DRILL-1328: Support table statistics - Part 2 Add support for avg row-width and major type statistics. Parallelize the ANALYZE implementation and stats UDF implementation to improve stats collection performance. Update/fix rowcount, selectivity and ndv computations to improve plan costing. Add options for configuring collection/usage of statistics. Add new APIs and implementation for stats writer (as a precursor to Drill Metastore APIs). Fix several stats/costing related issues identified while running TPC-H nad TPC-DS queries. Add support for CPU sampling and nested scalar columns. Add more testcases for collection and usage of statistics and fix remaining unit/functional test failures.
Thanks to Venki Korukanti (@vkorukanti) for the description below (modified to account for new changes). He graciously agreed to rebase the patch to latest master, fixed few issues and added few tests.
FUNCS: Statistics functions as UDFs: Separate Currently using FieldReader to ensure consistent output type so that Unpivot doesn't get confused. All stats columns should be Nullable, so that stats functions can return NULL when N/A. * custom versions of "count" that always return BigInt * HyperLogLog based NDV that returns BigInt that works only on VarChars * HyperLogLog with binary output that only works on VarChars
USAGE: Add getDrillTable() to DrillScanRelBase and ScanPrel * since ScanPrel does not inherit from DrillScanRelBase, this requires adding a DrillTable to the constructor * This is done so that a custom ReflectiveRelMetadataProvider can access the DrillTable associated with Logical/Physical scans.
USAGE: Attach DrillStatsTable to DrillTable. * DrillStatsTable represents the data scanned from a corresponding ".stats.drill" table * In order to avoid doing query execution right after the ".stats.drill" table is found, metadata is not actually collected until the MaterializationVisitor is used. ** Currently, the metadata source must be a string (so that a SQL query can be created). Doing this with a table is probably more complicated. ** Query is set up to extract only the most recent statistics results for each column.