{ "evaluation_id": "EVAL-20260402-142215", "question_id": "CODE-023", "question_text": "Write a database migration that adds a NOT NULL column with a default value to a table with 50 million rows in PostgreSQL — without locking the table or causing downtime. Explain the step-by-step process, why naive ALTER TABLE fails at scale, and how to verify data integrity after migration.", "category": "code", "timestamp": "2026-04-02T14:22:15.794Z", "display_date": "Apr 02, 2026", "winner": { "name": "GPT-5.4", "provider": "openrouter", "score": 8.79 }, "avg_score": 7.7, "matrix_size": 84, "models_used": [ { "id": "claude_opus_46", "name": "Claude Opus 4.6", "provider": "openrouter" }, { "id": "gemini_31_pro", "name": "Gemini 3.1 Pro", "provider": "openrouter" }, { "id": "claude_sonnet_46", "name": "Claude Sonnet 4.6", "provider": "openrouter" }, { "id": "grok_420", "name": "Grok 4.20", "provider": "openrouter" }, { "id": "gpt_oss_120b", "name": "GPT-OSS-120B", "provider": "OpenAI" }, { "id": "gemini_3_flash", "name": "Gemini 3 Flash Preview", "provider": "Google" }, { "id": "mimo_v2_flash", "name": "MiMo-V2-Flash", "provider": "Xiaomi" }, { "id": "gpt_5_4", "name": "GPT-5.4", "provider": "openrouter" }, { "id": "deepseek_v4", "name": "DeepSeek V4", "provider": "openrouter" }, { "id": "minimax_m25", "name": "MiniMax M2.5", "provider": "openrouter" } ], "rankings": { "gpt_5_4": { "display_name": "GPT-5.4", "provider": "openrouter", "average_score": 8.79, "score_count": 9, "min_score": 6, "max_score": 10, "rank": 1 }, "grok_420": { "display_name": "Grok 4.20", "provider": "openrouter", "average_score": 8.4, "score_count": 9, "min_score": 5.4, "max_score": 9.6, "rank": 2 }, "gemini_3_flash": { "display_name": "Gemini 3 Flash Preview", "provider": "Google", "average_score": 8.27, "score_count": 9, "min_score": 6.7, "max_score": 9.6, "rank": 3 }, "claude_sonnet_46": { "display_name": "Claude Sonnet 4.6", "provider": "openrouter", "average_score": 8.08, "score_count": 9, "min_score": 5.65, "max_score": 10, "rank": 4 }, "mimo_v2_flash": { "display_name": "MiMo-V2-Flash", "provider": "Xiaomi", "average_score": 7.96, "score_count": 9, "min_score": 6.05, "max_score": 9.6, "rank": 5 }, "claude_opus_46": { "display_name": "Claude Opus 4.6", "provider": "openrouter", "average_score": 7.74, "score_count": 9, "min_score": 4.45, "max_score": 10, "rank": 6 }, "gpt_oss_120b": { "display_name": "GPT-OSS-120B", "provider": "OpenAI", "average_score": 7.39, "score_count": 9, "min_score": 3.55, "max_score": 9.35, "rank": 7 }, "deepseek_v4": { "display_name": "DeepSeek V4", "provider": "openrouter", "average_score": 6.95, "score_count": 8, "min_score": 4.15, "max_score": 8.6, "rank": 8 }, "minimax_m25": { "display_name": "MiniMax M2.5", "provider": "openrouter", "average_score": 6.76, "score_count": 4, "min_score": 0.5, "max_score": 9.35, "rank": 9 }, "gemini_31_pro": { "display_name": "Gemini 3.1 Pro", "provider": "openrouter", "average_score": 6.66, "score_count": 9, "min_score": 4.35, "max_score": 8.8, "rank": 10 } }, "judgments": [ { "judge_key": "gpt_5_4", "judge_name": "GPT-5.4", "respondent_key": "claude_opus_46", "respondent_name": "Claude Opus 4.6", "weighted_score": 4.45, "brief_justification": "Clear structure and mostly correct early steps, but the response is truncated before the crucial batch backfill, constraint-validation, and integrity-verification details. It also contains inaccuracies about locking/NOT NULL behavior and overstates some version nuances." }, { "judge_key": "gpt_5_4", "judge_name": "GPT-5.4", "respondent_key": "gemini_31_pro", "respondent_name": "Gemini 3.1 Pro", "weighted_score": 4.35, "brief_justification": "Starts correctly with the important PostgreSQL 11+ caveat, but the response is truncated and does not deliver the requested step-by-step migration, locking details, or integrity verification. Partially accurate but incomplete and only moderately clear/useful." }, { "judge_key": "gpt_5_4", "judge_name": "GPT-5.4", "respondent_key": "claude_sonnet_46", "respondent_name": "Claude Sonnet 4.6", "weighted_score": 5.8, "brief_justification": "Explains the general phased approach and version caveat well, but contains important PostgreSQL inaccuracies: ADD COLUMN takes ACCESS EXCLUSIVE lock, NOT NULL cannot be added as NOT VALID directly, and the PL/pgSQL backfill function cannot commit per batch as implied. The response is also truncated before finishing verification/integrity steps." }, { "judge_key": "gpt_5_4", "judge_name": "GPT-5.4", "respondent_key": "grok_420", "respondent_name": "Grok 4.20", "weighted_score": 7.5, "brief_justification": "Clear and practical step-by-step guidance with good verification advice, but it contains notable PostgreSQL inaccuracies: adding a column with a constant default is metadata-only in PostgreSQL 11+, so the naive statement does not necessarily rewrite 50M rows; the DO-block example uses UPDATE ... LIMIT, which PostgreSQL does not support directly; and ALTER COLUMN SET NOT NULL can still require a full table scan and is not guaranteed to be <100ms. Overall useful, but correctness is weakened by the" }, { "judge_key": "gpt_5_4", "judge_name": "GPT-5.4", "respondent_key": "gpt_oss_120b", "respondent_name": "GPT-OSS-120B", "weighted_score": 5.8, "brief_justification": "Clear structure and some sound guidance, but it contains important inaccuracies