Parallel Processing Using Jobs

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Introduction:

We've all been there. Long queues of reports are piling up, your inbox is full of SQL requests, or end of the month accounting craziness breaks out. The following is a simple way of handling these, mostly uniform, tasks, which usually run in serial fashion.

The idea is simple. Set up a queue, a table which holds the code/stored procedures which need to be executed. Loop over the queue, pick the command value, create a job through dynamic sql and pass all the values (name, command...), which vary from task to task. You then start the job and monitor number of jobs already running before starting a new one (last inner loop involving 'waitfor'). When the job finishes it will automatically self-destruct (@delete_level=3).

Here are the steps we'll follow to handle this.

1. We'll create the 'job queue' and fill it with sample 'waitfor delay' commands with variable wait time using rand() function. The jobs will just simulate the work.

create table #job_queue (id int identity(1,1) primary key,exe_proc varchar(255))
declare @create_job nvarchar(max),@db_name sysname,@job_name varchar(255)
declare @val int,@command nvarchar(max),@delay varchar(16),@i int
set @db_name=db_name()
set @i=1
while @i<=100
    begin
        insert #job_queue values('waitfor delay ''''0:0:'+cast(ceiling(rand()*10) as varchar(3))+'''''')
        set @i=@i+1
    end

2. Starting the main loop. Create the SQL for the job first:

while exists(select 1 from #job_queue)
 begin
  select top 1 @val=id,@command=exe_proc from #job_queue
  set @job_name='_insert_base_job_name_'+cast(@val as varchar(3))
  set @create_job='
  USE [msdb]
  DECLARE @jobId BINARY(16)
  EXEC  msdb.dbo.sp_add_job 
      @job_name='''+@job_name+''',
      @enabled=1,
      @delete_level=3,
      @category_name=N''[Uncategorized (Local)]'',
      @owner_login_name=N''sa''
  EXEC msdb.dbo.sp_add_jobserver 
      @job_name='''+@job_name+''', 
      @server_name = N'''+@@servername+'''
  EXEC msdb.dbo.sp_add_jobstep 
      @job_name='''+@job_name+''', 
      @step_name=N''execute'',
      @step_id=1,
      @cmdexec_success_code=0,
      @on_success_action=1,
      @on_fail_action=2,
      @os_run_priority=0, @subsystem=N''TSQL'',
      @command='''+@command+''',
      @database_name='''+@db_name+''',
      @flags=0
 
  EXEC msdb.dbo.sp_update_job 
      @job_name='''+@job_name+''',
      @enabled=1,
      @start_step_id=1,
      @delete_level=3,
      @category_name=N''[Uncategorized (Local)]'',
      @owner_login_name=N''sa'''

3.Create the job and start it. Then remove the command from the queue:

exec sp_executesql @create_job
exec msdb.dbo.sp_start_job @job_name
delete top (1) #job_queue
print 'starting '+@job_name

4. Monitor number of jobs already running and wait until the number drops under 30 before starting a new one:

while (select count(*) from msdb.dbo.sysjobs_view job
         inner join msdb.dbo.sysjobactivity activity
         on (job.job_id = activity.job_id)
         where run_Requested_date is not null 
         and stop_execution_date is null
         and job.name like  '%_Card360_peter_jobs_%')>=30
  waitfor delay '0:0:2'
 end
drop table #job_queue

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