Lost in Decoding? Reproducing and Stress-Testing the Look-Ahead Prior in Generative Retrieval

This repository contains code and experiment pipelines for three evaluation tracks:

1. RQ1: artifact-level PAG reproduction (released checkpoints + released identifiers).
2. RQ2: robustness under query perturbations.
3. RQ3: cross-lingual query shift and mitigation.

Correction to the RQ2 Results

[!IMPORTANT] The RQ2 results reported in Table 6 of the camera-ready paper have been corrected.

The original RQ2 experiments did not use the same decoding and evaluation path as the verified Table 3 reproduction. Consequently, the clean baselines in Table 6 were lower than the corresponding Table 3 results.

To correct this inconsistency, we re-decoded every RQ2 condition—both clean and perturbed—using the exact Table 3 pipeline:

• the same model checkpoint;
• the same lexical and semantic identifier files;
• the same --topk and --max_new_token_for_docid settings;
• the same --lex_constrained configuration; and
• the same two-stage constrained-decoding procedure.

All reported differences are calculated as

Δ = clean − perturbed

using the clean baseline produced by the corrected pipeline for the corresponding evaluation split. No clean value is copied from a different experiment or configuration.

[!NOTE] The correction does not change the findings or conclusions of the paper.

PAG remains sensitive to changes in query wording. Misspellings, synonym replacement, and paraphrasing consistently produce substantial retrieval-quality degradation, whereas word reordering and naturality normalization have considerably smaller effects.

The corrected values below have not yet been incorporated into the arXiv version of the paper. They will be included in a future revision.

Correction scope

The corrected evaluation covers:

• three evaluation splits: MS MARCO Dev, TREC-DL 2019, and TREC-DL 2020;
• five query variations: misspelling, reordering, synonym replacement, paraphrasing, and naturality;
• five perturbation seeds: 1999, 5, 27, 2016, and 2026.

In total, we re-decoded and re-evaluated:

• 75 perturbed runs: 3 splits × 5 variations × 5 seeds; and
• 3 clean runs, one for each split.

This gives 78 runs in total. The corrected clean results reproduce the Table 3 headline values within the small variation observed across repeated constrained-decoding runs.

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Corrected RQ2 Results

Unless otherwise stated, the tables report the mean and standard deviation over five perturbation seeds.

For each split:

Δ = corrected clean score − mean perturbed score

Before evaluation, each run is stably sorted by descending retrieval score and truncated to the top 10 results. NDCG@10 is computed using the released graded qrels, while Recall@10 and MRR@10 use the released binary qrels.

Note on decoding variability

[!NOTE] The constrained beam-search implementation used by this pipeline does not expose a decoding seed. As a result, repeated runs with identical inputs and settings may produce small differences in individual query rankings. Aggregate scores are generally stable within a few thousandths.

For this reason, all differences below use the clean score produced by the same corrected pipeline and configuration, rather than the clean score from the original Table 6 experiments.

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TREC-DL 2019

Corrected clean baseline: NDCG@10 = 0.7003, Recall@10 = 0.2650

---

TREC-DL 2020

Corrected clean baseline: NDCG@10 = 0.7021, Recall@10 = 0.2370

---

MS MARCO Dev

Corrected clean baseline: MRR@10 = 0.3856, Recall@10 = 0.6706

• The released naturality perturbation is identical across the five seed directories. It is a deterministic style-normalization transformation rather than a randomized perturbation. Consequently, the five evaluations produced identical aggregate scores in these experiments, resulting in zero measured seed variance.

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Summary of the Correction

The camera-ready RQ2 experiments reported a clean MS MARCO Dev MRR@10 of 0.362. After running RQ2 through the verified Table 3 pipeline, the corrected clean score is 0.386, consistent with the headline reproduction result.

The corrected results support the same overall conclusion as the camera-ready paper:

• misspellings cause the largest degradation across all three splits;
• synonym replacement and paraphrasing also produce substantial losses;
• word reordering has little or no effect on TREC-DL 2019, a small but consistent effect on MS MARCO Dev, and a modest effect on TREC-DL 2020, comparable in size to naturality normalization on that split; and
• naturality normalization produces relatively small degradation.

The numerical values in the camera-ready RQ2 table should therefore be replaced by the corrected results above. The interpretation of the experiment and the paper’s conclusion regarding PAG’s sensitivity to query variation remain unchanged.

Repository Layout

• t5_pretrainer/: core PAG model/training/inference codepaths.
• full_scripts/: legacy/full pipeline scripts used by RQ1-style runs.
• robustness/: RQ2 evaluation, perturbation generation, and aggregation.
• cross_lingual/: RQ3 evaluation and diagnostics.
• scripts/, tools/: utility scripts for efficiency and plotting.
• data/: datasets, checkpoints, and intermediate artifacts (not fully versioned).
• experiments/: run outputs (metrics, logs, summaries).