about locking and the naive ALTER behavior, and the migration is incomplete/truncated with questionable SQL guidance like UPDATE ... LIMIT wording and oversimplified zero-downtime claims." }, { "judge_key": "gpt_5_4", "judge_name": "GPT-5.4", "respondent_key": "gemini_3_flash", "respondent_name": "Gemini 3 Flash Preview", "weighted_score": 7.7, "brief_justification": "Well-structured and mostly practical, with strong explanation of phased backfill and validation. However, it contains important PostgreSQL inaccuracies around locking and semantics: ADD COLUMN DEFAULT in PG11+ means old rows read as the default rather than becoming NULL, NOT VALID CHECK does not fully behave like NOT NULL for all planner/semantic purposes, lock names are misstated, and claiming SET NOT NULL can skip the scan based on a validated CHECK is version-sensitive and not universally saf" }, { "judge_key": "gpt_5_4", "judge_name": "GPT-5.4", "respondent_key": "mimo_v2_flash", "respondent_name": "MiMo-V2-Flash", "weighted_score": 6.35, "brief_justification": "Well-structured and mostly clear, with a solid phased approach and good explanation of why naive ALTER can be problematic. However, it contains important inaccuracies: DO blocks do not auto-commit per loop iteration, pg_repack usage shown is dubious, 'temporary table during validation' is incorrect, and the handling of NOT NULL vs CHECK NOT VALID is somewhat misleading. It also omits the modern PostgreSQL 11+ fast-path option of adding the column with a constant DEFAULT first, then backfilling o" }, { "judge_key": "claude_opus_46", "judge_name": "Claude Opus 4.6", "respondent_key": "gpt_5_4", "respondent_name": "GPT-5.4", "weighted_score": 9.35, "brief_justification": "Excellent, production-grade response that accurately covers the phased migration strategy for adding a NOT NULL column to a large PostgreSQL table. The explanation of why naive ALTER TABLE is dangerous is correct and nuanced, including the PG11+ optimization note. The step-by-step process is thorough: nullable column addition, default setting, batched backfill with sleep, NOT VALID constraint, validation, and optional NOT NULL finalization. Data integrity verification is comprehensive with concr" }, { "judge_key": "claude_opus_46", "judge_name": "Claude Opus 4.6", "respondent_key": "gemini_31_pro", "respondent_name": "Gemini 3.1 Pro", "weighted_score": 6.55, "brief_justification": "The response starts very well with an important and correct distinction about PG 11+ behavior for constant defaults, which many guides miss. The explanation of why naive ALTER TABLE fails is accurate. However, the response is clearly truncated mid-sentence - it cuts off during the MVCC explanation and never delivers the promised multi-step migration strategy, the verification steps, or the complete step-by-step process. The content that exists is correct and well-structured, but the incompletene" }, { "judge_key": "claude_opus_46", "judge_name": "Claude Opus 4.6", "respondent_key": "claude_sonnet_46", "respondent_name": "Claude Sonnet 4.6", "weighted_score": 7, "brief_justification": "The response demonstrates good understanding of the problem and provides a well-structured approach. However, there are notable issues: (1) For PostgreSQL 11+, adding a column with a constant DEFAULT no longer rewrites the table, which the response acknowledges but then still recommends the multi-step approach without clearly distinguishing when it's necessary vs. optional. (2) The claim that NOT NULL 'still causes full table scan for validation' on PG 11+ is misleading - if the default is set i" }, { "judge_key": "claude_opus_46", "judge_name": "Claude Opus 4.6", "respondent_key": "grok_420", "respondent_name": "Grok 4.20", "weighted_score": 7.95, "brief_justification": "The response is well-structured and covers the key concepts thoroughly. However, there are some correctness issues: (1) In PostgreSQL 11+, ADD COLUMN with a non-volatile DEFAULT is actually metadata-only and does NOT rewrite the table - the naive approach description is partially outdated/misleading for PG11+. The response claims the naive ALTER TABLE rewrites the table, which is true for PG <11 but not for PG 11+ with a constant default. (2) The DO block uses UPDATE...LIMIT which is not valid P" }, { "judge_key": "claude_opus_46", "judge_name": "Claude Opus 4.6", "respondent_key": "deepseek_v4", "respondent_name": "DeepSeek V4", "weighted_score": 5.6, "brief_justification": "The response has a significant correctness issue: since PostgreSQL 11, ALTER TABLE ADD COLUMN with a non-volatile DEFAULT is metadata-only and does NOT rewrite the table. The premise that a naive ALTER TABLE rewrites all rows is outdated. The batched update approach using COMMIT inside a DO block won't work as shown (COMMIT isn't allowed in a DO block without explicit transaction control via procedures in PG 11+). The response also misses the NOT VALID CHECK constraint approach for adding NOT NU" }, { "judge_key": "claude_opus_46", "judge_name": "Claude Opus 4.6", "respondent_key": "gpt_oss_120b", "respondent_name": "GPT-OSS-120B", "weighted_score": 6.2, "brief_justification": "The response is well-structured and covers the general approach correctly, but contains a significant factual error: in PostgreSQL 11+, `ALTER TABLE ADD COLUMN ... NOT NULL DEFAULT 'foo'` does NOT scan all rows or