fix(localdb): snapshot as_of_seq floors at last_acked_seq so a rebuilt peer's watermark is lifted — ends the full-snapshot-on-every-reconnect loop (0.3.4, ScadaBridge register row 106)

SnapshotStreamer.SendAsync stamped as_of_seq = MAX(seq), which reads 0 once ack-pruning has
emptied a converged sender's oplog. A receiver whose watermark genuinely is 0 (a rebuilt node —
ScadaBridge's site-a-a since its 2026-08-15 rebuild) was healed by the snapshot but never lifted
by it (the receiver's watermark update is correctly MAX-guarded), so the 0.1.2 empty-oplog
horizon rule saw 0 < last_acked_seq as a gap on every subsequent handshake and re-streamed the
whole database on every reconnect until the sender wrote again. Observed live: the same 127k-row
full snapshot on two consecutive restarts of the pair.

Fix: as_of_seq = max(MAX(seq), last_acked_seq). Every delta pruned below last_acked_seq is
already folded into the rows the snapshot carries, so that is the floor it may claim; the
receiver's MAX guard then lifts the watermark and the next handshake finds no gap. Sender-side
only; wire-compatible; no schema change.

Test WipedPeer_SnapshotLiftsItsWatermark_SoTheNextReconnectSendsNoSecondSnapshot fails on the
unfixed code exactly as the rig does (watermark 0, expected 3) and passes with the fix: the
second episode exchanges only a delta, and a capturing logger on the snapshot streamer proves
no snapshot was sent. Suite 216/216 on 8 of 9 runs; one unnamed single-test failure on the first
run did not recur in eight further runs and could not be attributed.
This commit is contained in:
Joseph Doherty
2026-08-20 09:52:19 -04:00
parent 5e02c1c38f
commit 75c1897522
4 changed files with 93 additions and 5 deletions
+1 -1
View File
@@ -5,7 +5,7 @@
<Nullable>enable</Nullable>
<ImplicitUsings>enable</ImplicitUsings>
<LangVersion>latest</LangVersion>
<Version>0.3.3</Version>
<Version>0.3.4</Version>
<ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally>
<TreatWarningsAsErrors>true</TreatWarningsAsErrors>
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