Backport/stable 25.8/92588 - #2254
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… concurrent in-place mutations ColumnNullable::shrinkToFit() now also shrinks the null-map column wrapper, and MergeTreeReadTask::read() uses IColumn::mutate() instead of a use_count()==1 check before shrinking, cloning shared subcolumns first to avoid a double-free/UAF when shrinkToFit() runs concurrently on a shared column. The MergeTreeRangeReader.cpp hunk from the upstream PR is not included: this branch has no canInplaceFilter()/assumeMutable()->filter() fast path, so that particular crash vector doesn't exist here.
…ToFit crash Adds 03681_mergetree_shrink_const_nested_nullable, targeting the case where a constant inside PREWHERE, wrapped in materialize(toNullable(materialize(...))), produces a ColumnNullable with use_count() == 1 at the top level but a shared nested column underneath -- the case the old use_count()==1 guard in MergeTreeReadTask::read() missed. Verified: reverting the ClickHouse#92588 backport fix reproduces a SIGSEGV in jemalloc (eset_remove/extent_recycle) within seconds of running this test; with the fix in place, the test passes reliably.
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Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):
Fix potential crash caused by in place mutation of underlying const PREWHERE columns. This could've happened at column shrinking (
IColumn::shrinkToFit) or filtering (IColumn::filter), which could've triggered concurrently from several threads. Backport of ClickHouse#92588.Documentation entry for user-facing changes
Fix potential crash caused by in place mutation of underlying const PREWHERE columns. This could've happened at column shrinking (
IColumn::shrinkToFit) or filtering (IColumn::filter), which could've triggered concurrently from several threads. Backport of ClickHouse#92588.CI/CD Options
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