cause a long lock — it's a metadata-only operation. The claim that NOT NULL forces a full scan during ADD COLUMN with a default is incorrect for PG 11+. The multi-step approach described is valid for PG <11 or for cases without defaults, but the 'why naive ALTER TABLE fails' section is" }, { "judge_key": "claude_opus_46", "judge_name": "Claude Opus 4.6", "respondent_key": "gemini_3_flash", "respondent_name": "Gemini 3 Flash Preview", "weighted_score": 7.95, "brief_justification": "The response is well-structured and covers the key steps thoroughly. However, there are some correctness issues: (1) In PG 11+, ADD COLUMN with a constant DEFAULT is metadata-only and rows won't have NULLs during the 'split-second migration' - the explanation for why backfilling is needed is misleading. (2) The lock type 'SHARE COMBINED' doesn't exist in PostgreSQL - the correct lock for adding a NOT VALID CHECK constraint is ShareUpdateExclusiveLock (PG 12+) or AccessExclusiveLock briefly. (3) " }, { "judge_key": "claude_opus_46", "judge_name": "Claude Opus 4.6", "respondent_key": "minimax_m25", "respondent_name": "MiniMax M2.5", "weighted_score": 0.5, "brief_justification": "The response is completely empty/blank. No content was provided to address the question about PostgreSQL database migration strategies for large tables." }, { "judge_key": "claude_opus_46", "judge_name": "Claude Opus 4.6", "respondent_key": "mimo_v2_flash", "respondent_name": "MiMo-V2-Flash", "weighted_score": 7.95, "brief_justification": "The response is well-structured and covers the key concepts thoroughly. However, there are several correctness issues: (1) In PostgreSQL 11+, ALTER TABLE ADD COLUMN with a non-volatile DEFAULT does NOT require a table rewrite even with NOT NULL - it's a metadata-only operation, which undermines the premise of the entire multi-step approach for PG 11+. The response acknowledges PG 11+ but then contradicts itself by suggesting the naive approach still fails. (2) The DO block with ctid-based batchi" }, { "judge_key": "gemini_31_pro", "judge_name": "Gemini 3.1 Pro", "respondent_key": "gpt_5_4", "respondent_name": "GPT-5.4", "weighted_score": 6, "brief_justification": "" }, { "judge_key": "gemini_31_pro", "judge_name": "Gemini 3.1 Pro", "respondent_key": "claude_opus_46", "respondent_name": "Claude Opus 4.6", "weighted_score": 4.7, "brief_justification": "" }, { "judge_key": "gemini_31_pro", "judge_name": "Gemini 3.1 Pro", "respondent_key": "claude_sonnet_46", "respondent_name": "Claude Sonnet 4.6", "weighted_score": 5.65, "brief_justification": "" }, { "judge_key": "gemini_31_pro", "judge_name": "Gemini 3.1 Pro", "respondent_key": "grok_420", "respondent_name": "Grok 4.20", "weighted_score": 5.4, "brief_justification": "" }, { "judge_key": "gemini_31_pro", "judge_name": "Gemini 3.1 Pro", "respondent_key": "deepseek_v4", "respondent_name": "DeepSeek V4", "weighted_score": 4.15, "brief_justification": "" }, { "judge_key": "gemini_31_pro", "judge_name": "Gemini 3.1 Pro", "respondent_key": "gpt_oss_120b", "respondent_name": "GPT-OSS-120B", "weighted_score": 3.55, "brief_justification": "" }, { "judge_key": "gemini_31_pro", "judge_name": "Gemini 3.1 Pro", "respondent_key": "gemini_3_flash", "respondent_name": "Gemini 3 Flash Preview", "weighted_score": 6.7, "brief_justification": "" }, { "judge_key": "gemini_31_pro", "judge_name": "Gemini 3.1 Pro", "respondent_key": "mimo_v2_flash", "respondent_name": "MiMo-V2-Flash", "weighted_score": 7.2, "brief_justification": "" }, { "judge_key": "claude_sonnet_46", "judge_name": "Claude Sonnet 4.6", "respondent_key": "gpt_5_4", "respondent_name": "GPT-5.4", "weighted_score": 9, "brief_justification": "Excellent, comprehensive response covering all key aspects: why naive ALTER TABLE fails, phased migration strategy, batched backfill with code examples, NOT VALID constraint pattern, data integrity verification, and operational safeguards. Correctly notes PG11+ optimization. Minor issue: response appears truncated at the end (CREATE INDEX CON...). The NOT VALID + VALIDATE approach is correctly explained. Very practical and actionable with good depth on lock behavior and operational concerns." }, { "judge_key": "claude_sonnet_46", "judge_name": "Claude Sonnet 4.6", "respondent_key": "claude_opus_46", "respondent_name": "Claude Opus 4.6", "weighted_score": 8.6, "brief_justification": "Excellent technical depth with accurate PostgreSQL version nuances, clear diagrams, and well-structured step-by-step approach. The response is cut off before completing Step 3 (batched backfill), Step 4 (NOT NULL constraint), and Step 5 (verification), which significantly impacts completeness. What is present is highly accurate and practical, including lock_timeout safety, PG11+ optimizations, and the reasoning behind each step." }, { "judge_key": "claude_sonnet_46", "judge_name": "Claude Sonnet 4.6", "respondent_key": "gemini_31_pro", "respondent_name": "Gemini 3.1 Pro", "weighted_score": 6.3, "brief_justification": "The response starts strong with accurate information about PG 11+ optimization and correctly identifies when the naive approach fails. However, the response is clearly truncated mid-sentence, cutting off the explanation of MVCC and missing the entire multi-step migration strategy, the locking explanation, and the data integrity verification steps — which were core parts of the