feat(partition-ttl): Introduce KeepByEventTimeStrategy to expire partitions by event time

Author: wangxianghu

hudi-client/hudi-client-common/src/main/java/org/apache/hudi/table/action/ttl/strategy/KeepByEventTimeStrategy.java

@@ -39,9 +39,8 @@
  * (last commit time) and {@link KeepByCreationTimeStrategy} (creation commit time).
  *
  * <h3>Supported path shapes</h3>
- * The first-class, tested shapes are day and hour granularity, configured via
- * {@link org.apache.hudi.config.HoodieTTLConfig#EVENT_TIME_FORMAT}. Each example shows the
- * partition path on the left and the required {@code startIndex} on the right (see
+ * The first-class, tested shapes are day and hour granularity. Each example shows the partition
+ * path on the left and the required {@code startIndex} on the right (see
  * <i>Locating the time block</i> below); non-time segments may appear before and/or after the
  * time block.
  * <ul>
@@ -90,16 +89,31 @@
  *
  * <h3>Locating the time block</h3>
  * The time block must occupy a <i>contiguous</i> segment range of the partition path. Only the
- * segments before it count toward
- * {@link org.apache.hudi.config.HoodieTTLConfig#EVENT_TIME_PARTITION_START_INDEX}; segments after
- * are ignored. Interleaved layouts such as {@code dt=20260627/source=app/hh=12} are not
- * supported -- the time block must be in one piece.
+ * segments before it count toward {@code startIndex}; segments after are ignored. Interleaved
+ * layouts such as {@code dt=20260627/source=app/hh=12} are not supported -- the time block must
+ * be in one piece.
  *
  * <h3>Time zone</h3>
  * Both the partition's event time and the cutoff derived from {@code instantTime} are interpreted
  * in UTC. Set {@code hoodie.table.timeline.timezone=UTC} so the timeline writes instants under the
  * same convention; otherwise the cutoff drifts by the JVM's UTC offset -- a boundary effect at
  * day granularity, a full-offset shift at hour granularity.
+ *
+ * <h3>Configuration</h3>
+ * All three knobs come with defaults, so a table whose partition path is purely a date in
+ * {@code yyyy-MM-dd} form works out of the box.
+ * <ul>
+ *   <li>{@link org.apache.hudi.config.HoodieTTLConfig#EVENT_TIME_FORMAT} — date-time pattern of
+ *       the time block in the partition path. Default {@code yyyy-MM-dd}. A {@code /} in the
+ *       pattern means the time block spans that many consecutive segments.</li>
+ *   <li>{@link org.apache.hudi.config.HoodieTTLConfig#EVENT_TIME_PARTITION_START_INDEX} —
+ *       0-based index of the first segment that carries the time block. Default {@code 0}.
+ *       Raise it when non-time segments come before the time block (see examples above).</li>
+ *   <li>{@link org.apache.hudi.config.HoodieTTLConfig#EVENT_TIME_DELETE_HIVE_DEFAULT_PARTITION} —
+ *       whether to treat partitions containing {@code __HIVE_DEFAULT_PARTITION__} (i.e. data
+ *       whose event-time column was {@code NULL}) as expired. Default {@code false}, i.e. such
+ *       partitions are skipped with a WARN and the user keeps explicit control over them.</li>
+ * </ul>
  */
 @Slf4j
 public class KeepByEventTimeStrategy extends KeepByTimeStrategy {