Confluent Persistence Revisited

TL;DR

This paper presents a method to efficiently make any pointer-based data structure confluently persistent with logarithmic time for updates and queries, significantly improving over previous approaches.

Contribution

It introduces a new technique to achieve confluent persistence with logarithmic overhead, improving the space and time efficiency of persistent data structures.

Findings

Updates in $O(\log n)$ amortized time

Pointer following in $O(\log c \log n)$ time

Logarithmic cost in the bounded in-degree model

Abstract

It is shown how to enhance any data structure in the pointer model to make it confluently persistent, with efficient query and update times and limited space overhead. Updates are performed in $O(\log n)$ amortized time, and following a pointer takes $O(\log c \log n)$ time where $c$ is the in-degree of a node in the data structure. In particular, this proves that confluent persistence can be achieved at a logarithmic cost in the bounded in-degree model used widely in previous work. This is a $O(n/\log n)$-factor improvement over the previous known transform to make a data structure confluently persistent.