question. What exists is accurate and well-structured, but the incomplete response significantly reduces completeness, d" }, { "judge_key": "claude_sonnet_46", "judge_name": "Claude Sonnet 4.6", "respondent_key": "grok_420", "respondent_name": "Grok 4.20", "weighted_score": 8.8, "brief_justification": "Excellent response covering the naive failure mode, step-by-step zero-downtime strategy, batch backfill with SKIP LOCKED, NOT VALID constraint approach, and comprehensive integrity verification. Minor issues: Step 4 claim that SET NOT NULL is 'validation-only' after backfill is slightly optimistic (it still takes ACCESS EXCLUSIVE lock and scans the table), and the NOT VALID approach is available in PostgreSQL 11+ not just 12+. The LIMIT clause in a plain UPDATE without ORDER BY is also non-stand" }, { "judge_key": "claude_sonnet_46", "judge_name": "Claude Sonnet 4.6", "respondent_key": "deepseek_v4", "respondent_name": "DeepSeek V4", "weighted_score": 7.35, "brief_justification": "The response is well-structured and covers the core approach correctly. However, it misses a critical PostgreSQL optimization: since PostgreSQL 11+, adding a column with a non-volatile DEFAULT no longer rewrites the table, making the naive approach less problematic than described for modern versions. The batch update script has a bug — COMMIT inside a DO block requires a procedure, not a plain DO block in older PostgreSQL. The response also misses important details like using pg_sleep between ba" }, { "judge_key": "claude_sonnet_46", "judge_name": "Claude Sonnet 4.6", "respondent_key": "gpt_oss_120b", "respondent_name": "GPT-OSS-120B", "weighted_score": 8, "brief_justification": "The response is well-structured, technically accurate, and provides a practical step-by-step migration plan. It correctly explains why naive ALTER TABLE is problematic and offers a zero-downtime approach. Minor issues: the response appears truncated (the bash script cuts off mid-comment), and the claim that NOT NULL forces a full scan even in PG 11+ is slightly oversimplified (PG 11+ stores the default without rewrite, but NOT NULL validation still requires a scan). The table-based TL;DR is exce" }, { "judge_key": "claude_sonnet_46", "judge_name": "Claude Sonnet 4.6", "respondent_key": "gemini_3_flash", "respondent_name": "Gemini 3 Flash Preview", "weighted_score": 8.55, "brief_justification": "The response is well-structured and covers the zero-downtime migration strategy comprehensively. The step-by-step approach is correct and practical. Minor issues: Step 2 is redundant since Step 1 already sets the default; the claim about 'SHARE COMBINED' lock in Step 4 is inaccurate (it should be SHARE ROW EXCLUSIVE); and the backfill explanation slightly overstates the null risk with PostgreSQL 11+ defaults. Step 6's note about Postgres 12+ skipping the scan when a CHECK constraint exists is ac" }, { "judge_key": "claude_sonnet_46", "judge_name": "Claude Sonnet 4.6", "respondent_key": "mimo_v2_flash", "respondent_name": "MiMo-V2-Flash", "weighted_score": 8.35, "brief_justification": "The response is comprehensive and largely accurate, covering the key steps for a zero-downtime migration. It correctly explains the naive ALTER TABLE failure, the batched backfill approach, and the NOT VALID constraint trick. Minor issues: the DO block doesn't actually commit between iterations (a real script would need explicit commits outside a transaction), and the response slightly conflates SET NOT NULL with CHECK constraints. The cleanup section has a minor redundancy (VALIDATE CONSTRAINT " }, { "judge_key": "grok_420", "judge_name": "Grok 4.20", "respondent_key": "gpt_5_4", "respondent_name": "GPT-5.4", "weighted_score": 8.8, "brief_justification": "The response is factually accurate, logically sound, and provides a thorough, well-structured, phased approach for safe PostgreSQL migration on large tables. It explains risks clearly, offers practical code examples, and covers verification comprehensively. Minor deduction for an incomplete index command at the end and slight redundancy in explanations." }, { "judge_key": "grok_420", "judge_name": "Grok 4.20", "respondent_key": "claude_opus_46", "respondent_name": "Claude Opus 4.6", "weighted_score": 8.45, "brief_justification": "The response is factually accurate on PostgreSQL behavior (with minor version nuance simplifications), provides a clear, well-structured multi-step process with diagrams, explains why the naive approach fails, and covers verification implicitly. It is highly practical for production use, though the backfill step is truncated and could include more on constraint validation and cleanup." }, { "judge_key": "grok_420", "judge_name": "Grok 4.20", "respondent_key": "gemini_31_pro", "respondent_name": "Gemini 3.1 Pro", "weighted_score": 6.6, "brief_justification": "Response provides good overview of PG11+ optimization and why naive ALTER fails, but is incomplete as it cuts off mid-sentence and lacks the full multi-step process, verification steps, and full explanation requested." }, { "judge_key": "grok_420", "judge_name": "Grok 4.20", "respondent_key": "claude_sonnet_46", "respondent_name": "Claude Sonnet 4.6", "weighted_score": 8.65, "brief_justification": "The response is factually accurate on PostgreSQL behaviors (especially PG11+), provides a solid zero-downtime strategy with detailed