Exploring mutexes, the Oracle RDBMS retrial spinlocks

TL;DR

This paper investigates Oracle's KGX mutex retrial spinlocks, analyzing their operation, performance, and contention in high-concurrency environments, and develops a predictive model for tuning and optimization.

Contribution

It introduces a detailed analysis of Oracle's KGX mutex spinlocks, including a mathematical model and experimental results for performance tuning.

Findings

Mutex contention increases with high concurrency

The mathematical model predicts mutex behavior accurately

Tuning parameters can reduce contention and improve performance

Abstract

Spinlocks are widely used in database engines for processes synchronization. KGX mutexes is new retrial spinlocks appeared in contemporary Oracle versions for submicrosecond synchronization. The mutex contention is frequently observed in highly concurrent OLTP environments. This work explores how Oracle mutexes operate, spin, and sleep. It develops predictive mathematical model and discusses parameters and statistics related to mutex performance tuning, as well as results of contention experiments.