[FBumann]

Prompt: What about specsolve could we speed up?
Prompt: And do 2 as well maybe?

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A constant side over every dim of the constraint, whose table has exactly the constraint's rows in row order, is now attached by position instead of a group_by and a join. On main with #2065, nodal builds in 0.77× the time at its largest size and sector in 0.83×.

What changed and why it gives the same model

coverage.constant_side sums each constant piece per coordinate (constant_scalar, a group_by) and left-joins the result onto the rows. Now, for a piece whose dims are the constraint's dims, it first asks _aligned: does the piece have the same height as the rows, with key columns equal to the rows' key columns, row for row? The rows are one per coordinate, so then each row has exactly one value, and the sum and the join return that column unchanged. Any other piece takes the join as before:

• a piece over fewer dims than the constraint: a broadcast, or a partial sum such as sum(f, over=s), which keeps a row per summed label and can match the rows on its own dims while each row is owed several values;
• a piece with no dims under a constraint that has some (a sum to no dims);
• a piece with fewer rows than the constraint;
• the same coordinates in another order.

Every positional piece goes onto the rows before any join. A review found that a join ahead of a positional piece can reorder the rows: polars' streaming engine, which a build above IN_MEMORY_REACH uses, keeps no row order in a left join. x <= c + d over 300,000 rows, with c joined and d attached by position, gave row 0 a right-hand side of 75000 instead of 0. test_a_piece_attached_by_position_after_a_joined_one_lands_on_its_own_rows reproduced it as a strict xfail (6225c22) before the fix (1a299c8), which attaches the positional pieces in one with_columns on the collected rows rather than adding maintain_order to the joins.

The rows are collected once, and so is each piece over every dim of the constraint, which _aligned reads: if it does not align, the join reads the same materialised frame. A piece over fewer dims stays lazy for constant_scalar to sum, as on main (de6e98a, after a review found every piece collected). The per-piece gap columns that #2047 put on the rows pass are unchanged: a positional piece carries no null, because the door refuses a null value, and if one did reach it, it would be reported as a missing value rather than read as 0.

compiler.py has the same constant_scalar + left join for expressions. It is not touched here.

Probes and mutation table

tests/test_absence.py:

• test_a_constant_side_is_attached_by_position_only_where_its_coordinates_are_the_rows: six cases count how many pieces went through the sum and the join. Each case also checks that the LP file is byte-identical to one written with _aligned forced to None.
• test_a_sum_on_the_constant_side_is_never_attached_by_position: sum(c, over=t) over three values is a four-row piece on a four-row constraint.
• test_a_partial_sum_on_the_constant_side_is_owed_the_whole_sum: x <= sum(f, over=s) over (t, k), with as many s labels as k labels. A review found that the first version of this PR (gate if p.dims) solved it to 66 instead of 132, with no error, and the full suite stayed green. It was committed first as a strict xfail (1b39bd2). The gate is now set(p.dims) == set(c.dims) (6ed89c6), and the marker is off.
• test_a_piece_attached_by_position_after_a_joined_one_lands_on_its_own_rows: see above.

The dims gate in constant_side, by hand (sed on the one line, git checkout -- to restore, __pycache__ dropped on both sides, tree clean after each), taken at 6ed89c6:

mutation	test_absence.py	full suite (-x)
gate back to if p.dims (the bug)	caught, 1 failed	caught
gate dropped, every piece asked	caught, 2 failed	caught
gate never true	caught, 3 failed	caught

From the first version, on _aligned itself:

mutation	result
the alignment guard in _aligned deleted (tools/mutate.py)	caught
the guard keeps the height check and drops the key comparison (by hand)	caught, 2 failed
a positional piece attached after the joins ahead of it	caught, by the strict xfail run at 6225c22

Gates at de6e98a, on mathspec 0.4.0

No pixi in this container, so each gate ran in a uv environment synced from uv.lock (--group dev --group docs --all-extras, Python 3.12, polars 2.0.0), with Xpress 10.0.0 as CI now installs it:

• ruff check ., ruff format --check .: clean.
• pyrefly check on the package: 0 errors (at 1a299c8).
• pytest -q -n 4: 5892 passed, 458 skipped, 4 xfailed.
• pytest tests/test_docs_math.py tests/test_docstring_links.py (docs-test): 116 passed (at 1a299c8).

