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Preserve original key order in bucketed Map serialization#109178
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Preserve original key order in bucketed Map serialization#109178Avogar wants to merge 3 commits into
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Bucketed Map serialization (PR #99200) splits map keys into buckets by hash, which reorders them. This breaks `ColumnMap::compareAt` (positional comparison) and operations that depend on it: ORDER BY, DISTINCT, GROUP BY, min/max, and equality filters on Map columns. Fix by writing an additional `MapBucketIndexes` substream during serialization that records each key-value pair's bucket index in original insertion order. During deserialization, this stream is used to reconstruct the original key order from per-bucket data. Key changes: - Add `SubstreamType::MapBucketIndexes` for the new stream - Add `CheckStreamExistsCallback` to `DeserializeBinaryBulkSettings` for backward compatibility with old parts lacking the stream - Update `SerializationMap`: write/read bucket indexes, implement `collectMapFromBucketsWithOrder` - Update `SerializationMapKeysOrValues`: same for `m.keys`/`m.values` subcolumn reads - Set `check_stream_exists_callback` in `MergeTreeReaderWide` and `MergeTreeReaderCompact` - Update existing test reference files for correct key ordering - Add stateless tests for key order preservation and comparison correctness - Add integration test for backward compatibility with old parts Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Bucketed Map serialization (PR #99200) splits map keys into buckets by hash, which reorders them. This breaks
ColumnMap::compareAt(positional comparison) and operations that depend on it:ORDER BY, DISTINCT, GROUP BY, min/max, and equality filters onMapcolumns.Fix by writing an additional
MapBucketIndexessubstream during serialization that records each key-value pair's bucket index in original insertion order. During deserialization, this stream is used to reconstruct the original key order from per-bucket data.Key changes:
SubstreamType::MapBucketIndexesfor the new streamCheckStreamExistsCallbacktoDeserializeBinaryBulkSettingsfor backward compatibility with old parts lacking the streamSerializationMap: write/read bucket indexes, implementcollectMapFromBucketsWithOrderSerializationMapKeysOrValues: same form.keys/m.valuessubcolumn readscheck_stream_exists_callbackinMergeTreeReaderWideandMergeTreeReaderCompactChangelog category (leave one):
Changelog entry (a user-readable short description of the changes that goes into CHANGELOG.md):
Preserve original key order in bucketed Map serialization to fix comparison operations that depend on it.