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Category: Locks, Blocks, and Deadlocks

Concurrency Simulator

Published 2016-02-19 by Kevin Feasel

Michael J. Swart has come up with a concurrency simulator:

Capacity planning is difficult for DBAs who expect growth. Will there be enough CPU, Memory or I/O to serve the anticipated load? One category falls outside those three, logical contention.

Logical contention is a problem where excessive blocking causes throughput to suffer. It would be great to get advanced warning. One essential strategy is to make use of the blocked process report. The problem is that blocked process reports are an alarm metric, not a guage metric. In other words, the blocked process report can indicate when there is a problem, but it is poor at giving advanced notice.

This is a nice visual tool to begin to understand the topic.  The same principles apply to road traffic, water flow, etc.

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Capturing Blocking Information

Published 2016-01-04 by Kevin Feasel

Erin Stellato shows us how to capture details when processes are blocked:

To view the output from extended events you can open the .xel file in Management Studio or query the data using the sys.fn_xe_file_target_read_file function. I typically prefer the UI, but there’s currently no great way to copy the blocking report text and view it in the format you’re used to.  But if you use the function to read and parse the XML from the file, you can…

If you can’t buy a tool which monitors long-term blocking, you can still build it yourself pretty easily.

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Spinlocks

Published 2015-11-16 by Kevin Feasel

Ewald Cress investigates spinlocks:

SQL Server spinlocks are famously elusive little beasties, tending to stay in the shadows except when they come out to bother you in swarms. I’m not going to add to the documentation of where specific spinlock types show up, or how to respond to contention on different types; the interested reader likely already knows where to look. Hint: Chris Adkin is quite the spinlock exterminator of the day.

In preparation for Bob Ward’s PASS Summit session, I figured it would make sense to familiarise myself a bit more with spinlock internals, since I have in the past found it frustrating to try and get a grip on it. Fact is, these are actually simple structures that are easy to understand, and as usual, a few public symbols go a long way. Being undocumented stuff, the usual caveats apply that one should not get too attached to implementation details.

Spinlocks are a testament to the level of engineering complexity in the SQLOS model.  I appreciate Ewald’s explanation of the topic.

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