;

        -- Get the job_id string of the jobId (special format)
        --
        set @pJobIdHexOut = Common.ufn_JobIdFromHex(@jobId);

        if (@pDebug = 1)
        begin
            print 'JobId: ' + @pJobIdHexOut;
            print 'Sql: ' + @pSql;
        end

        exec msdb.dbo.sp_add_jobserver @job_id=@jobId; -- default is local server

        exec msdb.dbo.sp_add_jobstep 
            @job_id=@jobId, 
            @step_name=N'One-Time Job Step 1', 
                @step_id=1, 
            @command=@pSql,
                @database_name=@currentDatabase,
                @cmdexec_success_code=0, 
                @on_success_action=1, 
                @on_fail_action=2, 
                @retry_attempts=0, 
                @retry_interval=0, 
                @os_run_priority=0,
            @subsystem=N'TSQL', 
                @flags=0
            ;

          declare
              @startResult int;                    

          exec @startResult = msdb.dbo.sp_start_job 
              @job_id = @jobId;

      -- End the transaction
      --
      if (@startResult != 0)          
          raiserror('Unable to start the job', 16, 1);  -- causes rollback in catch block
      else
          commit;   -- Success

end try
begin catch
    declare        
        @CatchingUsp  varchar(100) = object_name(@@procid);    

    if (xact_state() = -1)
        rollback;

    --exec Common.usp_Log
    --    @pMethod = @CatchingUsp;

    --exec Common.usp_RethrowError
    --    @pCatchingMethod = @CatchingUsp;
end catch
go

Answer 4

If you want to lock a record so you can execute statements against it, you may want to execute those statements as a transaction.

To execute SQL in parallel, you need to paralellize SQL calls, by executing your SQL from within separate threads/processes in Java, C++, perl, or any other programming language (hell, launching "isql" in shell script in background will work)

Answer 5

It might be worth to check out the article Asynchronous T-SQL Execution Without Service Broker.

Answer 6

You can create an SSIS that has 2 tasks that run in parallel. Then make an unscheduled agent job to call this SSIS. You can finally execute this unscheduled agent job using sp_start_job.