amansinha100 commented on a change in pull request #1718: DRILL-7121: Use
correct ndv when statistics is disabled
URL: https://github.com/apache/drill/pull/1718#discussion_r270054867
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File path:
exec/java-exec/src/main/java/org/apache/drill/exec/planner/cost/DrillRelMdDistinctRowCount.java
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@@ -75,8 +75,25 @@ public Double getDistinctRowCount(Join rel,
RelMetadataQuery mq,
@Override
public Double getDistinctRowCount(RelNode rel, RelMetadataQuery mq,
ImmutableBitSet groupKey, RexNode predicate) {
- if (rel instanceof TableScan && !DrillRelOptUtil.guessRows(rel)) {
- return getDistinctRowCount((TableScan) rel, mq, groupKey, predicate);
+ if (rel instanceof DrillScanRelBase) {
+ DrillTable table = rel.getTable().unwrap(DrillTable.class);
+ if (table == null) {
+ if (rel.getTable().unwrap(DrillTranslatableTable.class) != null) {
+ table =
rel.getTable().unwrap(DrillTranslatableTable.class).getDrillTable();
+ }
+ }
+ if (table != null && table.getStatsTable() != null &&
!DrillRelOptUtil.guessRows(rel)) {
+ return getDistinctRowCount(((DrillScanRelBase)rel), mq, table,
groupKey, rel.getRowType(), predicate);
+ } else {
+ // If guessing, return NDV as 0.1 * rowCount
+ /* If there is no table or metadata (stats) table associated with
scan, estimate the
+ * distinct row count. Consistent with the estimation of Aggregate row
count in
+ * RelMdRowCount: distinctRowCount = rowCount * 10%.
+ */
+ if (rel instanceof DrillScanRel) {
Review comment:
It would be good to add some comment here why the earlier check is for
DrillScanRelBase and this one is for DrillScanRel.
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