perf(sql): optimize count_distinct symbol function#3974
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bluestreak01 merged 6 commits intomasterfrom Nov 20, 2023
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puzpuzpuz
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Includes the following optimizations: * Replaces CompactIntHashSet with BitSet in CountDistinctSymbolGroupByFunction. The former has a much more compact memory layout and faster operations. * Introduces early exit for SELECT count_distinct(sym_col) FROM my_table; queries. Exit condition is based on the symbol table size: as soon as it's reached, row iteration stops.
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@puzpuzpuz this is a very clever improvement 👍 how will it work with |
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If the filtered symbol values are only a subset of the full symbol table, the early exit check will be no-op (full loop over the base cursor). If all symbol values are returned by the filter, the check will kick in and redundant iteration over the base cursor will stop. That's done only in the |
eugenels
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Nov 20, 2023
...ain/java/io/questdb/griffin/engine/functions/groupby/CountDistinctSymbolGroupByFunction.java
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core/src/main/java/io/questdb/griffin/engine/groupby/GroupByNotKeyedRecordCursorFactory.java
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eugenels
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Nov 20, 2023
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[PR Coverage check]😍 pass : 68 / 71 (95.77%) file detail
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eugenels
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@eugenels thanks for the review! |
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Includes the following optimizations:
CompactIntHashSetwithBitSetinCountDistinctSymbolGroupByFunction. The former has a much more compact memory layout and faster operations.count_distinct()over symbol columns, e.g.SELECT count_distinct(sym_col) FROM my_table;. The exit condition is based on the symbol table sizes: as soon as they're reached, row iteration stops.