hudi-agent commented on code in PR #19081:
URL: https://github.com/apache/hudi/pull/19081#discussion_r3503112956


##########
hudi-client/hudi-client-common/src/main/java/org/apache/hudi/table/action/ttl/strategy/KeepByEventTimeStrategy.java:
##########
@@ -0,0 +1,292 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hudi.table.action.ttl.strategy;
+
+import org.apache.hudi.common.table.timeline.HoodieInstantTimeGenerator;
+import org.apache.hudi.common.util.PartitionPathEncodeUtils;
+import org.apache.hudi.table.HoodieTable;
+
+import lombok.extern.slf4j.Slf4j;
+
+import java.text.ParseException;
+import java.time.DateTimeException;
+import java.time.Instant;
+import java.time.LocalDate;
+import java.time.ZoneOffset;
+import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeParseException;
+import java.time.temporal.TemporalAccessor;
+import java.util.List;
+import java.util.stream.Collectors;
+
+/**
+ * Event-time based partition TTL strategy: lifetime is read from the 
partition path, not from
+ * commit metadata. Late-arriving writes into an old partition do not extend 
its lifetime, and
+ * backfilled historic partitions are still considered old. Compare with 
{@link KeepByTimeStrategy}
+ * (last commit time) and {@link KeepByCreationTimeStrategy} (creation commit 
time).
+ *
+ * <h3>Supported path shapes</h3>
+ * 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>
+ *   <li>Day, {@code format=yyyy-MM-dd}
+ *     <ul>
+ *       <li>time only: {@code 2026-06-27}, {@code dt=2026-06-27} — startIndex 
{@code 0}</li>
+ *       <li>prefix + time: {@code region=us/2026-06-27}, {@code 
region=us/dt=2026-06-27} — startIndex {@code 1}</li>
+ *       <li>time + suffix: {@code 2026-06-27/source=app}, {@code 
dt=2026-06-27/source=app} — startIndex {@code 0}</li>
+ *       <li>prefix + time + suffix: {@code 
region=us/dt=2026-06-27/source=app} — startIndex {@code 1}</li>
+ *     </ul>
+ *   </li>
+ *   <li>Day, {@code format=yyyyMMdd}
+ *     <ul>
+ *       <li>time only: {@code 20260627}, {@code dt=20260627} — startIndex 
{@code 0}</li>
+ *       <li>prefix + time: {@code region=us/20260627}, {@code 
region=us/dt=20260627} — startIndex {@code 1}</li>
+ *       <li>time + suffix: {@code 20260627/source=app}, {@code 
dt=20260627/source=app} — startIndex {@code 0}</li>
+ *       <li>prefix + time + suffix: {@code region=us/dt=20260627/source=app} 
— startIndex {@code 1}</li>
+ *     </ul>
+ *   </li>
+ *   <li>Hour, {@code format=yyyy-MM-dd/HH}
+ *     <ul>
+ *       <li>time only: {@code 2026-06-27/12}, {@code dt=2026-06-27/hh=12} — 
startIndex {@code 0}</li>
+ *       <li>prefix + time: {@code region=us/2026-06-27/12}, {@code 
region=us/dt=2026-06-27/hh=12} — startIndex {@code 1}</li>
+ *       <li>time + suffix: {@code 2026-06-27/12/source=app}, {@code 
dt=2026-06-27/hh=12/source=app} — startIndex {@code 0}</li>
+ *       <li>prefix + time + suffix: {@code 
region=us/dt=2026-06-27/hh=12/source=app} — startIndex {@code 1}</li>
+ *     </ul>
+ *   </li>
+ *   <li>Hour, {@code format=yyyyMMdd/HH}
+ *     <ul>
+ *       <li>time only: {@code 20260627/12}, {@code dt=20260627/hh=12} — 
startIndex {@code 0}</li>
+ *       <li>prefix + time: {@code region=us/20260627/12}, {@code 
region=us/dt=20260627/hh=12} — startIndex {@code 1}</li>
+ *       <li>time + suffix: {@code 20260627/12/source=app}, {@code 
dt=20260627/hh=12/source=app} — startIndex {@code 0}</li>
+ *       <li>prefix + time + suffix: {@code 
region=us/dt=20260627/hh=12/source=app} — startIndex {@code 1}</li>
+ *     </ul>
+ *   </li>
+ * </ul>
+ * Hive-style key names are not constrained: {@code dt=}, {@code day=}, {@code 
event_date=},
+ * {@code hh=}, {@code hour=} all work; only the value after {@code =} is 
parsed.
+ * <p>
+ * Any {@link java.time.format.DateTimeFormatter} pattern works as long as the 
resulting
+ * {@link java.time.temporal.TemporalAccessor} can be resolved to either an 
{@link java.time.Instant}
+ * or a {@link java.time.LocalDate} (day-only patterns are anchored at UTC 
start-of-day). A
+ * {@code /} in the pattern means the time value spans that many consecutive 
path segments.
+ * Patterns missing day-of-month, e.g. month-only {@code yyyy-MM}, cannot be 
resolved and will
+ * raise the standard parse-failure error at runtime.
+ *
+ * <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 {@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 whose time block contains {@code 
__HIVE_DEFAULT_PARTITION__}
+ *       in <i>any</i> segment as expired. Such a partition has an undefined 
event time (one of
+ *       its event-time columns was {@code NULL}, so the row cannot be placed 
on the configured
+ *       time axis) and falls outside the normal cutoff comparison. Default 
{@code false}, i.e.
+ *       such partitions are skipped with a WARN and the user keeps explicit 
control over them.
+ *       Applies to both single-segment formats (e.g. {@code 
dt=__HIVE_DEFAULT_PARTITION__}) and
+ *       multi-segment ones (e.g. {@code 
dt=2026-06-28/hh=__HIVE_DEFAULT_PARTITION__}).</li>
+ * </ul>
+ */
+@Slf4j
+public class KeepByEventTimeStrategy extends KeepByTimeStrategy {
+
+  private final String eventTimeFormat;
+  private final int startIndex;
+  private final boolean deleteHiveDefaultPartition;

