ableegoldman commented on a change in pull request #9157:
URL: https://github.com/apache/kafka/pull/9157#discussion_r485221931



##########
File path: 
streams/src/main/java/org/apache/kafka/streams/kstream/internals/KStreamSlidingWindowAggregate.java
##########
@@ -146,96 +165,203 @@ public void processInOrder(final K key, final V value, 
final long timestamp) {
             boolean leftWinAlreadyCreated = false;
             boolean rightWinAlreadyCreated = false;
 
-            // keep the left type window closest to the record
-            Window latestLeftTypeWindow = null;
+            Long previousRecordTimestamp = null;
+
             try (
                 final KeyValueIterator<Windowed<K>, ValueAndTimestamp<Agg>> 
iterator = windowStore.fetch(
                     key,
                     key,
-                    timestamp - 2 * windows.timeDifferenceMs(),
+                    Math.max(0, inputRecordTimestamp - 2 * 
windows.timeDifferenceMs()),
                     // to catch the current record's right window, if it 
exists, without more calls to the store
-                    timestamp + 1)
+                    inputRecordTimestamp + 1)
             ) {
                 while (iterator.hasNext()) {
-                    final KeyValue<Windowed<K>, ValueAndTimestamp<Agg>> next = 
iterator.next();
-                    windowStartTimes.add(next.key.window().start());
-                    final long startTime = next.key.window().start();
+                    final KeyValue<Windowed<K>, ValueAndTimestamp<Agg>> 
windowBeingProcessed = iterator.next();
+                    final long startTime = 
windowBeingProcessed.key.window().start();
+                    windowStartTimes.add(startTime);
                     final long endTime = startTime + 
windows.timeDifferenceMs();
+                    final long windowMaxRecordTimestamp = 
windowBeingProcessed.value.timestamp();
 
-                    if (endTime < timestamp) {
-                        leftWinAgg = next.value;
-                        if (isLeftWindow(next)) {
-                            latestLeftTypeWindow = next.key.window();
-                        }
-                    } else if (endTime == timestamp) {
+                    if (endTime < inputRecordTimestamp) {
+                        leftWinAgg = windowBeingProcessed.value;
+                        previousRecordTimestamp = windowMaxRecordTimestamp;
+                    } else if (endTime == inputRecordTimestamp) {
                         leftWinAlreadyCreated = true;
-                        putAndForward(next.key.window(), next.value, key, 
value, closeTime, timestamp);
-                    } else if (endTime > timestamp && startTime <= timestamp) {
-                        rightWinAgg = next.value;
-                        putAndForward(next.key.window(), next.value, key, 
value, closeTime, timestamp);
-                    } else {
+                        if (windowMaxRecordTimestamp < inputRecordTimestamp) {
+                            previousRecordTimestamp = windowMaxRecordTimestamp;
+                        }
+                        
updateWindowAndForward(windowBeingProcessed.key.window(), 
windowBeingProcessed.value, key, value, closeTime, inputRecordTimestamp);
+                    } else if (endTime > inputRecordTimestamp && startTime <= 
inputRecordTimestamp) {
+                        rightWinAgg = windowBeingProcessed.value;
+                        
updateWindowAndForward(windowBeingProcessed.key.window(), 
windowBeingProcessed.value, key, value, closeTime, inputRecordTimestamp);
+                    } else if (startTime == inputRecordTimestamp + 1) {
                         rightWinAlreadyCreated = true;
+                    } else {
+                        throw new IllegalStateException("Unexpected window 
found when processing sliding windows");
                     }
                 }
             }
 