code, and explains tradeoffs well. Minor incompleteness: the provided backfill function has a logic issue with how it advances the cursor (it increments by batch_size regardless of actual rows processed or gaps), and the final monitoring query is cut off. Depth on internals and verification steps is strong overall." }, { "judge_key": "grok_420", "judge_name": "Grok 4.20", "respondent_key": "deepseek_v4", "respondent_name": "DeepSeek V4", "weighted_score": 6.6, "brief_justification": "The response is mostly correct but contains inaccuracies: the batch update script has a flawed loop structure and unnecessary COMMIT inside DO block; the final ALTER COLUMN SET NOT NULL still rewrites the table (though faster); it omits the more optimal trigger-based or concurrent index methods. Completeness is decent with good verification steps. Clarity is high due to structure. Depth is moderate, missing some advanced PostgreSQL 11+ options like ADD COLUMN with DEFAULT without rewrite in newe" }, { "judge_key": "grok_420", "judge_name": "Grok 4.20", "respondent_key": "gpt_oss_120b", "respondent_name": "GPT-OSS-120B", "weighted_score": 8.6, "brief_justification": "The response is factually accurate for PostgreSQL 11+, provides a clear step-by-step zero-downtime approach, explains why the naive method fails, and includes practical scripts. Minor deduction for completeness as the backfill script is truncated and verification steps for data integrity are missing despite being requested." }, { "judge_key": "grok_420", "judge_name": "Grok 4.20", "respondent_key": "gemini_3_flash", "respondent_name": "Gemini 3 Flash Preview", "weighted_score": 7.95, "brief_justification": "The response is mostly accurate and provides a solid zero-downtime approach, but contains a significant technical error in Step 4/5: you cannot add a CHECK constraint as a substitute for NOT NULL in this manner, and the final ALTER ... SET NOT NULL will still require a full table scan in most Postgres versions. The rest of the steps, explanations, and verification are clear, thorough, and practical." }, { "judge_key": "grok_420", "judge_name": "Grok 4.20", "respondent_key": "minimax_m25", "respondent_name": "MiniMax M2.5", "weighted_score": 8.6, "brief_justification": "The response accurately details a robust zero-downtime migration strategy using add column with default, backfill in batches, and constraint addition. It explains why naive ALTER TABLE causes issues at scale (though briefly), provides practical steps, and covers verification. Minor omission of explicit trigger or default handling nuances, but overall excellent." }, { "judge_key": "grok_420", "judge_name": "Grok 4.20", "respondent_key": "mimo_v2_flash", "respondent_name": "MiMo-V2-Flash", "weighted_score": 6.05, "brief_justification": "The response has several technical inaccuracies (e.g. incorrect use of ALTER COLUMN SET NOT NULL with NOT VALID, redundant VALIDATE steps, flawed DO block, pg_repack command syntax), incomplete coverage of verification, and some misleading claims about locking behavior, though the overall strategy is conceptually sound and clearly explained." }, { "judge_key": "deepseek_v4", "judge_name": "DeepSeek V4", "respondent_key": "gpt_5_4", "respondent_name": "GPT-5.4", "weighted_score": 10, "brief_justification": "Comprehensive, accurate, and well-structured response covering all aspects of the migration process, including detailed steps, rationale, and verification methods." }, { "judge_key": "deepseek_v4", "judge_name": "DeepSeek V4", "respondent_key": "claude_opus_46", "respondent_name": "Claude Opus 4.6", "weighted_score": 10, "brief_justification": "Comprehensive, accurate, and clear explanation with detailed steps and rationale." }, { "judge_key": "deepseek_v4", "judge_name": "DeepSeek V4", "respondent_key": "gemini_31_pro", "respondent_name": "Gemini 3.1 Pro", "weighted_score": 8.6, "brief_justification": "Accurate and detailed, but slightly incomplete as it cuts off mid-sentence." }, { "judge_key": "deepseek_v4", "judge_name": "DeepSeek V4", "respondent_key": "claude_sonnet_46", "respondent_name": "Claude Sonnet 4.6", "weighted_score": 9.6, "brief_justification": "Highly accurate and thorough with excellent practical value." }, { "judge_key": "deepseek_v4", "judge_name": "DeepSeek V4", "respondent_key": "grok_420", "respondent_name": "Grok 4.20", "weighted_score": 9.6, "brief_justification": "Comprehensive, accurate, and highly practical with excellent detail and verification steps." }, { "judge_key": "deepseek_v4", "judge_name": "DeepSeek V4", "respondent_key": "gpt_oss_120b", "respondent_name": "GPT-OSS-120B", "weighted_score": 9.35, "brief_justification": "Highly accurate, thorough, and clear with excellent practical value." }, { "judge_key": "deepseek_v4", "judge_name": "DeepSeek V4", "respondent_key": "gemini_3_flash", "respondent_name": "Gemini 3 Flash Preview", "weighted_score": 9.6, "brief_justification": "Highly accurate, thorough, and practical with clear explanations and deep insights." }, { "judge_key": "deepseek_v4", "judge_name": "DeepSeek V4", "respondent_key": "minimax_m25", "respondent_name": "MiniMax M2.5", "weighted_score": 8.6, "brief_justification": "Detailed and accurate with clear steps and good depth on verification." }, { "judge_key": "deepseek_v4", "judge_name": "DeepSeek