Optimization of ORDER BY with respect to the ORDER key in MergeTree tables (continuation of #5042).#6054
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KochetovNicolai merged 59 commits intoClickHouse:masterfrom Jul 27, 2019
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…by, in case of complicated queries
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For changelog. Remove if this is non-significant change.
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Short description (up to few sentences):
Optimize queries with
ORDER BY expressionsclause, whereexpressionshave coinciding prefix withORDERkey inMergeTreetables.Detailed description (optional):
In these queries data now is read in order of order key. This allows to avoid reading all data in case of specified limit. Optimization works with both
ASCandDESCand doesn't work together withGROUP BYclause andFINALmodifier.Continuation of #5042.
TODO:
implement for processors.(will be implemented in separate task).