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int_proxy: VecReduceBackend records seeds as it draws novel records - #1016
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Fixes TimelyDataflow#994. `VecReduceBackend` drew a key's novel and prior records into one list and consolidated it. A `novel` flag in the sort key kept consolidation from netting a novel record against its history before the record's time was taken as a seed; the records were then netted by hand. The flag also sorted each value's prior records before its novel ones. With partially ordered times, advancing a prior record to `lower` can move it past a novel one: `(0, 5)` advances to `(1, 5)`, after a novel `(1, 0)`. The input bridge was then unsorted and unconsolidated, which fails `debug_assert_sorted_bridge`. Release builds gave correct output, because the tactic re-consolidates each value's edits. The walk now records the seeds as it draws the novel records, before anything is consolidated, as the `ReduceWindow` docs ask. The flag and the netting by hand are gone: one consolidation by `(data, time)` leaves each key's input sorted and netted. The regression test is Bryan O'Sullivan's, from TimelyDataflow#995. Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]> Claude-Session: https://claude.ai/code/session_019XsakwFGwtESwZ1gSYwG4o
This was referenced Oct 24, 2026
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Fixes #994.
VecReduceBackenddrew a key's novel and prior records into one list and consolidated it. Anovelflag in the sort key kept consolidation from netting a novel record against its history before the record's time was taken as a seed; the records were then netted by hand. The flag also sorted each value's prior records before its novel ones. With partially ordered times, advancing a prior record tolowercan move it past a novel one:(0, 5)advances to(1, 5), after a novel(1, 0). The input bridge was then unsorted and unconsolidated, which failsdebug_assert_sorted_bridge. Release builds gave correct output, because the tactic re-consolidates each value's edits.The walk now records the seeds as it draws the novel records, before anything is consolidated, as the
ReduceWindowdocs ask. The flag and the netting by hand are gone: one consolidation by(data, time)leaves each key's input sorted and netted.vec_backend.rsis +33/−41.The regression test,
reduce_prior_advanced_past_novel, is from #995.Checks
cargo test -p differential-dataflow: 149 passed.Product<u64, u64>times, in a debug build. On master-next, 1,339 of them fail the assertion; with this change, none do and all match.int_proxy_bench: no change beyond run-to-run noise.🤖 Generated with Claude Code
https://claude.ai/code/session_019XsakwFGwtESwZ1gSYwG4o