Review Comment:
   🤖 nit: could you rename `startIndex` to `partitionStartIndex`? At the call 
site a few lines down it's the third positional argument in a 7-arg method 
call, and `startIndex` on its own doesn't tell the reader what it's indexing — 
`partitionStartIndex` (or `timeSegStartIndex`) would be self-explanatory there.
   
   <sub><i>⚠️ AI-generated; verify before applying. React 👍/👎 to flag 
quality.</i></sub>



##########
hudi-client/hudi-client-common/src/main/java/org/apache/hudi/config/HoodieWriteConfig.java:
##########
@@ -3058,6 +3058,23 @@ public Integer getPartitionTTLMaxPartitionsToDelete() {
     return getInt(HoodieTTLConfig.MAX_PARTITION_TO_DELETE);
   }
 
+  // The three event-time TTL getters all use *OrDefault flavors so the 
ConfigProperty defaults
+  // are honored even on paths that bypass HoodieTTLConfig.Builder (e.g. raw 
properties injected
+  // straight into HoodieWriteConfig without the builder's setDefaults pass).
+  // Note: getBoolean already short-circuits to getBooleanOrDefault when a 
default exists, so
+  // shouldDeleteHiveDefaultPartitionForEventTimeTTL keeps the plain call.
+  public String getPartitionTTLEventTimeFormat() {
+    return getStringOrDefault(HoodieTTLConfig.EVENT_TIME_FORMAT);
+  }
+
+  public int getPartitionTTLEventTimePartitionStartIndex() {
+    return getIntOrDefault(HoodieTTLConfig.EVENT_TIME_PARTITION_START_INDEX);
+  }
+
+  public boolean shouldDeleteHiveDefaultPartitionForEventTimeTTL() {
+    return 
getBoolean(HoodieTTLConfig.EVENT_TIME_DELETE_HIVE_DEFAULT_PARTITION);

Review Comment:
   🤖 nit: the block comment above this method exists solely to justify why 
`getBoolean` is used here instead of `getBooleanOrDefault` like the two 
adjacent getters. If the comment is correct that `getBoolean` already delegates 
to `getBooleanOrDefault` when a default exists, could you just use 
`getBooleanOrDefault` here too and drop the comment? All three getters would 
then read identically, and the asymmetry — along with its explanation — 
disappears.
   
   <sub><i>⚠️ AI-generated; verify before applying. React 👍/👎 to flag 
quality.</i></sub>



