Add PercentileSmartTDigestAggregationFunction #8565
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Jackie-Jiang
added
feature
release-notes
xiangfu0
approved these changes
Apr 19, 2022
| ExpressionContext firstArgument = arguments.get(0); | ||
| if (upperCaseFunctionName.startsWith("PERCENTILE")) { | ||
| String remainingFunctionName = upperCaseFunctionName.substring(10); | ||
| if (remainingFunctionName.equals("SMARTTDIGEST")) { |
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case ignore match ?
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It's already canonicalized, so no need to ignore case
| public void aggregate(int length, AggregationResultHolder aggregationResultHolder, | ||
| Map<ExpressionContext, BlockValSet> blockValSetMap) { | ||
| BlockValSet blockValSet = blockValSetMap.get(_expression); | ||
| validateValueType(blockValSet); |
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Doing this once (upon first call to aggregate) should be enough ?
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Yes, but because the aggregation function itself is stateless (shared across threads), we cannot add a variable to the function to track if it is the first call. The overhead of this call should be minimal. Once we enforce schema, we should be able to perform all these checks on the broker side
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Description
Adds
PercentileSmartTDigestAggregationFunctionwhich can automatically convert theDoubleArrayListtoTDigestif the list size grows too big to protect the servers from running out of memory. This conversion only applies to aggregation only queries, but not the group-by queries.By default, when the list size exceeds 100K, it will be converted to a TDigest with compression of 100.
The threshold and compression can be configured using the third argument (literal) of the function:
threshold: list size threshold to trigger the conversion, non-positive means never convert (default 100K)compression: compression of the converted TDigest (default 100)Example query:
SELECT PERCENTILE_SMART_TDIGEST(myCol, 95, 'threshold=10;compression=50') FROM myTableRelease Notes
Adds
PercentileSmartTDigestAggregationFunctionwhich automatically stores values in DoubleArrayList or TDigest based on the number of values