Online Schema Evolution is (Almost) Free for Snapshot Databases

TL;DR

Tesseract enables online, transactional schema evolution in snapshot databases with minimal overhead by modeling schema changes as data modifications, avoiding downtime and maintaining high performance.

Contribution

The paper introduces Tesseract, a novel approach that leverages data modification operations to support online schema evolution without service interruption.

Findings

Supports schema changes with negligible performance impact

Operates without downtime across various workloads

Works efficiently on a 40-core server

Abstract

Modern database applications often change their schemas to keep up with the changing requirements. However, support for online and transactional schema evolution remains challenging in existing database systems. Specifically, prior work often takes ad hoc approaches to schema evolution with 'patches' applied to existing systems, leading to many corner cases and often incomplete functionality. Applications therefore often have to carefully schedule downtimes for schema changes, sacrificing availability. This paper presents Tesseract, a new approach to online and transactional schema evolution without the aforementioned drawbacks. We design Tesseract based on a key observation: in widely used multi-versioned database systems, schema evolution can be modeled as data modification operations that change the entire table, i.e., data-definition-as-modification (DDaM). This allows us to support schema almost 'for free' by leveraging the concurrency control protocol. By simple tweaks to existing snapshot isolation protocols, on a 40-core server we show that under a variety of workloads, Tesseract is able to provide online, transactional schema evolution without service downtime, and retain high application performance when schema evolution is in progress.