This repository contains an implementation of the approximate k-Nearest Neighbors (ANN) algorithm using multiple parallelization techniques: Sequential, OpenMP, OpenCilk, and Pthreads

The project implements the k-Nearest Neighbors (k-NN) algorithm, which finds the closest data points to a given query point. This project aims to improve the k-NN algorithm's performance using parallelization strategies to handle large datasets efficiently. The project uses the ANN (Approximate k-NN) approach for faster processing at the cost of a small loss in accuracy (recall).

Before running the script, ensure that you have the following installed:

• make: For building the project.
• OpenMP: Install the OpenMP library for multi-threaded execution.
• OpenCilk: Install the OpenCilk runtime for parallel execution.
• Pthreads: Ensure that the Pthreads library is available for thread-based parallelization.
• OpenBLAS: For fast linear algebra computations, used in distance calculation.
• Linux/Unix environment: For running the bash scripts and performance tools.

To compile and execute different implementations on specified datasets, follow these steps.

Script location:

The script used for running benchmarks and experiments is located at:

 `./Results/run.bash`

• Note: Before running parallel implementations for a dataset, you must first execute the Sequential implementation (need the results for recall and speedup calculations)

bash run_script.sh <type> <dataset> <sampling_reduction> <candidate_reduction> [MIN_SIZE_factor] [THREADS_NUM]

• <type>: The implementation type (Sequential, OpenMP, OpenCilk, Pthreads).

• <dataset>: The dataset to run the program on (mnist, fashion-mnist, sift).

• <sampling_reduction>: The sampling reduction factor (positive integer).

• <candidate_reduction>: The candidate reduction factor (positive integer).

• [MIN_SIZE_factor] (optional): To divide MIN_SIZE (default is 1).

• [THREADS_NUM] (optional): The number of threads to use (default is 1).

  • Note: For Pthreads, the number of threads must be manually specified in the code by changing the MAX_THREADS define in ./src/knn_Pthreads.c.

1. Run Sequential Implementation:

   bash run.bash Sequential mnist

2. Run OpenCilk Implementation with 12 threads:

   This command will run the OpenCilk implementation on the mnist dataset with a sampling reduction of 25, candidate reduction of 200, and a minimum size factor of 1. It will use 12 threads.

   bash run.bash OpenCilk mnist 25 200 1 12

After the script has completed running, the results will be saved in the following directory structure:

• Analytic Results:

  • Location: ./<type>/<dataset>/Analytic/results_<dataset>_<sampling_reduction>_<candidate_reduction>_<minsize_factor>.txt
  • Contains indices of k nearest neighbors for each query.

• Statistics

  • Location: ./<type>/<dataset>/Statistics/statistics_<dataset>_<sampling_reduction>_<candidate_reduction>_<minsize_factor>.txt
  • Summarizes performance metrics, including execution time, recall, and queries per second.

The directory structure will be created if it does not already exist.