SQL Meditation

A forum for sharing what I have learned about SQL Server over many years of thought, contemplation and practice

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  • Blog Post: How to create a Deadlocked Scheduler Scenario at will

    First, please do not try this on your production server, because it will actually work. Second, this example is to illustrate how Deadlock scheduler issues can and do occur with the goal of increasing your understanding of the problem. Over the years of working with SQL Server, I learned that to understand...
  • Blog Post: Meditation: Replicate Data from Multiple Instances into a Single Reporting Database

    Somebody approached me recently with a question like this: Question : We’ll be hosting our existing application in one data center, but we’ll be setting up 2 more instances in two different data centers. Is possible to use replication to move all the data into an single database so that...
  • Blog Post: Choosing what SQLIO tests to Run and Automating the Tests

    Many companies rely on IO stress-testing tools like SQLIO Disk Subsystem Benchmark Tool (aka SQLIO) to perform an I/O subsystem validation before they deploy SQL Server in production. Over the years, I have seen a variety of SQLIO tests being used and many of them are not really necessary because they...
  • Blog Post: Meditation: The Tao of the Deadlock Scheduler in SQL Server

    Just thought I would summarize the concept of a SOS Scheduler and a Deadlocked Scheduler since many have inquired over the years for a brief summary of these concepts UMS/SOS Scheduler in SQL Server Since SQL Server 7.0, SQL Server has used its own scheduling mechanism, called UMS (User-mode...
  • Blog Post: Tasks, Workers, Threads, Scheduler, Sessions, Connections, Requests – what does it all mean?

    With this meditation I attempt to explain what some of the more common concepts that get used with SQL Server thread management and scheduling are. Parable: There was an all-powerful, but humble and benign Master, whom the workers revered and humbly served. The master accepted requests from other...
  • Blog Post: Meditation: Is IOCP listener actually listening?

    What is the IOCP Listener? The IOCP listener is a dedicated system thread that accepts incoming connections to SQL Server. It is a SQL Network Interface (SNI)-layer thread that listens for TCP/IP sockets or Named Pipes traffic (VIA is going away but still in the code). When a connection comes in,...
  • Blog Post: Meditation on Locked Pages in Memory and User Rights

    A colleague had the following question not too long ago Question : Does SQL Server check for “OS permissions” such as Locked Pages In Memory (LPIM) and if so does it use the Windows “macro-style” constants for them – such as SE_VOLUME_MANAGE? The reason I ask is that I’m still wanting to determine “major...
  • Blog Post: SQL RPC vs. Windows RPC

    Question : “If one executes stored procedures using the RPC events mechanism (instead of Language events ), do any additional RPC ports need to be open (as is the case with SSIS )? Configuring the Windows Firewall to Allow SQL Server Access - http://msdn.microsoft.com/en-us/library/cc646023...
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