##########
hudi-client/hudi-client-common/src/main/java/org/apache/hudi/table/action/ttl/strategy/KeepByEventTimeStrategy.java:
##########
@@ -0,0 +1,275 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hudi.table.action.ttl.strategy;
+
+import org.apache.hudi.common.table.timeline.HoodieInstantTimeGenerator;
+import org.apache.hudi.common.util.PartitionPathEncodeUtils;
+import org.apache.hudi.table.HoodieTable;
+
+import lombok.extern.slf4j.Slf4j;
+
+import java.text.ParseException;
+import java.time.ZoneOffset;
+import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeParseException;
+import java.time.temporal.TemporalAccessor;
+import java.util.List;
+import java.util.stream.Collectors;
+
+/**
+ * Event-time based partition TTL strategy: lifetime is read from the 
partition path, not from
+ * commit metadata. Late-arriving writes into an old partition do not extend 
its lifetime, and
+ * backfilled historic partitions are still considered old. Compare with 
{@link KeepByTimeStrategy}
+ * (last commit time) and {@link KeepByCreationTimeStrategy} (creation commit 
time).
+ *
+ * <h3>Supported path shapes</h3>
+ * 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>
+ *   <li>Day, {@code format=yyyy-MM-dd}
+ *     <ul>
+ *       <li>time only: {@code 2026-06-27}, {@code dt=2026-06-27} — startIndex 
{@code 0}</li>
+ *       <li>prefix + time: {@code region=us/2026-06-27}, {@code 
region=us/dt=2026-06-27} — startIndex {@code 1}</li>
+ *       <li>time + suffix: {@code 2026-06-27/source=app}, {@code 
dt=2026-06-27/source=app} — startIndex {@code 0}</li>
+ *       <li>prefix + time + suffix: {@code 
region=us/dt=2026-06-27/source=app} — startIndex {@code 1}</li>
+ *     </ul>
+ *   </li>
+ *   <li>Day, {@code format=yyyyMMdd}
+ *     <ul>
+ *       <li>time only: {@code 20260627}, {@code dt=20260627} — startIndex 
{@code 0}</li>
+ *       <li>prefix + time: {@code region=us/20260627}, {@code 
region=us/dt=20260627} — startIndex {@code 1}</li>
+ *       <li>time + suffix: {@code 20260627/source=app}, {@code 
dt=20260627/source=app} — startIndex {@code 0}</li>
+ *       <li>prefix + time + suffix: {@code region=us/dt=20260627/source=app} 
— startIndex {@code 1}</li>
+ *     </ul>
+ *   </li>
+ *   <li>Hour, {@code format=yyyy-MM-dd/HH}
+ *     <ul>
+ *       <li>time only: {@code 2026-06-27/12}, {@code dt=2026-06-27/hh=12} — 
startIndex {@code 0}</li>
+ *       <li>prefix + time: {@code region=us/2026-06-27/12}, {@code 
region=us/dt=2026-06-27/hh=12} — startIndex {@code 1}</li>
+ *       <li>time + suffix: {@code 2026-06-27/12/source=app}, {@code 
dt=2026-06-27/hh=12/source=app} — startIndex {@code 0}</li>
+ *       <li>prefix + time + suffix: {@code 
region=us/dt=2026-06-27/hh=12/source=app} — startIndex {@code 1}</li>
+ *     </ul>
+ *   </li>
+ *   <li>Hour, {@code format=yyyyMMdd/HH}
+ *     <ul>
+ *       <li>time only: {@code 20260627/12}, {@code dt=20260627/hh=12} — 
startIndex {@code 0}</li>
+ *       <li>prefix + time: {@code region=us/20260627/12}, {@code 
region=us/dt=20260627/hh=12} — startIndex {@code 1}</li>
+ *       <li>time + suffix: {@code 20260627/12/source=app}, {@code 
dt=20260627/hh=12/source=app} — startIndex {@code 0}</li>
+ *       <li>prefix + time + suffix: {@code 
region=us/dt=20260627/hh=12/source=app} — startIndex {@code 1}</li>
+ *     </ul>
+ *   </li>
+ * </ul>
+ * Hive-style key names are not constrained: {@code dt=}, {@code day=}, {@code 
event_date=},
+ * {@code hh=}, {@code hour=} all work; only the value after {@code =} is 
parsed.
+ * <p>
+ * Any {@link java.time.format.DateTimeFormatter} pattern works as long as the 
resulting
+ * {@link java.time.temporal.TemporalAccessor} can be resolved to either an 
{@link java.time.Instant}
+ * or a {@link java.time.LocalDate} (day-only patterns are anchored at UTC 
start-of-day). A
+ * {@code /} in the pattern means the time value spans that many consecutive 
path segments.
+ * Patterns missing day-of-month, e.g. month-only {@code yyyy-MM}, cannot be 
resolved and will
+ * raise the standard parse-failure error at runtime.
+ *
+ * <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 {@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 {
+
+  private final String eventTimeFormat;
+  private final int startIndex;
+  private final boolean deleteHiveDefaultPartition;
+  private final boolean hiveStylePartitioning;
+
+  public KeepByEventTimeStrategy(HoodieTable hoodieTable, String instantTime) {
+    super(hoodieTable, instantTime);
+    // Defaults: format='yyyy-MM-dd', startIndex=0, 
deleteHiveDefaultPartition=false. The two
+    // guards below catch users who set the values explicitly to 
obviously-broken inputs.
+    this.eventTimeFormat = writeConfig.getPartitionTTLEventTimeFormat();
+    if (eventTimeFormat == null || eventTimeFormat.isEmpty()) {
+      throw new IllegalArgumentException(
+          "hoodie.partition.ttl.strategy.event.time.format must not be 
empty.");
+    }
+    this.startIndex = 
writeConfig.getPartitionTTLEventTimePartitionStartIndex();
+    if (startIndex < 0) {
+      throw new IllegalArgumentException(
+          "hoodie.partition.ttl.strategy.event.time.partition.start.index must 
be >= 0, got " + startIndex);
+    }
+    this.deleteHiveDefaultPartition = 
writeConfig.shouldDeleteHiveDefaultPartitionForEventTimeTTL();
+    // Hive-style partitioning is a table-level property recorded at table 
creation; trust it
+    // rather than guessing per-segment from a stray '=' character in a value.
+    this.hiveStylePartitioning = Boolean.parseBoolean(
+        
hoodieTable.getMetaClient().getTableConfig().getHiveStylePartitioningEnable());
+  }
+
+  @Override
+  protected List<String> getExpiredPartitionsForTimeStrategy(List<String> 
partitionPathsForTTL) {
+    long cutoffMillis = resolveCutoffMillis(instantTime, ttlInMilis);

Review Comment:
   🤖 This looks resolved in the current revision — `KeepByTimeStrategy` now 
computes `ttlInMilis = 
TimeUnit.DAYS.toMillis(getPartitionTTLStrategyDaysRetain())` (line 50), which 
widens to long before multiplying, so the 32-bit wrap at >=25 days is gone. 
`TestPartitionTTLStrategy` also adds boundary cases at 24/25/30/365 days, so 
the overflow path you flagged is now covered by a test.



