Artifact Description [6ceb42809e]

Artifact 6ceb42809ed074d15af7fd6d044104b341794a53ab0c08c5ea93af3af671cdaf:

• File src/logstore_benchmark.zig
  • 2026-07-31 19:23:48 — part of check-in [e56a663b7a] on branch logstore-open-cost — bench: measure openReadOnly, not just open

    benchOpen timed LogStore.open -- the append path. Production never takes it: Repository.open falls back to openReadOnly, and Repository.logStore, the lazy content channel behind blob, cat, checkout and sync, calls openReadOnly with no cache in front. Every open number this effort has produced described a path no CLI verb enters.

    That was survivable while the two paths ran the same scan. It stops being survivable the moment either one scans header-only, at which point the bench would report the optimized path while production still paid the full cost. --mode append|read-only defaults to append so existing invocations report unchanged numbers, and the mode is in the output line because the two are only comparable when a captured log can tell them apart.

    Calibration on this tree, before any scan change: the modes agree within noise on all four shapes -- run B is 1% apart. That agreement is the check that the flag measures what it claims. (user: dmestas, size: 25159) [annotate] [blame] [check-ins using]

  • 2026-07-31 20:54:53 — part of check-in [90bd1b8015] on branch trunk — merge logstore-open-cost: header-only open scan and the verify verb

    Opening a repository checksummed every payload byte, so open cost scaled with the whole store rather than with what the caller asked for. The append path now scans header-only:

    10k frames 42 MB 42.2ms -> 11.2ms 10k frames 410 MB 298.0ms -> 12.7ms 100k frames 416 MB 511.9ms -> 119.2ms 100 frames 419 MB 321.4ms -> 0.10ms

    openReadOnly -- the path every CLI verb reaches -- deliberately still verifies payloads. Nothing has moved on the production path yet. That is Slice 2, and it is gated on this merge's other half: zit verify, the on-demand fsck that has to exist before eager detection is removed.

    The 100k-frame run settles a question the plan left open. Slice 4's gate was 'build the sidecar index only if that shape exceeds 150ms after the scan change'; it lands at 119ms. The sidecar is dead, and mmap with it -- separately, a mapping would keep shunned bytes resident and readable until every mapping dropped, which defeats the reclamation guarantee rather than merely slowing it. Both should be recorded as evaluated-and-rejected at the logstore extension comment; that is not done here.

    Also adds --mode append|read-only to the open benchmark. Every open number this effort had produced measured LogStore.open, which no CLI verb enters; the two modes agreed within noise before the scan change, which is what makes the after numbers above a comparison rather than two guesses.

    Verified on the merged tree: fmt clean, test 2327/2327. gate 19/19 and e2e 671/671 were watched green at the branch tip, which is content-identical -- trunk did not move between the branch point and this merge. (user: dmestas, size: 25159) [annotate] [blame] [check-ins using]