Vitess Engineering Team | March 8, 2024

We're thrilled to announce the release of Vitess 19, the latest version packed with enhancements aimed at improving the scalability, performance, and usability of your database systems. With this release, the Vitess team continues our commitment to providing a powerful, scalable, and reliable database clustering solution for MySQL.

What's new in Vitess 19

• Dropping Support for MySQL 5.7: As Oracle marked MySQL 5.7 end of life in October 2023, we're also moving forward by dropping support for MySQL 5.7. We advise users to upgrade to MySQL 8.0 while on Vitess 18 before making the jump to Vitess 19. However, Vitess 19 will still support importing from MySQL 5.7.
• Deprecations: We're cleaning house to streamline our offerings and improve maintainability. This includes deprecating several VTTablet flags, MySQL-specific tags of the Docker image vitess/lite, and changes to the EXPLAIN statement format.
• Breaking Changes: Notably, ExecuteFetchAsDBA now rejects multi-statement SQL, enforcing stricter security and stability practices.
• New Metrics: We're introducing new metrics for stream consolidations and adding the build version to /debug/vars to provide deeper insights and traceability.
• Enhanced Query Compatibility: This release brings support for multi-table delete operations, a new SHOW VSCHEMA KEYSPACES query, and several other SQL syntax enhancements that broaden Vitess's compatibility with MySQL.
• Apply VSchema Enhancements: We've added a --strict sub-flag and corresponding gRPC field to the ApplyVSchema command, ensuring that only known parameters are used in Vindexes, enhancing error checking and config validation.
• Tablet Throttler: Throttlers now communicate via gRPC only. HTTP communication is no longer used. This closes a possible vulnerability vector.
• Online DDL: Support for backoff for cut-over attempts in the face of locking. Support for forced cut-over.
• Incremental Backup: Support for backup names and empty backups.
• Table lifecycle: Quicker cleanup flow.
• Performance improvements: Including a new connection pool for the Tablets, faster hashing in sharded Vitess clusters, and faster aggregations in the Gates.

New and updated features

Let's take a closer look at some of the key features.

Query compatibility enhancements

Vitess 19 introduces several SQL syntax improvements and compatibility features, including:

• Support for AVG() aggregation function on sharded keyspaces, utilizing a combination of SUM and COUNT.
• Non-recursive Common Table Expressions (CTEs) support, allowing for more complex query constructions.

Tablet throttler

Inter-throttler communication is now solely based on gRPC. HTTP communication is no longer supported.

Online DDL

Vitess migration cut-over now uses back-off in the face of table locks. If unable to cut-over, subsequent attempts take place at increasing intervals. This reduces the impact on an already overloaded production system.

Online DDL also supports forced cut-over, at either predetermined timeout or on demand. Forced cut-over prioritizes the completion of cut-over operations over production traffic and terminates queries and transactions that conflict with the cut-over.

See this PR for more information.

Incremental backup

The flag Backup|BackupShard –incremental-from-pos now accepts a backup name as the backup starting point.

An empty incremental backup is now allowed, and the Backup|BackupShard command returns with a success error code, even though no backup manifest or other artifacts are created.

Table lifecycle

The table GC mechanism is now more responsive to tables that need to be garbage collected and can observe operations that generate GC tables. For example, it can capture the result of an ALTER VITESS_MIGRATION … CLEANUP command and move the table through the relevant stages within seconds rather than taking several minutes or hours.

Breaking change: ExecuteFetchAsDBA

The command ExecuteFetchAsDBA now rejects multi-statement input. Previously, multi-statement input was implicitly allowed but resulted in undefined and undesired behavior: errors were only reported for the first statement and silently dropped for successive statements. The connection was left in an undefined state and could leak results to subsequent users of the connection pool. The schema tracker would not be notified of changes until the connection was closed. We will introduce formal multi-statement support in a future version.

Performance improvements

Following the trend over the past 3 years, this new Vitess release is faster than the previous one in all the benchmarks we track in Arewefastyet. We've fixed several performance regressions from Vitess 18 and introduced significant performance improvements.

New connection pool

The connection pool for MySQL connections in the Tablets has been rewritten from scratch. The new pool is architected over several lock-free stacks and provides significantly lower query latencies, lower and more fair wait times, and more efficient usage of idle connections. This is particularly noticeable in Vitess clusters with external tablets (i.e., clusters where the Tablet and the MySQL instance are deployed on different hosts) and busy Vitess clusters with many point queries.

Faster hashing in sharded Vitess clusters

The VIndex hasher for textual columns was previously implemented using the x/text/collate package, which allocates a linear amount of memory based on the length of the column being hashed. We've replaced it with a custom, backwards-compatible implementation that is both faster and uses a constant amount of memory. This is a very significant performance improvement for sharded tables that use large textual columns as sharding keys.

Faster comparisons in cross-shard aggregations

The performance of cross-shard aggregations that use ORDER or GROUP BY qualifiers has been greatly improved by introducing Tiny Weights. The query executor in the VTGates now tags all the SQL values from the upstream shards with a compressed form of their weight string, allowing constant-time comparisons while performing aggregations.

We're excited to see how you'll use Vitess 19 to scale your database systems. As always, we're eager to hear your feedback and experiences. Join us on our GitHub or Slack channel to share your stories, ask questions, and connect with the Vitess community.

Getting started

Upgrading to Vitess 19 is straightforward, but we recommend reviewing the detailed release notes for a smooth transition. Check out our documentation for comprehensive guides and tips.

Thank you for your continued support and contributions to the Vitess project. Here's to making database scaling even easier and more efficient with Vitess 19!

The Vitess Team