##########
hudi-client/hudi-client-common/src/main/java/org/apache/hudi/table/action/ttl/strategy/KeepByEventTimeStrategy.java:
##########
@@ -0,0 +1,292 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hudi.table.action.ttl.strategy;
+
+import org.apache.hudi.common.table.timeline.HoodieInstantTimeGenerator;
+import org.apache.hudi.common.util.PartitionPathEncodeUtils;
+import org.apache.hudi.table.HoodieTable;
+
+import lombok.extern.slf4j.Slf4j;
+
+import java.text.ParseException;
+import java.time.DateTimeException;
+import java.time.Instant;
+import java.time.LocalDate;
+import java.time.ZoneOffset;
+import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeParseException;
+import java.time.temporal.TemporalAccessor;
+import java.util.List;
+import java.util.stream.Collectors;
+
+/**
+ * Event-time based partition TTL strategy: lifetime is read from the 
partition path, not from
+ * commit metadata. Late-arriving writes into an old partition do not extend 
its lifetime, and
+ * backfilled historic partitions are still considered old. Compare with 
{@link KeepByTimeStrategy}
+ * (last commit time) and {@link KeepByCreationTimeStrategy} (creation commit 
time).
+ *
+ * <h3>Supported path shapes</h3>
+ * 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>
+ *   <li>Day, {@code format=yyyy-MM-dd}
+ *     <ul>
+ *       <li>time only: {@code 2026-06-27}, {@code dt=2026-06-27} — startIndex 
{@code 0}</li>
+ *       <li>prefix + time: {@code region=us/2026-06-27}, {@code 
region=us/dt=2026-06-27} — startIndex {@code 1}</li>
+ *       <li>time + suffix: {@code 2026-06-27/source=app}, {@code 
dt=2026-06-27/source=app} — startIndex {@code 0}</li>
+ *       <li>prefix + time + suffix: {@code 
region=us/dt=2026-06-27/source=app} — startIndex {@code 1}</li>
+ *     </ul>
+ *   </li>
+ *   <li>Day, {@code format=yyyyMMdd}
+ *     <ul>
+ *       <li>time only: {@code 20260627}, {@code dt=20260627} — startIndex 
{@code 0}</li>
+ *       <li>prefix + time: {@code region=us/20260627}, {@code 
region=us/dt=20260627} — startIndex {@code 1}</li>
+ *       <li>time + suffix: {@code 20260627/source=app}, {@code 
dt=20260627/source=app} — startIndex {@code 0}</li>
+ *       <li>prefix + time + suffix: {@code region=us/dt=20260627/source=app} 
— startIndex {@code 1}</li>
+ *     </ul>
+ *   </li>
+ *   <li>Hour, {@code format=yyyy-MM-dd/HH}
+ *     <ul>
+ *       <li>time only: {@code 2026-06-27/12}, {@code dt=2026-06-27/hh=12} — 
startIndex {@code 0}</li>
+ *       <li>prefix + time: {@code region=us/2026-06-27/12}, {@code 
region=us/dt=2026-06-27/hh=12} — startIndex {@code 1}</li>
+ *       <li>time + suffix: {@code 2026-06-27/12/source=app}, {@code 
dt=2026-06-27/hh=12/source=app} — startIndex {@code 0}</li>
+ *       <li>prefix + time + suffix: {@code 
region=us/dt=2026-06-27/hh=12/source=app} — startIndex {@code 1}</li>
+ *     </ul>
+ *   </li>
+ *   <li>Hour, {@code format=yyyyMMdd/HH}
+ *     <ul>
+ *       <li>time only: {@code 20260627/12}, {@code dt=20260627/hh=12} — 
startIndex {@code 0}</li>
+ *       <li>prefix + time: {@code region=us/20260627/12}, {@code 
region=us/dt=20260627/hh=12} — startIndex {@code 1}</li>
+ *       <li>time + suffix: {@code 20260627/12/source=app}, {@code 
dt=20260627/hh=12/source=app} — startIndex {@code 0}</li>
+ *       <li>prefix + time + suffix: {@code 
region=us/dt=20260627/hh=12/source=app} — startIndex {@code 1}</li>
+ *     </ul>
+ *   </li>
+ * </ul>
+ * Hive-style key names are not constrained: {@code dt=}, {@code day=}, {@code 
event_date=},
+ * {@code hh=}, {@code hour=} all work; only the value after {@code =} is 
parsed.
+ * <p>
+ * Any {@link java.time.format.DateTimeFormatter} pattern works as long as the 
resulting
+ * {@link java.time.temporal.TemporalAccessor} can be resolved to either an 
{@link java.time.Instant}
+ * or a {@link java.time.LocalDate} (day-only patterns are anchored at UTC 
start-of-day). A
+ * {@code /} in the pattern means the time value spans that many consecutive 
path segments.
+ * Patterns missing day-of-month, e.g. month-only {@code yyyy-MM}, cannot be 
resolved and will
+ * raise the standard parse-failure error at runtime.
+ *
+ * <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 {@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 whose time block contains {@code 
