Run T-SQL in Parallel

Writing CLR procedures to run T-SQL concurrently is not an extremely new idea. I have seen a lot of implementations and I have written and improved it many times by myself as well. After those coding exercises, I found few important things were not (or just partially) addressed.

  • Termination of launcher session: Either the launcher session get cancelled or killed, running asynchronous workers should be cancelled.
  • Different ways to shut down a batch: Waiting Workers should be abandoned. Executing workers should be either cancelled or waited to be completed.
  • Effective monitoring: People want to see which session is running what.
  • Adjustable maximum threads in the course of execution.

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Print Long String

Quite often, I output information through PRINT command. It works well only when message is shorter than 8000 bytes. When the message is greater than 8000 bytes, extra-characters will be removed. the simplest way to overcome this is to make a loop and print 8000 characters at a time

declare @line nvarchar(max) = Replicate(cast('0123456789' as varchar(max)), 800)+'abc
select @line = replicate(@line, 3)
declare @pos int = 1
while @pos <= len(@line)
	print substring(@line, @pos, 8000)
	select @pos = @pos + 8000

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Inserted and Deleted are One Table?

Inserted and deleted tables are 2 pseudo tables preseting the before and after images of modified rows. They can only be accessed from within triggers. Those two have been around for quite long time but it’s hard to find any articles to tell how they are populated. Some rumors said they are retrieved from transaction logs in SQL Server 2000. Recently, I was asked to evaluate the performance impact of using trigger for my customer’s project. I did some investigation and got some interesting results.

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Microsoft Roslyn Rocks

Recently I was looking for a solution for dynamic code compiling. I came cross Microsoft Roslyn and had a test. It’s perfect solution for dynamic code compilation and execution. You will have to have .net 4.0, Visual Studio 2010 sp1, Visual Studio 2010 SDK sp1, and Microsoft Roslyn installed in order to make this happen.

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Implementing IDataReader

Last post, I talked about Customized Event and setting up trace for web applications which usually use pooled connection. Assuming you already have everything setup, SqlCommand component has been wrapped up to send an customized event with user or session information before an actually procedure call taking place. The trace is also setup to receive both procedure calls and customized events. To simplify the scenario, trace only capture the customized event and RPC Complete with column SPID, TextData, StartTime. To receive the trace data, you can either save them to the disk then read the trace file from the disk or directly stream the trace data.( see my post here for detail). After trace data being read, there will be always a customized event prior to an actual procedure call. When you are asked to get SQL Server response time for an particular application, for instance, give me average respose time of procedure ABC every 30 minutes during the day for that user, you can query the table includes the trace rows to locate all procedure ABC, then based on SPID and identity values to find previous record to get the user information of the procedure call, perform filter, aggregates…It will be fine if your table is small. The trace system generate more than 500MB data every hour, performing such query will be very challenging irrespective of how you design the indexes on the trace table. Now you may think to re-format the trace data to table with columns, EventID, SPID, TextData, StartTime, and UserInfo to simplify the query. But SQL Profiler cannot do it in that way, you will have to write an ETL for that.

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