fix(likes): count unique visitors and sync denormalized counter#96
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fix(likes): count unique visitors and sync denormalized counter#96cursor[bot] wants to merge 1 commit into
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Parallel setLike races could leave multiple likes rows for one ipHash. Reads used row count (and backfill incremented per row), inflating counts. Dedup decrements could also desync the denormalized counter. Count distinct ipHashes, sync the counter after each mutation, and rebuild backfill totals per URL from unique visitors. Co-authored-by: Injoon Oh <injoon5@icloud.com>
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Bug and impact
Recent denormalized like counts (PR #85) could show inflated or deflated totals when parallel
setLikecalls left duplicatelikesrows for the same visitor, or when dedup deleted extra rows while decrementing a counter that never reflected those rows. One visitor rapid-clicking could move the public count by more than ±1.Root cause
readLikeCount(pre-backfill) and backfill used row count instead of distinctipHashsetLikecalleddecrementLikeCountper removed duplicate, desyncinglikeCountsfrom realityFix
Cherry-pick of
d6e92c1(already validated oncursor/critical-correctness-bugs-605e):uniqueLikeCountsetLike,syncLikeCountForUrlsets the denormalized counter from source rows (also runs on idempotent retries, healing drift)scripts/like-unique-count-test.mjs(12 parallel toggles; global count must move ≤1)Validation
cursor/critical-bug-investigation-bc6dsetLike/readLikeCount/ backfill paths