Database connection pooling with multi-threaded service

Question

I have a .NET 4 C# service that is using the TPL libraries for threading. We recently switched it to also use connection pooling, since one connection was becoming a bottle

Answer 1

You could look to control the degree of parallelism by using the Parallel.ForEach() method as follows:

var items = ; // your collection of work items
var parallelOptions = new ParallelOptions { MaxDegreeOfParallelism = 100 };
Parallel.ForEach(items, parallelOptions, ProcessItem)

In this case I chose to set the degree to 100, but you can choose a value that makes sense for your current connection pool implementation.

This solution of course assumes that you have a collection of work items up front. If, however, you're creating new Tasks through some external mechanism such as incoming web requests the exception is actually a good thing. At that point I would suggest that you make use of concurrent Queue data structure where you can place the work items and pop them off as worker threads become available.