Fix Block structure mismatch exception in UnionStep with PREWHERE and projections#99515
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alexey-milovidov merged 3 commits intomasterfrom Mar 23, 2026
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…nd projections Move the debug assertion in `UnionStep::updatePipeline` after the header conversion code. Previously, the assertion fired before the existing converting transform could fix the mismatch, causing a fatal error in debug/sanitizer builds. The mismatch occurs when PREWHERE optimization adds extra pass-through columns to `ReadFromMergeTree` output via `ActionsDAG::updateHeader` that are not consumed by the expression DAG above. This causes plan headers and actual pipeline headers to diverge. The conversion code already handles this gracefully by adding converting transforms, but the assertion prevented it from running in debug builds. Fixes #96131 https://s3.amazonaws.com/clickhouse-test-reports/json.html?REF=master&sha=73f45b0717e3a4763b7d1cde71950a076b5b00c7&name_0=MasterCI&name_1=Stress%20test%20%28azure%2C%20amd_msan%29 Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Workflow [PR], commit [21e09b2] Summary: ✅ AI ReviewSummaryThis PR fixes a debug/ASan-only ClickHouse Rules
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…WHERE and projections This test exercises the PREWHERE + projection + `query_plan_remove_unused_columns = 0` path that caused a debug assertion failure in `UnionStep::updatePipeline`. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Ok. Fairly minimal change.
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The EXPLAIN-based plan check for consecutive Expression steps was unreliable: it returned the same result on both the master binary (without the plan-level fix) and the patched binary because other plan optimizations also create consecutive Expression steps. The actual runtime fix for the `Block structure mismatch in UnionStep` exception was merged via PR #99515, which moved the debug assertion in `UnionStep::updatePipeline` after the header conversion code. This PR's plan-level fix in `optimizeUseNormalProjections` is a defense-in-depth measure that prevents the header mismatch from reaching the pipeline build stage. Keep only the query correctness check as a regression test. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
alexey-milovidov
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The bugfix validation test was failing because the query-success check alone cannot distinguish between master and this PR — PR #99515 already handles the header mismatch at pipeline level, so the query succeeds on both. Add a `setStepDescription` call to the converting `ExpressionStep` in `optimizeUseNormalProjections` so it appears as "Convert projection output to match expected header" in EXPLAIN output. The test now checks for this specific step description, which is absent on master and present with this fix. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
UnionStep" exception in debug/sanitizer buildsUnionStep::updatePipelinefired before the existing header conversion code could fix the mismatch, causing a fatal errorReadFromMergeTreeoutput viaActionsDAG::updateHeaderthat are not consumed by the expression DAG above, causing plan headers and pipeline headers to divergeTriggered by test
03722_normal_projection_key_columns.sqlwith parallel replicas +query_plan_remove_unused_columns = 0(stress test settings).Fixes #96131
CI report: https://s3.amazonaws.com/clickhouse-test-reports/json.html?REF=master&sha=73f45b0717e3a4763b7d1cde71950a076b5b00c7&name_0=MasterCI&name_1=Stress%20test%20%28azure%2C%20amd_msan%29
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