__HIVE_DEFAULT_PARTITION__}
+ *       in <i>any</i> segment as expired. Such a partition has an undefined 
event time (one of
+ *       its event-time columns was {@code NULL}, so the row cannot be placed 
on the configured
+ *       time axis) and falls outside the normal cutoff comparison. Default 
{@code false}, i.e.
+ *       such partitions are skipped with a WARN and the user keeps explicit 
control over them.
+ *       Applies to both single-segment formats (e.g. {@code 
dt=__HIVE_DEFAULT_PARTITION__}) and
+ *       multi-segment ones (e.g. {@code 
dt=2026-06-28/hh=__HIVE_DEFAULT_PARTITION__}).</li>
+ * </ul>
+ */
+@Slf4j
+public class KeepByEventTimeStrategy extends KeepByTimeStrategy {
+
+  private final String eventTimeFormat;
+  private final int startIndex;
+  private final boolean deleteHiveDefaultPartition;
+  private final boolean hiveStylePartitioning;
+
+  public KeepByEventTimeStrategy(HoodieTable hoodieTable, String instantTime) {
+    super(hoodieTable, instantTime);
+    // Defaults: format='yyyy-MM-dd', startIndex=0, 
deleteHiveDefaultPartition=false. The two
+    // guards below catch users who set the values explicitly to 
obviously-broken inputs.
+    this.eventTimeFormat = writeConfig.getPartitionTTLEventTimeFormat();
+    if (eventTimeFormat == null || eventTimeFormat.isEmpty()) {
+      throw new IllegalArgumentException(
+          "hoodie.partition.ttl.strategy.event.time.format must not be 
empty.");
+    }
+    this.startIndex = 
writeConfig.getPartitionTTLEventTimePartitionStartIndex();
+    if (startIndex < 0) {
+      throw new IllegalArgumentException(
+          "hoodie.partition.ttl.strategy.event.time.partition.start.index must 
be >= 0, got " + startIndex);
+    }
+    this.deleteHiveDefaultPartition = 
writeConfig.shouldDeleteHiveDefaultPartitionForEventTimeTTL();
+    // Hive-style partitioning is a table-level property recorded at table 
creation; trust it
+    // rather than guessing per-segment from a stray '=' character in a value.
+    this.hiveStylePartitioning = Boolean.parseBoolean(
+        
hoodieTable.getMetaClient().getTableConfig().getHiveStylePartitioningEnable());
+  }
+
+  @Override
+  protected List<String> getExpiredPartitionsForTimeStrategy(List<String> 
partitionPathsForTTL) {
+    long cutoffMillis = resolveCutoffMillis(instantTime, ttlInMilis);
+    DateTimeFormatter formatter = 
DateTimeFormatter.ofPattern(eventTimeFormat).withZone(ZoneOffset.UTC);
+    int segCount = segmentCount(eventTimeFormat);
+    return partitionPathsForTTL.stream().parallel()
+        .filter(path -> isPartitionExpiredByEventTime(
+            path, formatter, startIndex, segCount, cutoffMillis, 
deleteHiveDefaultPartition, hiveStylePartitioning))
+        .collect(Collectors.toList());
+  }
+
+  /**
+   * Number of '/'-separated path segments the configured format occupies.
+   * Example: {@code yyyy-MM-dd/HH} -> 2.
+   */
+  static int segmentCount(String format) {
+    return format.split("/").length;
+  }
+
+  /**
+   * Resolve the "now" reference timestamp from {@code instantTime}, in UTC.
+   * <p>
+   * Anchoring on {@code instantTime} keeps the strategy idempotent across 
retries of the same
+   * replace commit. We parse it in UTC so the cutoff and the partition's 
event time (also parsed
+   * in UTC above) sit on the same axis -- otherwise expiry drifts by the 
JVM's UTC offset, which
+   * is negligible at day granularity but a full-offset shift at hour 
granularity.
+   */
+  static long resolveCutoffMillis(String instantTime, long ttlInMillis) {
+    try {
+      return HoodieInstantTimeGenerator.parseDateFromInstantTime(instantTime, 
ZoneOffset.UTC).getTime() - ttlInMillis;
+    } catch (ParseException e) {
+      throw new IllegalStateException("Failed to parse instant time " + 
instantTime, e);
+    }
+  }
+
+  /**
+   * Decide whether a partition path is expired.
+   * <p>
+   * The strategy treats any partition that cannot be parsed under the 
configured format /
+   * start-index / hive-style as a hard error. Reasoning: this class derives 
lifetime from the
+   * path itself, so a partition we cannot parse has no defined lifetime, and 
silently skipping
+   * it would leave it in the table forever while the rest of TTL appears to 
succeed. Switch to
+   * {@code KEEP_BY_TIME} or {@code KEEP_BY_CREATION_TIME} (which key off 
commit metadata, not
+   * the path) if the table contains partitions that don't conform to a single 
