Hey, we are using presto on top of pinot. And we want to build star-tree index on the table. The aggregation function is DistinctCountHLL. And I will also use approx_distinct in prestoDB which is also back by HLL. I am wondering will presto respect this star-tree index in pinot?

From presto code I see it might be supported:

private String handleApproxDistinct(CallExpression aggregation, Map<VariableReferenceExpression, Selection> inputSelections)
        {
            List<RowExpression> inputs = aggregation.getArguments();
            if (inputs.isEmpty() || inputs.size() > 2) {
                throw new PinotException(PINOT_UNSUPPORTED_EXPRESSION, Optional.empty(), "Cannot handle approx_distinct function " + aggregation);
            }
            Selection selection = inputSelections.get(getVariableReference(inputs.get(0)));
            if (inputs.size() == 1) {
                return format("DISTINCTCOUNTHLL(%s)", selection);
            }
            RowExpression standardErrorInput = inputs.get(1);
            String standardErrorString;
            if (standardErrorInput instanceof ConstantExpression) {
                standardErrorString = getLiteralAsString((ConstantExpression) standardErrorInput);
            }

Try to use explain to see the query plan

I took the code snippet from https://github.com/prestodb/presto/blob/1e086105fdb0808316e72d15928d83eabe81be34/p[…]n/java/com/facebook/presto/pinot/query/PinotQueryGenerator.java

Yes, approx_distinct will be converted to distinctCounthll

Thank you guy! Sorry for the late reply. my company's vpn does not white list slack.