Benchmarking F# Data Structures — Introduction


DS_Benchmark is a new open source project for benchmarking F# data structures. I developed it to provide a platform for comparing performance across data structures, data types, common actions on structures, as well as scale-up performance. It currently supports almost all the structures in the FSharp Collections, FSharpX Data Structures, and Power Pack libraries. The project’s architecture allows incorporating additional structures and functions to be timed with minimal effort.

The choice of data structure in a functional language project profoundly influences architecture and performance. You may not have the time or inclination to read-up on purely functional data structures, and even if you are familiar with a lot of data structures and time complexity how do you choose between several choices all offering O(1) complexity in a crucial function, for instance? You should always do your own profiling, and especially profile performance critical code.

Some of the benchmarks possible with this project include:

Compare similar functions across data structures.

Investigate initializing structures from different collection types.

Look for pathologies caused by certain initial data.

At what scale does a data structure become less or more performant compared to other choices?


I intend the project to measure what I call “most common best case performance” in an “apples to apples” manner, so it does not readily tell you how many milliseconds a process took (although you can retrieve this information by not drilling down very deep in the project). I took the precautions I could think of to best isolate the event being measured. The project forces garbage collection prior to the event, and the timed event executes in it’s own exe. (It’s still important to minimize all other activity on the machine during timings.)

I found through experiment that less than 15% of timing executions are typically outliers on the long side, so DS_Benchmark times 100 executions and uses the fastest 85 to calculate a median time (in ticks) and the deviation from the median.

The output format is designed to enable further analysis within and across data structures by computing comparisons in terms of ratios (percents) rather than simply reporting milliseconds (which only apply to the host environment). Ratio comparisons are remarkably environment agnostic, as long as all original measurements are taken in the same environment. For instance I ran analyses based on measurements on two different machines, and even though the measured timings (in ticks) were wildly different, all of the comparative ratios I have analysed so far are very similar.

Simple Measurement Set-up

The console1 program in the solution provides documented examples of the most useful cases. Timings of individual scenarios print to the console, or you can generate batches of timings with a simple template model. The batched timings output to a tab-delimited file for easy import to Excel. (My next phase for this project is to persist the timing results and automate the analysis. The idea is to compare actions and inputs within and across data structures.)

For more in depth usage and architecture information see the project readme file.

Coming up Next

In following articles I will report on some interesting comparisons of data structures using DS_Benchmark. I am devoting a permanent section of this blog to F# Data Structures. Keep an eye on this space for benchmark comparisons as well as a single point of reference for many data structures and documentation, including time complexities, that otherwise are scattered all over the internet.

If you are interested in adding structures or otherwise contributing to the project, get in touch with me.

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