event-time shape.
+   * <p>
+   * Package-private so unit tests can exercise it directly without spinning 
up a HoodieTable.
+   */
+  static boolean isPartitionExpiredByEventTime(String partitionPath,
+                                               DateTimeFormatter formatter,
+                                               int startIndex,
+                                               int segCount,
+                                               long cutoffMillis,
+                                               boolean 
deleteHiveDefaultPartition,
+                                               boolean hiveStylePartitioning) {
+    String[] segments = partitionPath.split("/");
+    if (segments.length < startIndex + segCount) {
+      throw new IllegalArgumentException(String.format(
+          "Partition '%s' has %d segment(s) but the configured event time 
spans %d segment(s) starting at index %d. "
+              + "Check hoodie.partition.ttl.strategy.event.time.format and 
event.time.partition.start.index, "
+              + "or switch to KEEP_BY_TIME / KEEP_BY_CREATION_TIME if not all 
partitions of this table follow an event-time shape.",
+          partitionPath, segments.length, segCount, startIndex));
+    }
+
+    String[] timeSegs = new String[segCount];
+    boolean hasDefaultSegment = false;
+    for (int i = 0; i < segCount; i++) {
+      String seg = segments[startIndex + i];
+      if (hiveStylePartitioning) {
+        int eq = seg.indexOf('=');
+        if (eq < 0) {
+          throw new IllegalArgumentException(String.format(
+              "Partition '%s' segment '%s' has no hive-style 'field=value' 
prefix but "
+                  + "hoodie.datasource.write.hive_style_partitioning=true on 
the table. "
+                  + "Switch to KEEP_BY_TIME / KEEP_BY_CREATION_TIME if such 
legacy partitions must coexist.",
+              partitionPath, seg));
+        }
+        timeSegs[i] = seg.substring(eq + 1);
+      } else {
+        timeSegs[i] = seg;
+      }
+      if (PartitionPathEncodeUtils.DEFAULT_PARTITION_PATH.equals(timeSegs[i])) 
{
+        hasDefaultSegment = true;
+      }
+    }
+
+    // Any default-marker segment means the event time itself is undefined: a 
date-recorded /
+    // hour-NULL row cannot be placed on the hour axis any more than a 
date-NULL row can. We
+    // therefore treat the whole time block as "the default partition" and let 
the explicit
+    // user switch decide. Without this branch a multi-segment shape like
+    // dt=2026-06-28/hh=__HIVE_DEFAULT_PARTITION__ would either silently 
expire (old code) or
+    // stall TTL forever on a hard error.
+    if (hasDefaultSegment) {
+      if (deleteHiveDefaultPartition) {
+        log.info("Partition '{}' time block contains {} (event time undefined) 
and delete switch "
+            + "is on; marking expired", partitionPath, 
PartitionPathEncodeUtils.DEFAULT_PARTITION_PATH);
+        return true;
+      }
+      log.warn("Skipping partition '{}': time block contains {} (event time 
undefined; set "
+              + 
"hoodie.partition.ttl.strategy.event.time.delete.hive.default.partition=true to 
delete)",
+          partitionPath, PartitionPathEncodeUtils.DEFAULT_PARTITION_PATH);
+      return false;
+    }
+
+    String timeStr = String.join("/", timeSegs);
+    Long eventMillis = parseEventMillis(timeStr, formatter);
+    if (eventMillis == null) {
+      throw new IllegalArgumentException(String.format(
+          "Partition '%s': cannot parse '%s' with pattern '%s'. "
+              + "Fix hoodie.partition.ttl.strategy.event.time.format, or 
switch to "
+              + "KEEP_BY_TIME / KEEP_BY_CREATION_TIME if such partitions must 
remain in the table.",
+          partitionPath, timeStr, formatter));
+    }
+    return eventMillis < cutoffMillis;
+  }
+
+  /**
+   * Parse {@code timeStr} into epoch millis. Tries full date-time first; 
falls back to a
+   * date-only parse anchored at UTC start-of-day so day-level patterns (e.g. 
{@code yyyy-MM-dd})
+   * also work.
+   */
+  static Long parseEventMillis(String timeStr, DateTimeFormatter formatter) {
+    TemporalAccessor parsed;
+    try {
+      parsed = formatter.parse(timeStr);
+    } catch (DateTimeParseException e) {
+      return null;
+    }
+    try {
+      return Instant.from(parsed).toEpochMilli();

