census: never_read age bands (bucketed by created age) - #48
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A never-read entry evicted minutes after writing means the cache could not hold a write until its first read - the worst eviction outcome. It was counted only in the aggregate never-read counter (no age dimension) and the created bands (mixed with read entries), so a young never-read eviction rendered as a healthy-looking last_read mix. New age_kind=never_read series on evicted_bytes_by_age, bucketed by created age. created stays the superset; last_read stays the pure live-harm signal. Co-authored-by: Cursor <cursoragent@cursor.com>
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Not needed: the dashboard now composes the staleness histogram from the existing last_read bands + never-read counter, with never-read as a single band (we decided the created-age of never-read evictions isn't a stat we care about). |
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A never-read entry evicted minutes after creation is the cache failing to hold a write until its first read — the worst eviction outcome — but it was invisible as such: the never-read counter has no age dimension, and the created bands mix never-read with previously-read bytes.
This adds
age_kind=never_readtobazel_remote_disk_cache_evicted_bytes_by_age, bucketed by created age.createdremains the superset of every eviction;last_readremains the pure live-harm signal. Census JSONL rows are unchanged (they already carryevicted_never_read_bytesper tenant).Feeds the young-eviction panels on the Bazel L1 Grafana board (fa#5699); until this rides a release+roll, the board approximates via the created bands.
Tested: census accounting test now asserts the 24h never_read band after a young never-read eviction;
go test ./cache/disk/green.Made with Cursor
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