Parallelise skill file fetches and reuse HTTPS connections#5335
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LGTM. Focused change, the two halves (parallel fetches + shared transport with bumped MaxIdleConnsPerHost) belong together. Tests verify the right invariants (both goroutines reach the fetcher before either releases; errgroup propagates cancellation to in-flight peers) and survived -race -count=50 locally.
Nits, none blocking:
- The
8concurrency limit and* 2idle-conn slack would benefit from a one-line rationale. sync.OnceValueis the codebase's lazy-init idiom (e.g.libs/clicompat/clicompat.go); the IIFE works fine since init is eager, just flagging for consistency.- Skills are still installed serially across the outer loop, so the cold-start win mostly comes from the shared client keeping idle conns warm between skills, not intra-skill parallelism. Worth a sentence in the PR body.
TestInstallSkillToDirCancelsInFlightFetchesOnErroruses a 1s deadline; bumping to ~5s would be cheap CI insurance.
Each skill file was fetched sequentially with a fresh http.Client per call, so every file paid the full TCP+TLS handshake to raw.githubusercontent.com and `databricks aitools install --experimental` (26 skills, ~120 files) took ~40 s on a cold network. Hoist a shared http.Client with a tuned transport, and fetch a skill's files concurrently with errgroup. Wall-clock drops to under a second. Co-authored-by: Isaac
Cover concurrent skill file fetches and errgroup cancellation so the installer performance path keeps its intended behavior.
- Switch the test's `sync.Once` to `sync.OnceFunc` to satisfy the forbidigo lint rule (the cause of the CI lint failure). - Convert the package-level httpClient initialiser to `sync.OnceValue` for consistency with the codebase's lazy-init idiom (e.g. clicompat). - Add a one-line rationale for the fetchConcurrency value (8) and the MaxIdleConnsPerHost * 2 idle-conn slack. - Bump the cancellation test's outer deadline from 1s to 5s for CI slack. Co-authored-by: Isaac
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Summary
http.Clientinlibs/aitools/installer/installer.goso the transport pool reuses TCP+TLS connections across fetches.MaxIdleConnsPerHostis bumped from Go's default 2 → 16 so parallel fetches toraw.githubusercontent.comactually reuse connections instead of churning handshakes.installSkillToDirviaerrgroup.WithContextwithSetLimit(8). First error cancels in-flight peers, preserving the prior bail-on-first-error semantics.Why
databricks aitools installwas sequential: every file constructed a fresh&http.Client{}and threw it away, paying the full TCP+TLS handshake per file. For--experimental(26 skills × ~5 files each = ~120 HTTPS GETs to GitHub raw) that meant wall-clock was dominated by handshake round-trips.Benchmarked locally against
https://raw.githubusercontent.com/databricks/databricks-agent-skills/v0.2.0with a freshly built CLI on each side:The cold-start number is what a first-time
databricks aitools install --experimentaluser actually pays.The
fetchFileFnpackage var that tests stub remains unchanged, so no test mocks need updating.Test plan
go test ./libs/aitools/...— all green, including-race -count=2.gofmt -l libs/aitools/installer/installer.go— clean.go vet ./libs/aitools/...— clean.This pull request and its description were written by Isaac.