Review Comment:
   🤖 For zone-less patterns like `yyyy-MM-dd/HH`, `formatter.parse()` yields a 
`Parsed` with date+time+override-zone but no `INSTANT_SECONDS`, so 
`Instant.from(parsed)` throws and control falls to the 
`LocalDate.from(...).atStartOfDay()` branch below — dropping the hour (unlike 
`ZonedDateTime.from`, `Instant.from` has no `LocalDateTime` fallback). Could 
you double-check `hourBoundaryRespected` actually separates hh=11 from hh=12? I 
believe both currently resolve to start-of-day. Parsing via 
`LocalDateTime.from(parsed).atZone(ZoneOffset.UTC)` before the `LocalDate` 
fallback would preserve the hour.
   
   <sub><i>⚠️ AI-generated; verify before applying. React 👍/👎 to flag 
quality.</i></sub>



##########
hudi-client/hudi-client-common/src/main/java/org/apache/hudi/table/action/ttl/strategy/KeepByEventTimeStrategy.java:
##########
@@ -0,0 +1,275 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hudi.table.action.ttl.strategy;
+
+import org.apache.hudi.common.table.timeline.HoodieInstantTimeGenerator;
+import org.apache.hudi.common.util.PartitionPathEncodeUtils;
+import org.apache.hudi.table.HoodieTable;
+
+import lombok.extern.slf4j.Slf4j;
+
+import java.text.ParseException;
+import java.time.ZoneOffset;
+import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeParseException;
+import java.time.temporal.TemporalAccessor;
+import java.util.List;
+import java.util.stream.Collectors;
+
+/**
+ * Event-time based partition TTL strategy: lifetime is read from the 
partition path, not from
+ * commit metadata. Late-arriving writes into an old partition do not extend 
its lifetime, and
+ * backfilled historic partitions are still considered old. Compare with 
{@link KeepByTimeStrategy}
+ * (last commit time) and {@link KeepByCreationTimeStrategy} (creation commit 
time).
+ *
+ * <h3>Supported path shapes</h3>
+ * 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>
+ *   <li>Day, {@code format=yyyy-MM-dd}
+ *     <ul>
+ *       <li>time only: {@code 2026-06-27}, {@code dt=2026-06-27} — startIndex 
{@code 0}</li>
+ *       <li>prefix + time: {@code region=us/2026-06-27}, {@code 
region=us/dt=2026-06-27} — startIndex {@code 1}</li>
+ *       <li>time + suffix: {@code 2026-06-27/source=app}, {@code 
dt=2026-06-27/source=app} — startIndex {@code 0}</li>
+ *       <li>prefix + time + suffix: {@code 
region=us/dt=2026-06-27/source=app} — startIndex {@code 1}</li>
+ *     </ul>
+ *   </li>
+ *   <li>Day, {@code format=yyyyMMdd}
+ *     <ul>
+ *       <li>time only: {@code 20260627}, {@code dt=20260627} — startIndex 
{@code 0}</li>
+ *       <li>prefix + time: {@code region=us/20260627}, {@code 
region=us/dt=20260627} — startIndex {@code 1}</li>
+ *       <li>time + suffix: {@code 20260627/source=app}, {@code 
dt=20260627/source=app} — startIndex {@code 0}</li>
+ *       <li>prefix + time + suffix: {@code region=us/dt=20260627/source=app} 
— startIndex {@code 1}</li>
+ *     </ul>
+ *   </li>
+ *   <li>Hour, {@code format=yyyy-MM-dd/HH}
+ *     <ul>
+ *       <li>time only: {@code 2026-06-27/12}, {@code dt=2026-06-27/hh=12} — 
startIndex {@code 0}</li>
+ *       <li>prefix + time: {@code region=us/2026-06-27/12}, {@code 
region=us/dt=2026-06-27/hh=12} — startIndex {@code 1}</li>
+ *       <li>time + suffix: {@code 2026-06-27/12/source=app}, {@code 
dt=2026-06-27/hh=12/source=app} — startIndex {@code 0}</li>
+ *       <li>prefix + time + suffix: {@code 
region=us/dt=2026-06-27/hh=12/source=app} — startIndex {@code 1}</li>
+ *     </ul>
+ *   </li>
+ *   <li>Hour, {@code format=yyyyMMdd/HH}
+ *     <ul>
+ *       <li>time only: {@code 20260627/12}, {@code dt=20260627/hh=12} — 
startIndex {@code 0}</li>
+ *       <li>prefix + time: {@code region=us/20260627/12}, {@code 
region=us/dt=20260627/hh=12} — startIndex {@code 1}</li>
+ *       <li>time + suffix: {@code 20260627/12/source=app}, {@code 
dt=20260627/hh=12/source=app} — startIndex {@code 0}</li>
+ *       <li>prefix + time + suffix: {@code 
region=us/dt=20260627/hh=12/source=app} — startIndex {@code 1}</li>
+ *     </ul>
+ *   </li>
+ * </ul>
+ * Hive-style key names are not constrained: {@code dt=}, {@code day=}, {@code 
event_date=},
+ * {@code hh=}, {@code hour=} all work; only the value after {@code =} is 
parsed.
+ * <p>
+ * Any {@link java.time.format.DateTimeFormatter} pattern works as long as the 
resulting
+ * {@link java.time.temporal.TemporalAccessor} can be resolved to either an 
{@link java.time.Instant}
+ * or a {@link java.time.LocalDate} (day-only patterns are anchored at UTC 
start-of-day). A
+ * {@code /} in the pattern means the time value spans that many consecutive 
path segments.
+ * Patterns missing day-of-month, e.g. month-only {@code yyyy-MM}, cannot be 
resolved and will
+ * raise the standard parse-failure error at runtime.
+ *
+ * <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 {@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 {
+
+  private final String eventTimeFormat;
+  private final int startIndex;
+  private final boolean deleteHiveDefaultPartition;
+  private final boolean hiveStylePartitioning;
+
+  public KeepByEventTimeStrategy(HoodieTable hoodieTable, String instantTime) {
+    super(hoodieTable, instantTime);
+    // Defaults: format='yyyy-MM-dd', startIndex=0, 
deleteHiveDefaultPartition=false. The two
+    // guards below catch users who set the values explicitly to 
obviously-broken inputs.
+    this.eventTimeFormat = writeConfig.getPartitionTTLEventTimeFormat();
+    if (eventTimeFormat == null || eventTimeFormat.isEmpty()) {
+      throw new IllegalArgumentException(
+          "hoodie.partition.ttl.strategy.event.time.format must not be 
empty.");
+    }
+    this.startIndex = 
