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Tailscale confirms deeply buried 16-year-old SQLite flaw caused last year's outages
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Users of peer-to-peer networking outfit Tailscale might have struggled through some surprising outages beginning late last year.
Key facts
- SQLite has an option to improve performance and concurrency known as the Write-Ahead Log (WAL), which serves as the aforementioned hopper
- We’ve used SQLite as our primary database since 2022, and we chose it because it's well-known, reliable, and widely used,” Chan wrote in the company’s post-mortem
- In our current backup pipeline, we take a complete snapshot of the database every few minutes, then upload the entire SQLite file to an S3 bucket,” Chan said, but in August 2025 those backups began
- The Tailscale team couldn’t reproduce the issue because there were no reliable triggers for it
Summary
The Tailscale team announced in a Wednesday blog post that it had finally addressed the issue with the help of SQLite maintainers, who even had to create a new tool (with Tailscale funding) to log virtual file system activity to track the thing down, which Tailscale software engineer Alex Chan described as resisting “all our initial attempts to find it.” According to Chan, the problem goes deep into the nature of SQLite, so deep that the database maintainers had to add code to reproduce it. To understand what happened, it’s necessary to know how Tailscale works. “We’ve used SQLite as our primary database since 2022, and we chose it because it's well-known, reliable, and widely used,” Chan wrote in the company’s post-mortem.