Improve logic for reading dictionaries during row group pruning#14247
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raunaqmorarka merged 5 commits intotrinodb:masterfrom Sep 24, 2022
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Improve logic for reading dictionaries during row group pruning#14247raunaqmorarka merged 5 commits intotrinodb:masterfrom
raunaqmorarka merged 5 commits intotrinodb:masterfrom
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When the nulls count in column statistics for a column is 0, we can use that for setting nullAllowed to false in parquet dictionary domains
skrzypo987
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Sep 22, 2022
lib/trino-parquet/src/main/java/io/trino/parquet/predicate/Predicate.java
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lib/trino-parquet/src/main/java/io/trino/parquet/predicate/TupleDomainParquetPredicate.java
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Perform column index and dictionary lookups only for the subset of columns where it can be useful. This prevents unnecessary filesystem reads and decoding work when the predicate on a column comes from a connector's file-level min/max stats or more generally when the predicate selects a domain equal to or wider than row-group min/max.
Limits the size of the filesystem read to only the required length when fetching dictionary for row-group pruning in parquet
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sopel39
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Sep 23, 2022
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Do you think we should introduce feature flag for optimized reader first?
| @@ -21,11 +21,13 @@ | |||
| public class DictionaryDescriptor | |||
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When the nulls count in column statistics for a column is 0
Do you think it's possible for some writer to set it incorrectly?
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If column statistics are incorrect then our existing predicate pushdown logic could also give wrong results, so we should be able to rely on it
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These are targeted fixes/improvements in existing code and not a rewrite of the reader, so these shouldn't need to be behind a flag |
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Description
Improve logic for reading dictionaries during row group pruning in parquet reader
Non-technical explanation
Improves parquet reader performance in the presence of predicates.
Release notes
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