writeConfig.getPartitionTTLEventTimePartitionStartIndex();
+    if (startIndex < 0) {
+      throw new IllegalArgumentException(
+          "hoodie.partition.ttl.strategy.event.time.partition.start.index must 
be >= 0, got " + startIndex);
+    }
+    this.deleteHiveDefaultPartition = 
writeConfig.shouldDeleteHiveDefaultPartitionForEventTimeTTL();
+    // Hive-style partitioning is a table-level property recorded at table 
creation; trust it
+    // rather than guessing per-segment from a stray '=' character in a value.
+    this.hiveStylePartitioning = Boolean.parseBoolean(
+        
hoodieTable.getMetaClient().getTableConfig().getHiveStylePartitioningEnable());
+  }
+
+  @Override
+  protected List<String> getExpiredPartitionsForTimeStrategy(List<String> 
partitionPathsForTTL) {
+    long cutoffMillis = resolveCutoffMillis(instantTime, ttlInMilis);
+    DateTimeFormatter formatter = 
DateTimeFormatter.ofPattern(eventTimeFormat).withZone(ZoneOffset.UTC);
+    int segCount = segmentCount(eventTimeFormat);
+    return partitionPathsForTTL.stream().parallel()
+        .filter(path -> isPartitionExpiredByEventTime(
+            path, formatter, startIndex, segCount, cutoffMillis, 
deleteHiveDefaultPartition, hiveStylePartitioning))
+        .collect(Collectors.toList());
+  }
+
+  /**
+   * Number of '/'-separated path segments the configured format occupies.
+   * Example: {@code yyyy-MM-dd/HH} -> 2.
+   */
+  static int segmentCount(String format) {
+    return format.split("/").length;
+  }
+
+  /**
+   * Resolve the "now" reference timestamp from {@code instantTime}, in UTC.
+   * <p>
+   * Anchoring on {@code instantTime} keeps the strategy idempotent across 
retries of the same
+   * replace commit. We parse it in UTC so the cutoff and the partition's 
event time (also parsed
+   * in UTC above) sit on the same axis -- otherwise expiry drifts by the 
JVM's UTC offset, which
+   * is negligible at day granularity but a full-offset shift at hour 
granularity.
+   */
+  static long resolveCutoffMillis(String instantTime, long ttlInMillis) {
+    try {
+      return HoodieInstantTimeGenerator.parseDateFromInstantTime(instantTime, 
ZoneOffset.UTC).getTime() - ttlInMillis;
+    } catch (ParseException e) {
+      throw new IllegalStateException("Failed to parse instant time " + 
instantTime, e);
+    }
+  }
+
+  /**
+   * Decide whether a partition path is expired.
+   * <p>
+   * The strategy treats any partition that cannot be parsed under the 
configured format /
+   * start-index / hive-style as a hard error. Reasoning: this class derives 
lifetime from the
+   * path itself, so a partition we cannot parse has no defined lifetime, and 
silently skipping
+   * it would leave it in the table forever while the rest of TTL appears to 
succeed. Switch to
+   * {@code KEEP_BY_TIME} or {@code KEEP_BY_CREATION_TIME} (which key off 
commit metadata, not
+   * the path) if the table contains partitions that don't conform to a single 
event-time shape.
+   * <p>
+   * Package-private so unit tests can exercise it directly without spinning 
up a HoodieTable.
+   */
+  static boolean isPartitionExpiredByEventTime(String partitionPath,
+                                               DateTimeFormatter formatter,
+                                               int startIndex,
+                                               int segCount,
+                                               long cutoffMillis,
+                                               boolean 
deleteHiveDefaultPartition,
+                                               boolean hiveStylePartitioning) {
+    String[] segments = partitionPath.split("/");
+    if (segments.length < startIndex + segCount) {
+      throw new IllegalArgumentException(String.format(
+          "Partition '%s' has %d segment(s) but the configured event time 
spans %d segment(s) starting at index %d. "
+              + "Check hoodie.partition.ttl.strategy.event.time.format and 
event.time.partition.start.index, "
+              + "or switch to KEEP_BY_TIME / KEEP_BY_CREATION_TIME if not all 
partitions of this table follow an event-time shape.",
+          partitionPath, segments.length, segCount, startIndex));
+    }
+
+    String[] timeSegs = new String[segCount];
+    for (int i = 0; i < segCount; i++) {
+      String seg = segments[startIndex + i];
+      if (hiveStylePartitioning) {
+        int eq = seg.indexOf('=');
+        if (eq < 0) {
+          throw new IllegalArgumentException(String.format(
+              "Partition '%s' segment '%s' has no hive-style 'field=value' 
prefix but "
+                  + "hoodie.datasource.write.hive_style_partitioning=true on 
the table. "
+                  + "Switch to KEEP_BY_TIME / KEEP_BY_CREATION_TIME if such 
legacy partitions must coexist.",
+              partitionPath, seg));
+        }
+        timeSegs[i] = seg.substring(eq + 1);
+      } else {
+        timeSegs[i] = seg;
+      }
+      if (PartitionPathEncodeUtils.DEFAULT_PARTITION_PATH.equals(timeSegs[i])) 
{

Review Comment:
   🤖 In the current revision this is gated rather than unconditional: with 
`deleteHiveDefaultPartition=false` (the default) any time block containing 
`__HIVE_DEFAULT_PARTITION__` in any segment is skipped with a WARN (`return 
false` at line 254), so a recent `dt=2026-06-28/hh=__HIVE_DEFAULT_PARTITION__` 
is retained unless the user explicitly opts in. The rationale — a NULL hour 
column means the event time can't be placed on the axis at all, so the whole 
block is treated as undefined — is now documented at lines 239-244, which 
addresses the "dropping a recent partition" concern.



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