V4", "respondent_key": "mimo_v2_flash", "respondent_name": "MiMo-V2-Flash", "weighted_score": 9.6, "brief_justification": "Highly accurate, thorough, and practical with excellent clarity and depth." }, { "judge_key": "gpt_oss_120b", "judge_name": "GPT-OSS-120B", "respondent_key": "gpt_5_4", "respondent_name": "GPT-5.4", "weighted_score": 8.8, "brief_justification": "Accurate migration steps, covers why naive ALTER fails, detailed batch backfill, constraint handling, verification queries, and operational tips; well-structured and practical." }, { "judge_key": "gpt_oss_120b", "judge_name": "GPT-OSS-120B", "respondent_key": "claude_opus_46", "respondent_name": "Claude Opus 4.6", "weighted_score": 7.25, "brief_justification": "Accurate explanation of lock behavior and multi-step migration, well-structured and insightful, but missing full backfill and final steps, and contains minor version detail inaccuracies." }, { "judge_key": "gpt_oss_120b", "judge_name": "GPT-OSS-120B", "respondent_key": "gemini_31_pro", "respondent_name": "Gemini 3.1 Pro", "weighted_score": 5.25, "brief_justification": "The answer correctly notes PG 11+ optimization and why naive ALTER can be problematic, but it is truncated and lacks the full step-by-step migration process and verification steps, reducing completeness and overall usefulness." }, { "judge_key": "gpt_oss_120b", "judge_name": "GPT-OSS-120B", "respondent_key": "claude_sonnet_46", "respondent_name": "Claude Sonnet 4.6", "weighted_score": 8.8, "brief_justification": "Accurate explanation of PostgreSQL internals, thorough step-by-step migration with code, clear formatting, insightful batching technique, and practical verification steps." }, { "judge_key": "gpt_oss_120b", "judge_name": "GPT-OSS-120B", "respondent_key": "grok_420", "respondent_name": "Grok 4.20", "weighted_score": 8.8, "brief_justification": "Accurate step-by-step migration plan, thorough coverage of pitfalls and verification, clearly presented with practical scripts and optional optimizations." }, { "judge_key": "gpt_oss_120b", "judge_name": "GPT-OSS-120B", "respondent_key": "deepseek_v4", "respondent_name": "DeepSeek V4", "weighted_score": 7.75, "brief_justification": "Provides a clear, step-by-step safe migration plan and explains why naive ALTER fails, but contains some technical inaccuracies (e.g., committing inside a DO block) that affect full correctness." }, { "judge_key": "gpt_oss_120b", "judge_name": "GPT-OSS-120B", "respondent_key": "gemini_3_flash", "respondent_name": "Gemini 3 Flash Preview", "weighted_score": 8.6, "brief_justification": "Accurate step-by-step zero-downtime migration with correct concepts, well-structured and actionable; minor nuances about lock types could be clearer, but overall highly useful." }, { "judge_key": "gpt_oss_120b", "judge_name": "GPT-OSS-120B", "respondent_key": "mimo_v2_flash", "respondent_name": "MiMo-V2-Flash", "weighted_score": 8.55, "brief_justification": "Accurate overall with minor technical slips; covers all needed steps and explains internals clearly; well-structured and actionable for a large table migration." }, { "judge_key": "gemini_3_flash", "judge_name": "Gemini 3 Flash Preview", "respondent_key": "gpt_5_4", "respondent_name": "GPT-5.4", "weighted_score": 9.6, "brief_justification": "The response provides a highly professional, production-grade strategy for large-scale migrations. It correctly identifies the risks of naive ALTER TABLE, explains the PG11+ optimization, and provides a robust multi-step process including batched backfills and NOT VALID constraints. The inclusion of verification steps and operational safeguards like monitoring replication lag adds significant value." }, { "judge_key": "gemini_3_flash", "judge_name": "Gemini 3 Flash Preview", "respondent_key": "claude_opus_46", "respondent_name": "Claude Opus 4.6", "weighted_score": 9.6, "brief_justification": "The response is exceptionally clear and technically accurate. It correctly identifies the nuances between PostgreSQL versions (pre-11 vs post-11) and provides a robust, industry-standard multi-step strategy for 50M rows. While the backfill script was cut off at the very end, the architectural explanation and initial steps are perfect." }, { "judge_key": "gemini_3_flash", "judge_name": "Gemini 3 Flash Preview", "respondent_key": "gemini_31_pro", "respondent_name": "Gemini 3.1 Pro", "weighted_score": 7.75, "brief_justification": "The response starts very strong, correctly identifying the PG 11+ optimization for constant defaults. However, the response is incomplete; it cuts off mid-sentence while explaining MVCC and fails to provide the promised multi-step strategy or verification steps." }, { "judge_key": "gemini_3_flash", "judge_name": "Gemini 3 Flash Preview", "respondent_key": "claude_sonnet_46", "respondent_name": "Claude Sonnet 4.6", "weighted_score": 10, "brief_justification": "This is an exceptional response. It correctly identifies the nuances of PostgreSQL versions (11+), provides a robust batched backfill strategy with ID-based iteration (which is the industry standard for large tables), includes monitoring queries, and explains the locking mechanics perfectly. The use of 'FOR UPDATE SKIP LOCKED' and 'pg_sleep' shows high-level expertise in database reliability engineering." }, { "judge_key": "gemini_3_flash", "judge_name": "Gemini 3 Flash Preview", "respondent_key": "grok_420", "respondent_name": "Grok 