Duty Free!!

SQL Write-Ahead Overhead…

Lightweight Thread Pooling / Fibre Mode

One of the rare tweaks that one would do on a SQl Server when excessive Context switches are found on SQLservr.exe, is to apply the Fibre mode. In this Fibre mode there is a higher probability that SQl Server gets hung or some applications doesnt work as they are supposed to. These applications might not be fibre-safe. Infact, though  SQL Server runs in fibre-mode, at the OS level still the process called SQL Server executes in thread mode. It is just that internal to the process the thread is finely used as a set of fibres that are light weight, meaning – not heavy in terms of their possessions so the context switching between fibres doesnt eat much of the resources. 

An application thats using datastructures pertaining to a thread like Thread  Local Storage, shall not be called “fibre-safe” and are prone to errors in fibre mode. 

Ken Henderson’s blog on msdn gives an insight into this in particular detail. One can find it here.

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January 20, 2009 - Posted by | SQL Server

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