feat(git): instrument background prewarm with metrics#315
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Adds three metrics for the prewarm-most-cloned-repos background pass:
- cachew.git.prewarm_repo_duration_seconds (histogram, labelled path=fetch|restore, status=success|error)
- cachew.git.prewarm_pass_duration_seconds (histogram, labelled outcome=complete|empty_histogram)
- cachew.git.prewarm_passes_total (counter, labelled outcome)
These let us see whether prewarm is actually paying off — pair with cachew.git.snapshot_serves_total{source=...} to validate that warm repos correlate with cache-hit serve rates.
Amp-Thread-ID: https://ampcode.com/threads/T-019e4193-0c35-732e-96f0-b9c97aed2fae
Co-authored-by: Amp <amp@ampcode.com>
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Stacks on #299. Adds three metrics for the background prewarm pass:
cachew.git.prewarm_repo_duration_seconds(histogram): per-repo wall time, labelledpath(fetch= mirror already on disk,restore= mirror snapshot pull or full clone) andstatus(success|error).cachew.git.prewarm_pass_duration_seconds(histogram): total pass wall time, labelledoutcome(complete|empty_histogram).cachew.git.prewarm_passes_total(counter): pass completions byoutcome.Pair with
cachew.git.snapshot_serves_total{source=...}to validate that prewarmed repos correlate with cache-hit serve rates. If the data shows prewarm isn't moving the needle on first-request latency or upstream load, we have justification to drop the prewarm work entirely.