We are excited to announce that Vitess now supports recursive Common Table Expressions (CTEs), marking another significant step in our journey to fully align with MySQL’s capabilities. Recursive CTEs, often a critical feature for complex query handling, allow for the execution of recursive queries within a single CTE. This addition brings more flexibility and power to developers using Vitess, especially those working with distributed databases. One of the key challenges in implementing recursive CTEs within a sharded environment is managing the distribution of data across multiple shards.

Vitess is a popular CNCF project that is used to scale some of the largest MySQL installations in the world — by companies like Slack, Square, Shopify, and GitHub. It provides sharding, connection pooling, and many other features that make it easy to scale MySQL horizontally. Vitess and MySQL are ideally suited for use as an Online Transaction Processing (OLTP) system — where the end-user interacts directly with the system and fast response times are essential as they get product and service information, generating critical business records such as orders, user profiles, and more.

Introduction # I recently encountered an intriguing bug. A user reported that their query was causing vtgate to fetch a large amount of data, sometimes resulting in an Out Of Memory (OOM) error. For a deeper understanding of grouping and aggregations on Vitess, I recommend reading this prior blog post. The Query # The problematic query was: selectsum(user.type)fromuserjoinuser_extraonuser.team_id=user_extra.idgroupbyuser_extra.idorderbyuser_extra.id;The planner was unable to delegate aggregation to MySQL, leading to the fetching of a significant amount of data for aggregation.

Vindex # Vitess uses Vindexes (short for Vitess Index) to associate rows in a table with a designated address known as Keyspace ID. This allows Vitess to direct a row to its intended destination, typically a shard within the cluster. Vindexes play a dual role: enabling data sharding through Primary Vindexes and facilitating global indexing via Secondary Vindexes. Through this mechanism, Vindexes serve as an indispensable tool for routing queries in a sharded database, ensuring optimal performance and scalability.

My name is Arvind Murty, and from May to July of 2023, I worked on Vitess via an internship with PlanetScale. I was first introduced to Vitess when I was in high school as a potential open-source project for me to work on. I had been interested in working on one because they’re a relatively easy way to get some real-world experience in large-scale software development. Vitess seemed like an good place to start, so I started contributing, mostly on internal cleanup.

Serverless databases are a modern approach to database technology. Unlike traditional databases, where users have to manage server infrastructure and capacity planning, serverless databases remove those complexities. Users can focus solely on their data and applications, leaving the database infrastructure provisioning, scaling, and maintenance to the service provider.

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