gianm commented on a change in pull request #10318:
URL: https://github.com/apache/druid/pull/10318#discussion_r477580012
##########
File path: processing/src/main/java/org/apache/druid/query/UnionQueryRunner.java
##########
@@ -41,34 +44,51 @@ public UnionQueryRunner(
public Sequence<T> run(final QueryPlus<T> queryPlus, final ResponseContext
responseContext)
{
Query<T> query = queryPlus.getQuery();
- DataSource dataSource = query.getDataSource();
- if (dataSource instanceof UnionDataSource) {
- return new MergeSequence<>(
- query.getResultOrdering(),
- Sequences.simple(
- Lists.transform(
- ((UnionDataSource) dataSource).getDataSources(),
- new Function<DataSource, Sequence<T>>()
- {
- @Override
- public Sequence<T> apply(DataSource singleSource)
- {
- return baseRunner.run(
- queryPlus.withQuery(
- query.withDataSource(singleSource)
- // assign the subqueryId. this will be used
to validate that every query servers
- // have responded per subquery in
RetryQueryRunner
- .withDefaultSubQueryId()
- ),
- responseContext
- );
- }
- }
- )
- )
- );
+ final DataSourceAnalysis analysis =
DataSourceAnalysis.forDataSource(query.getDataSource());
+
+ if (analysis.isConcreteTableBased() &&
analysis.getBaseUnionDataSource().isPresent()) {
+ // Union of tables.
+
+ final UnionDataSource unionDataSource =
analysis.getBaseUnionDataSource().get();
+
+ if (unionDataSource.getDataSources().isEmpty()) {
+ // Shouldn't happen, because UnionDataSource doesn't allow empty
unions.
+ throw new ISE("Unexpectedly received empty union");
+ } else if (unionDataSource.getDataSources().size() == 1) {
Review comment:
Yeah, the idea is let's not create a MergeSequence if there's only going
to be 1 thing.
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