author: Marten Voorberg
title: There Can Be Only (the Fastest) One
keywords: algorithms and data structures, performance testing
topics: Algorithms and Data Structures , Case studies and Applications
committee: Vadim Zaytsev
started: April 2021


There are many data structures known to humankind, some more popular than others. It can be said that each data structure has two sides: the external side with visible commitments (like a list that promises to keep the order in which the elements are stored and retrieved, but a set does not save the order but promises each element uniqueness instead), and the internal side with the implementation details (something behaving like a set can be implemented based on an array, a list, a bit map, etc). For example, if we focus on the external side of collections, we can think of at least the following ones:

  order matters order does not matter
duplicate elements allowed list, array bag, multiset, counter
all elements unique uniq set, hashset
key-value mapping sorted dictionary map, hashmap, dictionary

(with "uniq" we denote the unnamed data structure that the Linux tool uniq, which prints input lines in order but skips duplicate ones)

Focusing on structures meant for active adding and removing elements, this can be done LIFO or FIFO, which adds two more: a stack or a queue/channel.

Each of these basic eight data structures supports its own range of operations which makes sense for it: for instance, a stack should support at least push and pop, but a reasomable implementation should show good performance also for peek, drop, dup and rot.

The idea behind this project is to do the following:

  • For each of these 8 data types,
    • identify the main set of operations expected to be supported (mostly by reading books on algorithms and data structures)
    • find the corresponding data types in some popular portable framework (such as JVM or .NET Core), reimplement those
    • find state of the art implementation variants that did not make it yet to the mainstream platforms, implement those
    • find state of the art benchmarks used to compare data structure implementations in practice
  • That's it. Visualise results, and give advice in which cases which implementation is the most practical (i.e., efficient for all operations, some operations, having the best performance-effort ratio, etc).

NB: There is a strong preference for using a platform not necessarily geared towards performance (such as .NET Core or JVM) instead of, say, bare C/C++, because (1) implementations of complex data structures are considerably harder in a low-level non-garbage-collected language and (2) most such questions have already been answered with concrete libraries. This project aims more at answering a mainstream developer's questions like "is using Stack<...> enough, or do I need to code up my own linked list implementation for my program to be fast?"

Membership data structures support one query: determining whether a certain element is contained in the data structure.

Much research has gone into such data structures with very good theoretical space and time complexity, but these data structures are often to complicated to implement in practise. This research will evaluate the performance of different kinds of member data structures which can realistically be implemented, on simulated real-world data distributed in a variety of ways. Additionally the research will examine the potential for performance gains by switching to a probabilistic membership data structure, such as Bloom filters.