Tuesday, August 23, 2016

Auto Trap

My employer is fairly liberal in allowing reasonably competent folks direct access to SSMS for querying into our databases. This approach encourages folks to learn the structure of the data for themselves, and to answer most of the ad hoc work they might otherwise need to investigate. The disadvantage though is occasionally an employee of lesser experience will execute a couple of queries to bog the system down. As a DBA I need awareness of the clumsier executions without constantly dropping everything to review each and every medium-grade RedGate monitor alert.  The halfway elegant solution I came up with looks like this:
DECLARE @sess varchar(7)
DECLARE @emMsg varchar(270)
DECLARE @sqlRun varchar(200)

set @sess = NULL

select TOP(1) @sess = ql.session_id, @sqlRun = ql.query_text from
select r.session_id
   (case when r.statement_end_offset = -1
   then len(convert(nvarchar(max), qt.text)) * 2
   else r.statement_end_offset end - r.statement_start_offset)/2)
   as query_text, r.cpu_time, r.total_elapsed_time
   , r.reads, r.logical_reads
 from sys.dm_exec_requests as r
 cross apply sys.dm_exec_sql_text(sql_handle) as qt
 inner join sys.dm_exec_sessions as es on r.session_id = es.session_id
 where es.is_user_process = 1
 ) as ql
 where ql.query_text not like '%where%'
 and ql.query_text not like '%top%'
 and ql.logical_reads > 200000

 IF @sess is not null


 set @emMsg = 'Session id ' + @sess + ' Running ' + @sqlRun

 EXEC msdb.dbo.sp_send_dbmail
    @recipients = 'jdchapman@mycompany.com',
    @subject = 'Unbounded Query Alert',
    @body = @emMsg
I created a SQL Server Agent job that runs this every ten minutes. This sends me an eMail when something is spinning up a lot of read activity, but it also filters out queries to just those missing a Where clause or a Top restriction.

It's not perfect enough that I might automatically kill SPIDs; sometimes it sends along an eMail from a long-running production job -- actually a good thing, as it alerts me to places I might have to trace or optimize later. It does tend to help me keep the SQL instance generally out of trouble though.

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