XDB reports unbiased estimators and confidence intervals periodically for an aggregation query. The confidence interval shrinks over time. The true result Y is within the confidence interval with high confidence.
Online aggregation queries are written in SQL with a few additional keywords. The example query finds the total revenue loss due to returned goods in a TPC-H dataset. The online aggregation query will be run for 60000 milliseconds and results are reported every 1000 milliseconds. The confidence interval is computed with confidence of 95%.
Online aggregation queries can be issued in a PSQL frontend and the results are reported at the end of the queries.
We also have a modified Apache Zeppelin frontend, which allows users to launch online aggregation queries in a web frontend and see the improvement of the results as the query is being executed.