# ROOT I/O compression algorithms and their performance impact within Run 3

## TL;DR

This paper evaluates various data compression algorithms within the ROOT framework to optimize data handling for LHC Run 3, exploring new techniques to enhance performance and reduce resource usage.

## Contribution

It provides a comprehensive survey of new compression algorithms and techniques, including parallelism and pre-conditioners, to improve ROOT data processing performance.

## Key findings

- New algorithms can significantly reduce I/O and bandwidth usage.
- Parallelism and pre-conditioners improve compression speed and efficiency.
- Performance bottlenecks can be mitigated with optimized solutions.

## Abstract

The LHCs Run3 will push the envelope on data-intensive workflows and, since at the lowest level this data is managed using the ROOT software framework, preparations for managing this data are starting already. At the beginning of LHC Run 1, all ROOT data was compressed with the ZLIB algorithm; since then, ROOT has added support for additional algorithms such as LZMA and LZ4, each with unique strengths. This work must continue as industry introduces new techniques - ROOT can benefit saving disk space or reducing the I/O and bandwidth for online and offline needs of experiments by introducing better compression algorithms. In addition to alternate algorithms, we have been exploring alternate techniques to improve parallelism and apply pre-conditioners to the serialized data. We have performed a survey of the performance of the new compression techniques. Our survey includes various use cases of data compression of ROOT files provided by different LHC experiments. We also provide insight into solutions applied to resolve bottlenecks in compression algorithms, resulting in improved ROOT performance.