fix(compute/build): normalise and bucket heap allocations #1130
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Integralist
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cee-dub
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Feb 14, 2024
Co-authored-by: Cameron Walters (cee-dub) <cameron.walters@gmail.com>
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Thanks @cee-dub 👍🏻 |
jdno
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The collection of metadata was disabled in rust-lang#387, because the metadata contained an unstable property that broke the change detection in Terraform. This issue has been resolved upstream by introducing buckets for the heap allocation size, which reduces the risk of changes in the metadata while preserving the usefulness of the property. See fastly/cli#1130 for details on the buckets.
jdno
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The collection of metadata was disabled in rust-lang#387, because the metadata contained an unstable property that broke the change detection in Terraform. This issue has been resolved upstream by introducing buckets for the heap allocation size, which reduces the risk of changes in the metadata while preserving the usefulness of the property. See fastly/cli#1130 for details on the buckets.
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Problem
We started annotating Wasm binaries with additional metadata and part of that data was the number of memory heap allocations. Including this metric means every time you build a package (even if you have changed ZERO lines of code) it'll produce a package with a different hash (e.g.
fastly compute hash-files). This behaviour breaks Terraform's ability to reason about whether the package has changed, as each time you build the amount of memory used to create the package is variable/fluctuating.Solution
We're going to bucket the memory allocation numbers to provide a consistent output. If the memory allocations increase significantly then the bucket value will change (as we're considering the change significant enough to be considered some kind of important code/dependency change).
Screenshots
Below demonstrates me building a package twice (no code changes) and the memory allocation value is now consistent (
2-5MB):The following demonstrates me building a package twice (no code changes) and the hash produced is thus the same: