Formal models and scripts: legacy-int7-int4-scalar-quantized-scoring-fp-smt

Tools: Python

These are the working models and scripts this part of the hunt used. Some encode the code as it is (a counterexample is the expected result), others a fixed or correct variant; read the header comment of each file. Paths inside them were replaced by placeholders such as $LUCENE (a Lucene checkout) and $WORK.

Findings

• On main, a 9.x/10.x int7/int4 scalar-quantized segment whose vectors are all identical (stored quantiles equal) is decoded with the min == max widening that #14049 added, not the quantizer that wrote it, so its vectors read 127 (int7) or 15 (int4) units lower in every dimension and exact matches score about 0 and rank last (unreleased, 11.0 only) (finding LFV-841; repro · finding page)

Files

• legacy-sq-equal-quantiles-rewidened-on-read/model/sq_legacy_smt.py (used for LFV-841)

How to run

• Python: python3 <file>.py; scripts that import z3 need the z3-solver package.

Snapshot of 2026-11-04. AI-assisted; not yet triaged by a human Lucene committer. Feedback: open an issue in lucene-ai-bug-hunt.