4.20", "weighted_score": 9.55, "brief_justification": "The response is excellent and provides a production-ready strategy. It correctly identifies that since Postgres 11, adding a column with a default is actually fast, but the batching strategy is still the safest way to handle the NOT NULL constraint and backfilling on massive tables without bloat or long-held locks. The inclusion of SKIP LOCKED and validation steps shows high technical depth." }, { "judge_key": "gemini_3_flash", "judge_name": "Gemini 3 Flash Preview", "respondent_key": "deepseek_v4", "respondent_name": "DeepSeek V4", "weighted_score": 7.55, "brief_justification": "The response provides a solid practical strategy for large-scale migrations. However, it misses a critical PostgreSQL optimization: since PG 11, adding a column with a constant DEFAULT is a metadata-only change and does not require a table rewrite. The suggested batch update is logically sound but technically unnecessary for modern PG versions. Additionally, the provided PL/pgSQL block with COMMIT will fail in standard PG scripts unless run as a PROCEDURE, as COMMIT is not allowed in DO blocks i" }, { "judge_key": "gemini_3_flash", "judge_name": "Gemini 3 Flash Preview", "respondent_key": "gpt_oss_120b", "respondent_name": "GPT-OSS-120B", "weighted_score": 9.15, "brief_justification": "The response is excellent and highly practical. It correctly identifies that while PG11+ optimized defaults, the NOT NULL constraint still requires a scan. The batching strategy using CTIDs is a professional-grade solution for large-scale migrations. The response was slightly cut off at the very end of the script, but the core logic and all steps were fully explained." }, { "judge_key": "gemini_3_flash", "judge_name": "Gemini 3 Flash Preview", "respondent_key": "mimo_v2_flash", "respondent_name": "MiMo-V2-Flash", "weighted_score": 9.55, "brief_justification": "The response is excellent and provides a highly practical, industry-standard approach to a complex database operation. It correctly identifies the locking behavior of PostgreSQL and provides a safe, multi-step workaround using batching and NOT VALID constraints. One minor technical note: in Postgres 11+, adding a column with a constant default no longer requires a full table rewrite, but the response correctly notes that the NOT NULL constraint validation still causes the primary locking issue a" }, { "judge_key": "minimax_m25", "judge_name": "MiniMax M2.5", "respondent_key": "gpt_5_4", "respondent_name": "GPT-5.4", "weighted_score": 8.6, "brief_justification": "Technically accurate and thorough explanation of the phased migration approach. Covers why naive ALTER TABLE fails, provides step-by-step SQL, batch backfill examples with ctid, constraint validation strategy, and verification queries. Slight deduction for incomplete ending (CREATE INDEX truncated) and minor clarity issues." }, { "judge_key": "minimax_m25", "judge_name": "MiniMax M2.5", "respondent_key": "claude_opus_46", "respondent_name": "Claude Opus 4.6", "weighted_score": 7.6, "brief_justification": "Technically accurate and well-structured with excellent diagrams explaining lock behavior and migration steps. However, the response is incomplete - it cuts off mid-Step 3 (batch backfill) and never shows the remaining steps (adding NOT NULL constraint, verification). The user cannot fully implement the solution from this response." }, { "judge_key": "minimax_m25", "judge_name": "MiniMax M2.5", "respondent_key": "gemini_31_pro", "respondent_name": "Gemini 3.1 Pro", "weighted_score": 5.75, "brief_justification": "Response provides accurate information about PG 11+ optimization but is severely incomplete - cuts off mid-explanation before covering the step-by-step process, verification steps, and the full technical explanation promised." }, { "judge_key": "minimax_m25", "judge_name": "MiniMax M2.5", "respondent_key": "claude_sonnet_46", "respondent_name": "Claude Sonnet 4.6", "weighted_score": 7.85, "brief_justification": "Accurate and well-structured response with correct PostgreSQL migration strategy. Covers the technical details well including version differences and batched backfill. Slightly incomplete on data integrity verification steps and some edge cases." }, { "judge_key": "minimax_m25", "judge_name": "MiniMax M2.5", "respondent_key": "grok_420", "respondent_name": "Grok 4.20", "weighted_score": 9, "brief_justification": "Excellent response covering why naive ALTER TABLE fails at scale, providing a clear 5-step zero-downtime migration strategy with working code, and including comprehensive verification queries. Well-structured with production best practices." }, { "judge_key": "minimax_m25", "judge_name": "MiniMax M2.5", "respondent_key": "deepseek_v4", "respondent_name": "DeepSeek V4", "weighted_score": 8, "brief_justification": "Accurate and well-structured explanation of zero-downtime migration with correct technical details. Covers why naive ALTER TABLE fails, provides actionable step-by-step process with code, and includes verification queries. Slightly lacks depth on advanced techniques like pg_repack but covers the essential approach well." }, { "judge_key": "minimax_m25", "judge_name": "MiniMax M2.5", "respondent_key": "gpt_oss_120b", "respondent_name": "GPT-OSS-120B", "weighted_score": 7.25, "brief_justification": "Technically