Lightning Talk – Test Result Caching at Dropbox
summary
Dropbox migrates rules to Bazel, fixes nonreproducible outputs (caught a Rust nightly bug), and uses the build event stream to show 10–20% reduction in tests run by fetching passing test results from a multi-layer HTTP remote cache (planning gRPC). Tests cache only when passing; Docker tests remain uncached because they touch the Docker daemon. Cache eviction uses a 90-day TTL to S3, a root key flip clears poisoned cache, and flaky tests trigger 10 reruns with caching disabled.
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