Prune parquet row groups using fully dictionary-encoded columns#23851
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DarkWanderer wants to merge 4 commits into
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Prune parquet row groups using fully dictionary-encoded columns#23851DarkWanderer wants to merge 4 commits into
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Adds an opt-in `dictionary_filter_on_read` config option (default false) that uses a fully dictionary-encoded BYTE_ARRAY (Utf8/Binary) column chunk's dictionary as an exact row-group membership index. Unlike the existing bloom-filter pruning stage, this is exact rather than probabilistic, so it can prune both `IN`/`=` (value absent) and `NOT IN`/`!=` (value is the chunk's only value) predicates. A column chunk is only used if its page encoding stats prove every data page came from the dictionary (`PLAIN_DICTIONARY` or `RLE_DICTIONARY` only) -- chunks that fell back to `PLAIN` encoding partway through are ignored, since a writer's dictionary fallback means the dictionary is no longer the complete value set. This depends on a new arrow-rs API to decode a dictionary page independent of the row-by-row array reader (arrow-rs#9010), not yet released; see the following commit for the temporary patch.
…anch Switches the [patch.crates-io] block from a local filesystem path to https://github.com/DarkWanderer/arrow-rs/tree/get-dictionary, so the build is reproducible for anyone (including CI) rather than only on one machine. Still temporary -- to be removed once arrow-rs releases a version with the dictionary decode API and the dependency is bumped normally.
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Thank you for opening this pull request! Reviewer note: cargo-semver-checks reported the current version number is not SemVer-compatible with the changes in this pull request (compared against the base branch). Details |
row_groups_pruned_dictionary was sorted after the page-index metrics in EXPLAIN output; group it with the other row-group-level pruning metrics (statistics, bloom filter) instead, and update the golden sqllogictest output accordingly. Also update the temporary Cargo.toml patch comment to point at arrow-rs PR apache#10420, which supersedes the now-closed apache#9011. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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## main #23851 +/- ##
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- Coverage 80.75% 80.71% -0.04%
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Branches 368809 369903 +1094
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Which issue does this PR close?
N/A
Rationale for this change
Dictionary pages are essentially free, exact indexes for
IN/NOT INqueries. Bloom filters can prove a target value is absent from a row group (useful for pruning=/IN), but they are probabilistic (non-zero false-positive rate) and cannot prove aNOT IN/!=exclusion, since that would require confirming every distinct value in the row group is excluded -- information a bloom filter doesn't retain. A fully dictionary-encoded column chunk does retain the complete set of distinct values, so it can prune exactly in both directions:IN/=when the dictionary is disjoint from the target set, andNOT IN/!=when the dictionary is a subset of the excluded set. This approach stacks with bloom filters: dictionary pruning subsumes bloom-filter pruning where it applies, and is exact (no false positives) where bloom filters are only probabilistic.What changes are included in this PR?
datafusion.execution.parquet.dictionary_filter_on_readconfig option (default
false).DictionaryStatistics(dictionary_filter.rs): an exactPruningStatisticsimpl backed by decoded dictionary values, plusis_fully_dictionary_encoded, which gates use of a chunk'sdictionary on its page encoding stats being exactly
PLAIN_DICTIONARY/RLE_DICTIONARY(a writer that fell back toPLAINpartway through no longer has a complete dictionary).RowGroupAccessPlanFilter::prune_by_dictionaryand aLoadDictionaries/PruneWithDictionariesstage in the Parquetopener's state machine, mirroring the existing bloom-filter stage.
row_groups_pruned_dictionarymetric,.sltcoverage(
parquet_dictionary_pruning.slt, plus the metric added to existingEXPLAIN ANALYZEgolden files), and a criterion benchmark comparingstatistics-only vs. bloom-filter vs. dictionary pruning.
This depends on a new arrow-rs API to decode a Parquet dictionary page: apache/arrow-rs#10420
(apache/arrow-rs#9010).
Temporary
[patch.crates-io]commit in PR exists to cover thatAre these changes tested?
Yes: unit tests in
dictionary_filter.rsmirroringbloom_filter.rs(absent value,
INlist absent, present value,!=sole value,NOT INlist, and a PLAIN-fallback chunk correctly not pruned), new.sltcoverage showingrow_groups_pruned_dictionaryinEXPLAIN ANALYZE, and a criterion benchmark.Are there any user-facing changes?
Yes: a new opt-in config option
dictionary_filter_on_read(defaultfalse, no behavior change unless enabled) and a newrow_groups_pruned_dictionarymetric inEXPLAIN ANALYZE.