gianm commented on code in PR #19726:
URL: https://github.com/apache/druid/pull/19726#discussion_r3636519918
##########
processing/src/main/java/org/apache/druid/segment/QueryableIndexCursorFactory.java:
##########
@@ -251,6 +286,19 @@ private CursorHolder makeMultiGroupClusteredCursorHolder(
);
}
+ // Time-ordered merge path: when the query asks for __time ordering AND
__time is the first non-clustering column
+ // (so each group, whose clustering prefix is constant, is individually
__time-sorted), present a globally
+ // __time-ordered cursor via a k-way merge across the groups instead of
the (clustering-first) concatenation. The
+ // per-group build spec carries the query's preferred ordering through
rebuildCursorBuildSpec, so each group cursor
+ // independently honors the requested direction (ascending, or descending
via a reversed offset).
Review Comment:
IMO a comment is not needed. The code is self-explanatory, and will be even
more so if the remainder of the method is moved to
`makeConcatenatedClusteredCursorHolder`. If you want a comment, try:
```java
// Use k-way merged group cursors for time ordering, or concatenated cursors
otherwise.
```
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