Vercel
Vercel Flags SDK now initialises 7x faster on cold starts and reports usage without keeping functions running after they return a response.
According to the Vercel changelog, p75 initialisation time fell from more than 70 ms to 10 ms in internal testing. Builders can get the changes by updating @flags-sdk/vercel to version 1.5.3 or later.
- Cold-start improvement
- 7x
- internal testing
- Previous p75
- Over 70 ms
- SDK initialisation
- New p75
- 10 ms
- SDK initialisation
- Required version
- 1.5.3 or later
- @flags-sdk/vercel
How Vercel Flags SDK cut cold-start time
Two changes remove work from the first flag evaluation.
The SDK now loads and parses the flags datafile bundled with a deployment when the client is created. This means the datafile is ready before application code evaluates its first flag.
Each function invocation also receives the current datafile revision. The SDK can compare that revision with its bundled datafile and check whether the data is current without making a network request.
Previously, that network wait contributed to cold-start latency. Removing it reduced the measured p75 from more than 70 ms to 10 ms.
This applies when a function starts cold. The improvement reduces the time spent preparing feature flag data before the function can evaluate a flag and continue handling the request.
Usage reporting stops extending function duration
The same SDK update changes how usage events leave the function. Usage reporting previously used waitUntil, which kept the function running after it had returned its response.
Events are now passed to the Vercel runtime instead. Usage reporting can continue without adding to the function’s duration after the response has been sent.
The change addresses two separate sources of function time: the network wait during cold-start initialisation and the reporting work after a response. Both changes are included in version 1.5.3 or later of the package.
Frequently asked questions
What is Vercel Flags SDK? Vercel Flags SDK evaluates feature flags inside applications deployed on Vercel. It uses a flags datafile bundled with the deployment and reports flag usage through the Vercel runtime.
How much faster is Vercel Flags SDK? Vercel measured a 7x improvement in internal cold-start testing. P75 initialisation time fell from more than 70 ms to 10 ms.
Which Vercel Flags SDK version includes these changes?
The faster initialisation and revised usage reporting are available in @flags-sdk/vercel version 1.5.3 or later. The changelog does not list pricing or plan requirements.
Sources
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