Quick Start

1. Environment

Use Conda (recommended):

source ~/miniconda3/etc/profile.d/conda.sh

# Main evaluation env
conda activate pag-env

# Optional (query-variation generation / dense-attack tooling)
# conda env create -f environment.yml
# conda activate pag-robustness

2. Verify Required Inputs

Expected core inputs:

data/experiments-full-lexical-ripor/lexical_ripor_direct_lng_knp_seq2seq_1/checkpoint/
data/experiments-full-lexical-ripor/t5-full-dense-1-5e-4-12l/aq_smtid/docid_to_tokenids.json
data/experiments-splade/t5-splade-0-12l/top_bow/docid_to_tokenids.json
data/msmarco-full/full_collection/
data/msmarco-full/dev_queries/raw.tsv
data/msmarco-full/dev_qrel.json
data/msmarco-full/TREC_DL_2019/
data/msmarco-full/TREC_DL_2020/

Quick check:

for p in \
  data/experiments-full-lexical-ripor/lexical_ripor_direct_lng_knp_seq2seq_1/checkpoint \
  data/experiments-full-lexical-ripor/t5-full-dense-1-5e-4-12l/aq_smtid/docid_to_tokenids.json \
  data/experiments-splade/t5-splade-0-12l/top_bow/docid_to_tokenids.json \
  data/msmarco-full/full_collection \
  data/msmarco-full/dev_queries/raw.tsv \
  data/msmarco-full/dev_qrel.json

do
  [ -e "$p" ] && echo "OK   $p" || echo "MISS $p"
done

Reproduction Entry Points

RQ1: PAG Artifact Reproduction

Run evaluation script:

bash full_scripts/full_lexical_ripor_evaluate.sh

Typical outputs:

• data/experiments-full-lexical-ripor/.../run.json
• evaluation json files (perf*.json)

RQ2: Robustness to Query Perturbations

[!TIP] To reproduce the corrected RQ2 values, decode the clean and perturbed query sets through the same verified Table 3 setup, then compute each Δ within that matched (clean, perturbed) pair.

Single run:

python -m robustness.evaluation.rq2 \
  --split dl19 \
  --attack_method mispelling \
  --seed 1999 \
  --n_gpu 1 \
  --batch_size 16 \
  --lex_topk 1000 \
  --smt_topk 100 \
  --output_dir experiments/RQ2_robustness

Batch launcher:

bash robustness/scripts/run_rq2_pipeline.sh

Aggregate:

python -m robustness.evaluation.aggregate_results \
  --results_dir experiments/RQ2_robustness \
  --splits dl19 dl20 dev \
  --attacks mispelling ordering synonym paraphrase naturality

See robustness/README.md for full details.

RQ3: Cross-Lingual Query Shift

Download multilingual queries:

bash cross_lingual/scripts/download_mmarco.sh --force

Run RQ3 (single language/split):

python -m cross_lingual.evaluation.rq3 \
  --language fr \
  --split dev \
  --n_gpu 1 \
  --batch_size 8

Batch launcher:

bash cross_lingual/scripts/run_rq3_pipeline.sh all all

Aggregate:

python -m cross_lingual.evaluation.aggregate_results \
  --results_dir experiments/RQ3_crosslingual

See cross_lingual/README.md for full details.

Observability and Run Validation

Use these checks to confirm runs progressed correctly:

1. Log files are created under each task's experiments/.../logs/ directory.
2. Per-run metric files exist (e.g., metrics_scores_and_asr.json, run.json, planner_tokens.json).
3. Aggregation commands emit summary.csv and summary.json.
4. Re-running aggregation does not change results unless upstream outputs changed.

Useful checks:

# Count generated run files
find experiments -name "run.json" | wc -l

# Confirm RQ2 summary exists
ls experiments/RQ2_robustness/summary*.csv

# Confirm RQ3 summary exists
ls experiments/RQ3_crosslingual/summary*.csv

[!TIP] Use fresh output directories for new experiments so old and corrected results are not mixed. When re-decoding into an existing experiment tree, guard against overwriting a prior run's output directory — reusing an output path across two different jobs can silently overwrite a prior run's outputs. A path-reuse issue of this kind affected the original RQ2 artifacts, so we re-decoded every condition into a fresh, isolated output tree.

Reproducibility Notes

[!TIP]

• Use fixed seeds where scripts provide them (1999, 5, 27, 2016, 2026).
• Keep lex_topk / smt_topk consistent when comparing runs.
• Record environment versions (conda env export > env_snapshot.yml) for archival.
• Always compare clean and perturbed runs from the same matched, re-decoded setup.
• Constrained beam decoding is unseeded; expect small run-to-run wobble in per-query rankings even with an identical config. Aggregate metrics are stable to within a few thousandths across repeats.

Metric Convention

[!NOTE] Metrics match the upstream PAG convention: a stable descending-score sort of the run truncated to the top 10, NDCG@10 computed on the graded qrels, and Recall@10 computed on the released binary qrels. The binary-qrel relevance threshold is per split as released: TREC-DL 2019 uses grade ≥ 2, TREC-DL 2020 uses grade ≥ 1. MS MARCO Dev uses its single released (binary) qrel file for both MRR@10 and Recall@10.

Troubleshooting

• ModuleNotFoundError: ensure you run from repository root and activate the correct conda env.
• Missing run.json: inspect SLURM stderr logs first; common causes are missing checkpoint/data paths.
• Empty aggregation output: verify all expected split/attack/seed combinations completed.
• OOM in evaluation: reduce --batch_size or run with fewer GPUs/processes.

Submodule Guides

• robustness/README.md: perturbation generation, RQ2 pipeline, dense-attack evaluation.
• cross_lingual/README.md: mMARCO setup, RQ3 execution, diagnostics, aggregation.
• cross_lingual/trained_extension/README.md: Trained extension workflow.

License

Apache 2.0. See LICENSE.

Upstream Work

This repository reproduces and stress-tests the PAG (Planner-Assisted Generative retrieval) system.

Paper:

Zeng, H., & Zamani, H. (2024). Planning Ahead in Generative Retrieval: Guiding Autoregressive Generation through Simultaneous Decoding. arXiv:2404.14600

Upstream repository:

https://github.com/HansiZeng/PAG

Our work builds directly on the released checkpoints and document identifiers from the upstream PAG repository. All three research questions (RQ1–RQ3) use the original PAG model as their baseline.