The head since is a merge of main after #2075; its tree differs from de6e98a only in CHANGELOG.md.

Not run: docs-build, the floors environment, test-via-pyarrow. The A/B below was taken at 30628c9, before the two fixes; they change only where the positional columns are added and which pieces are collected first, and were not re-measured.

A/B, build only (`sps.build`, no solver), this container (4 cores, not the publishing machine)

Base #2065's head 792d441, whose tree main has at 582e5c1; head 30628c9. One fresh process per measurement, base and head alternated ABBA for three rounds. Each process times sps.build 9 times (3 at l) and reports its minimum; the table gives the median of the three minima. Peak is ru_maxrss of the process. Load average 0.90 before, 1.98 after.

model	base ms	head ms	head ÷ base	head faster in	base peak MB	head peak MB
sector m (300k)	152.7	136.0	0.89	3/3	396	384
sector l (3M)	1545.6	1285.4	0.83	3/3	1303	1230
nodal l (3M)	345.1	264.2	0.77	3/3	857	740
network m (1M), control	264.2	264.0	1.00	1/3	599	566

Per-round minima, ms: sector m base 152.7 / 154.7 / 150.8, head 134.8 / 138.9 / 136.0; sector l base 1582.7 / 1545.6 / 1422.3, head 1266.8 / 1296.8 / 1285.4; nodal l base 318.4 / 348.3 / 345.1, head 291.4 / 257.9 / 264.2; network m base 264.2 / 264.8 / 258.3, head 266.6 / 263.9 / 264.0.

network's constant sides are sums through relations, so none is aligned and its time does not change. Three rounds per cell is below the six a sign test at 5% needs, so read the ratios with the per-round spread beside them.

#2022 makes constant_side return a lazy plan for one batched collect, and the eager collect of each piece over every dim here undoes part of that, so whichever of the two merges second needs a merge of the other and a re-measure.

🤖 Generated with Claude Code

https://claude.ai/code/session_018B3nA4oeSor7jjZ4vwux1G

Summary by CodeRabbit

• Performance
  • Improved processing of constraint values that align with their rows, avoiding unnecessary joins and potentially reducing work when generating optimization problems.
  • Values that don’t match row-for-row continue to use the existing handling, preserving behavior for reordered, broadcast, filtered, or partially summed data.

[read-the-docs-community]

Documentation build overview

📚 specsolve | 🛠️ Build #35556693 | 📁 Comparing 4c2d082 against latest (6e797ad)

  🔍 Preview build  

126 files changed · + 10 added · ± 114 modified · - 2 deleted

+ Added

• reference/changelog/index.html
• examples/pypsa_ladder/rung_61_voltage_angle_limits/index.html
• examples/pypsa_ladder/rung_62_startup_cost_per_snapshot/index.html
• examples/pypsa_ladder/rung_63_modular_branches_and_storage/index.html
• examples/pypsa_ladder/rung_64_commitment_edges/index.html
• examples/pypsa_ladder/rung_66_cycles_per_period/index.html
• examples/pypsa_ladder/rung_67_linearized_link_process/index.html
• examples/pypsa_ladder/rung_68_outage_factors_per_period/index.html
• examples/pypsa_ladder/rung_69_storage_retires_before_close/index.html
• examples/pypsa_ladder/rung_70_risk_preference_zero/index.html

± Modified

• index.html
• about/index.html
• run/index.html
• sweep/index.html
• about/benchmarks/index.html
• about/linopy/index.html
• development/architecture/index.html
• development/verification/index.html
• development/walkthrough/index.html
• examples/dispatch/index.html
• and 104 more...

- Deleted

• about/changelog/index.html
• examples/pypsa_ladder/rung_54_scenario_delay/index.html

[codspeed]

Merging this PR will improve performance by 61.58%

2 warnings

⚠️ 3 benchmarks with a significant change ran on different hardware

Their base and head results were measured on machines with a different CPU, core count or memory, so the changes might not come from the code. Run base and head on the same runner type.

