Query perf tuning: improve GroupBy query perf by setting initial size for HashMap #5291
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xiangfu0
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kishoreg,
Jackie-Jiang,
npawar,
jackjlli and
mcvsubbu
…hMap used in DictionaryBasedGroupKeyGenerator.
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May 20, 2020
For the use cases with high qps with low selectivity queries, initializing the hashmap with the size of the upperbound incurred more penalty as opposed to improving performance by reducing the number of hashmap resizes.
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Hashmap used in DictionaryBasedGroupKeyGenerator for holding groupKeys is initialized with default initial size(16), which is very small. This caused performance degradation for group by queries with many groupKeys.
In order to run select group by query, the time used to scan 36MM entries are:
Credit to @npawar , @kishoreg for benchmark