             //create right window for previous record
-            if (latestLeftTypeWindow != null) {
-                final long rightWinStart = latestLeftTypeWindow.end() + 1;
-                if (!windowStartTimes.contains(rightWinStart)) {
-                    final TimeWindow window = new TimeWindow(rightWinStart, 
rightWinStart + windows.timeDifferenceMs());
-                    final ValueAndTimestamp<Agg> valueAndTime = 
ValueAndTimestamp.make(initializer.apply(), timestamp);
-                    putAndForward(window, valueAndTime, key, value, closeTime, 
timestamp);
+            if (previousRecordTimestamp != null) {
+                final long previousRightWinStart = previousRecordTimestamp + 1;
+                if (rightWindowNecessaryAndPossible(windowStartTimes, 
previousRightWinStart, inputRecordTimestamp)) {
+                    final TimeWindow window = new 
TimeWindow(previousRightWinStart, previousRightWinStart + 
windows.timeDifferenceMs());
+                    final ValueAndTimestamp<Agg> valueAndTime = 
ValueAndTimestamp.make(initializer.apply(), inputRecordTimestamp);
+                    updateWindowAndForward(window, valueAndTime, key, value, 
closeTime, inputRecordTimestamp);
                 }
             }
 
             //create left window for new record
             if (!leftWinAlreadyCreated) {
                 final ValueAndTimestamp<Agg> valueAndTime;
-                //there's a right window that the new record could create --> 
new record's left window is not empty
-                if (latestLeftTypeWindow != null) {
-                    valueAndTime = ValueAndTimestamp.make(leftWinAgg.value(), 
timestamp);
+                // if there's a right window that the new record could create 
&& previous record falls within left window -> new record's left window is not 
empty
+                if (leftWindowNotEmpty(previousRecordTimestamp, 
inputRecordTimestamp)) {
+                    valueAndTime = ValueAndTimestamp.make(leftWinAgg.value(), 
inputRecordTimestamp);
                 } else {
-                    valueAndTime = ValueAndTimestamp.make(initializer.apply(), 
timestamp);
+                    valueAndTime = ValueAndTimestamp.make(initializer.apply(), 
inputRecordTimestamp);
                 }
-                final TimeWindow window = new TimeWindow(timestamp - 
windows.timeDifferenceMs(), timestamp);
-                putAndForward(window, valueAndTime, key, value, closeTime, 
timestamp);
+                final TimeWindow window = new TimeWindow(inputRecordTimestamp 
- windows.timeDifferenceMs(), inputRecordTimestamp);
+                updateWindowAndForward(window, valueAndTime, key, value, 
closeTime, inputRecordTimestamp);
             }
-            //create right window for new record
-            if (!rightWinAlreadyCreated && rightWindowIsNotEmpty(rightWinAgg, 
timestamp)) {
-                final TimeWindow window = new TimeWindow(timestamp + 1, 
timestamp + 1 + windows.timeDifferenceMs());
-                final ValueAndTimestamp<Agg> valueAndTime = 
ValueAndTimestamp.make(getValueOrNull(rightWinAgg), 
Math.max(rightWinAgg.timestamp(), timestamp));
-                putAndForward(window, valueAndTime, key, value, closeTime, 
timestamp);
+            if (!rightWinAlreadyCreated && rightWindowIsNotEmpty(rightWinAgg, 
inputRecordTimestamp)) {
+                createCurrentRecordRightWindow(inputRecordTimestamp, 
rightWinAgg, key);
             }
         }
 
-        private boolean rightWindowIsNotEmpty(final ValueAndTimestamp<Agg> 
rightWinAgg, final long timestamp) {
-            return rightWinAgg != null && rightWinAgg.timestamp() > timestamp;
+        /**
+         * Created to handle records where 0 < inputRecordTimestamp < 
timeDifferenceMs. These records would create
+         * windows with negative start times, which is not supported. Instead, 
we will put them into the [0, timeDifferenceMs]
+         * window as a "workaround", and we will update or create their right 
windows as new records come in later
+         */
+        private void processEarly(final K key, final V value, final long 
inputRecordTimestamp, final long closeTime) {
+            if (inputRecordTimestamp < 0 || inputRecordTimestamp >= 
windows.timeDifferenceMs()) {
+                throw new IllegalArgumentException("Early record for sliding 
windows must fall between 0 < inputRecordTimestamp < timeDifferenceMs");

Review comment:
       nit: log an error and include the `inputRecordTimestamp` 




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