Learn more about Macro Runners

See affected benchmarks

⚠️ 3 benchmarks with a significant change ran in a different software environment

Their base and head results were measured with a different OS or toolchain, such as compiler, runtime or library versions, so the changes might come from this difference rather than from the code. Open an affected benchmark to see what changed.

See affected benchmarks

⚡ 3 improved benchmarks
✅ 101 untouched benchmarks
⏩ 307 skipped benchmarks¹

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	test_read[commitment-s-specsolve-parquet]	684.3 KB	222.1 KB	×3.1
⚡	test_window[nodal-s-specsolve-highs-values]	3.2 MB	2.8 MB	+17.02%
⚡	test_window[nodal-s-specsolve-highs-one]	3.2 MB	2.8 MB	+17.02%

Tip

Curious why performance improved? Comment @codspeedbot explain why performance improved on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing perf/rhs-positional (4c2d082) with main (4e00952)²}

Footnotes

1. 307 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on main (93580b8) during the generation of this report, so 4e00952 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

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Walkthrough

constant_side now attaches constant-piece values by position when their collected rows match the constraint dimensions and row order. Other pieces continue through aggregation and a left join. Tests compare LP output across alignment, ordering, broadcasting, filtering, reductions, and streaming builds.

Changes: Constant-side row alignment

Layer / File(s)	Summary
Row-aligned constant assembly src/specsolve/_engine/coverage.py	constant_side checks collected constant-piece rows with _aligned. It attaches matching values by position and uses constant_scalar with a left join for pieces that do not match.
Alignment validation tests/test_absence.py, CHANGELOG.md	Tests compare positional attachment with coordinate joins for aligned, reordered, broadcast, filtered, and reduced pieces. A streaming-build test checks row alignment after a join. The changelog records the no-join case.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Refactor

Possibly related PRs

• fluxopt/specsolve#2022: Both PRs change coverage.constant_side; the lazy-plan and streaming-build changes may affect row-order assumptions.

Merge Risk: Minimal · previous review bfe94

No actionable merge-blocking risk remains in the reviewed change.

Security architecture risk: Low · up to de6e9

The positional path has explicit coordinate checks and retains aggregation for unmatched data. No expanded access or authority was identified. Remaining uncertainty concerns edge-case data handling and compatibility with the new minimum solver version, rather than an established security defect.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The direct integrity impact is on constraint right-hand sides in models built through this path, which then reach existing solver handoffs. The inspected production changes introduce no new identity, credential, or service-routing transition. Deployment-specific remote or cross-tenant exposure is not established by the supplied evidence.

Trust Boundaries and Controls

• observed — The positional eligibility checks enforce data association, not authorization: dimension sets must match, and coordinate columns must equal the constraint rows in sequence and height. Reduced-dimensional broadcasts, reordered coordinates, and nonmatching row counts use keyed aggregation instead.

Resilience and Maintainability Implications

• observed — Regression tests encode comparisons against the forced aggregation path, partial-sum behavior, and a 300,000-row mixed joined-and-positional case that checks each right-hand side against its own coordinate. These are inspected test assertions, not independently reproduced execution results.

Pre-merge checks: 5

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main performance change: reading aligned constant-side values by row position without a join.
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Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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Review comments at @src/specsolve/_engine/coverage.py:
- Line 151: Update both left joins in the piece-processing flow to pass
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[FBumann]

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The following content was generated by AI.

suite failed at d6ddc42 with 39 Xpress tests: xpress.DeprecationWarning: Deprecated in Xpress 10.0: use xpress.ObjSense.MAXIMIZE instead. It is not this PR's change: CI resolves Xpress 10.0.0, released 2026-10-29, and main fails the same way. The fix is #2075, ported here as 28be6c4 until it merges; the Xpress tests pass on Xpress 10.0.0 at that commit.

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Review comments at @src/specsolve/_engine/coverage.py:
- Line 146: Update the pieces construction to reuse each constant piece without
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