Designing Succinct Secondary Indexing Mechanism by Exploiting Column Correlations (Extended Version)

TL;DR

This paper introduces HERMIT, a novel succinct secondary indexing mechanism that exploits column correlations using a machine learning-enhanced data structure, significantly reducing space while maintaining query performance in RDBMSs.

Contribution

HERMIT leverages hidden column correlations and a new ML-based data structure to create space-efficient secondary indexes with minimal performance impact.

Findings

HERMIT reduces index space consumption significantly.

HERMIT maintains comparable query response times.

HERMIT performs well with complex range queries.

Abstract

Database administrators construct secondary indexes on data tables to accelerate query processing in relational database management systems (RDBMSs). These indexes are built on top of the most frequently queried columns according to the data statistics. Unfortunately, maintaining multiple secondary indexes in the same database can be extremely space consuming, causing significant performance degradation due to the potential exhaustion of memory space. In this paper, we demonstrate that there exist many opportunities to exploit column correlations for accelerating data access. We propose HERMIT, a succinct secondary indexing mechanism for modern RDBMSs. HERMIT judiciously leverages the rich soft functional dependencies hidden among columns to prune out redundant structures for indexed key access. Instead of building a complete index that stores every single entry in the key columns, HERMIT navigates any incoming key access queries to an existing index built on the correlated columns. This is achieved through the Tiered Regression Search Tree (TRS-Tree), a succinct, ML-enhanced data structure that performs fast curve fitting to adaptively and dynamically capture both column correlations and outliers. Our extensive experimental study in two different RDBMSs have confirmed that HERMIT can significantly reduce space consumption with limited performance overhead in terms of query response time and index maintenance time, especially when supporting complex range queries.