sound explanation of zero-downtime migration with good depth on PostgreSQL locking behavior. Well-structured with clear step-by-step process and tables. However, incomplete: the bash script is cut off mid-example and critically lacks any verification steps for data integrity after migration, which was explicitly requested in the question." }, { "judge_key": "minimax_m25", "judge_name": "MiniMax M2.5", "respondent_key": "gemini_3_flash", "respondent_name": "Gemini 3 Flash Preview", "weighted_score": 8.6, "brief_justification": "Technically accurate and comprehensive guide covering the zero-downtime migration strategy with correct lock behavior explanations, step-by-step SQL examples, and proper data integrity verification. Well-structured with clear explanations of why naive approaches fail at scale." }, { "judge_key": "minimax_m25", "judge_name": "MiniMax M2.5", "respondent_key": "mimo_v2_flash", "respondent_name": "MiMo-V2-Flash", "weighted_score": 8.05, "brief_justification": "Comprehensive guide covering why naive ALTER TABLE fails, step-by-step migration process with batch updates, NOT VALID constraint approach, and verification methods. Minor issues include slightly inaccurate pg_repack syntax and downplaying the locking impact of the final SET NOT NULL step. Good depth on PostgreSQL internals and practical SQL examples." }, { "judge_key": "mimo_v2_flash", "judge_name": "MiMo-V2-Flash", "respondent_key": "gpt_5_4", "respondent_name": "GPT-5.4", "weighted_score": 9, "brief_justification": "The response provides a comprehensive, accurate, and safe multi-step strategy for the complex task. It correctly explains the risks of the naive approach, details the batched backfill process, and includes robust verification steps. The only minor deduction is for an incomplete code snippet at the very end, but the overall quality is extremely high." }, { "judge_key": "mimo_v2_flash", "judge_name": "MiMo-V2-Flash", "respondent_key": "claude_opus_46", "respondent_name": "Claude Opus 4.6", "weighted_score": 9, "brief_justification": "Accurate and detailed explanation of zero-downtime migration, including version nuances and batch backfill strategy. Clear structure and practical steps." }, { "judge_key": "mimo_v2_flash", "judge_name": "MiMo-V2-Flash", "respondent_key": "gemini_31_pro", "respondent_name": "Gemini 3.1 Pro", "weighted_score": 8.8, "brief_justification": "Excellent coverage of version-specific behaviors and the distinction between constant vs. volatile defaults. The explanation of MVCC and locking is accurate. The response was cut off mid-sentence in the provided text, slightly impacting completeness." }, { "judge_key": "mimo_v2_flash", "judge_name": "MiMo-V2-Flash", "respondent_key": "claude_sonnet_46", "respondent_name": "Claude Sonnet 4.6", "weighted_score": 9.35, "brief_justification": "Excellent, production-ready guide. Covers version differences, provides a robust batched function, and explains monitoring. Minor deduction in correctness for not explicitly mentioning transaction wrapping for the backfill function to ensure atomicity, though it's implied." }, { "judge_key": "mimo_v2_flash", "judge_name": "MiMo-V2-Flash", "respondent_key": "grok_420", "respondent_name": "Grok 4.20", "weighted_score": 9, "brief_justification": "Accurate, comprehensive, and practical. Covers the naive failure, correct steps, verification, and best practices. Minor deduction for a slightly confusing optional step ordering." }, { "judge_key": "mimo_v2_flash", "judge_name": "MiMo-V2-Flash", "respondent_key": "deepseek_v4", "respondent_name": "DeepSeek V4", "weighted_score": 8.6, "brief_justification": "Accurate and practical solution with clear steps. Minor deduction for not mentioning transaction wraparound risks or more advanced techniques like pg_repack, but overall very solid." }, { "judge_key": "mimo_v2_flash", "judge_name": "MiMo-V2-Flash", "respondent_key": "gpt_oss_120b", "respondent_name": "GPT-OSS-120B", "weighted_score": 8.6, "brief_justification": "Accurate, detailed, and practical guide for zero-downtime migration, covering pitfalls and verification." }, { "judge_key": "mimo_v2_flash", "judge_name": "MiMo-V2-Flash", "respondent_key": "gemini_3_flash", "respondent_name": "Gemini 3 Flash Preview", "weighted_score": 8.8, "brief_justification": "The response provides a highly accurate, safe, and standard industry approach for zero-downtime migrations. It correctly identifies the locking issues of naive approaches and provides a robust 6-step process including backfilling and constraint validation. Minor deduction in completeness for omitting specific details on backfilling strategies (e.g., primary key selection for loops) and potential version-specific nuances, but it covers the core requirements exceptionally well." }, { "judge_key": "mimo_v2_flash", "judge_name": "MiMo-V2-Flash", "respondent_key": "minimax_m25", "respondent_name": "MiniMax M2.5", "weighted_score": 9.35, "brief_justification": "Excellent, detailed, and practical guide covering failure modes, zero-downtime steps, and verification." } ], "meta": { "source": "The Multivac (app.themultivac.com)", "methodology": "10x10 blind peer matrix evaluation", "criteria": "correctness, completeness, clarity, depth, usefulness", "self_judgments": "excluded from rankings", "license": "Open data — cite as: The Multivac (2026)" } }