[GitHub] [kafka] vvcephei commented on a change in pull request #9137: KAFKA-9929: Support reverse iterator on KeyValueStore

[GitBox <gi...@apache.org>]

vvcephei commented on a change in pull request #9137:
URL: https://github.com/apache/kafka/pull/9137#discussion_r472531237



##########
File path: streams/src/main/java/org/apache/kafka/streams/state/internals/RocksDBPrefixIterator.java
##########
@@ -1,54 +0,0 @@
-/*
- * 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.kafka.streams.state.internals;
-
-import org.apache.kafka.common.utils.Bytes;
-import org.apache.kafka.streams.state.KeyValueIterator;
-import org.rocksdb.RocksIterator;
-
-import java.util.Set;
-
-class RocksDBPrefixIterator extends RocksDbIterator {

Review comment:
       Was this class unused or something?

##########
File path: streams/src/main/java/org/apache/kafka/streams/state/internals/CachingKeyValueStore.java
##########
@@ -249,7 +248,23 @@ public void putAll(final List<KeyValue<Bytes, byte[]>> entries) {
         validateStoreOpen();
         final KeyValueIterator<Bytes, byte[]> storeIterator = wrapped().range(from, to);
         final ThreadCache.MemoryLRUCacheBytesIterator cacheIterator = context.cache().range(cacheName, from, to);
-        return new MergedSortedCacheKeyValueBytesStoreIterator(cacheIterator, storeIterator);
+        return new MergedSortedCacheKeyValueBytesStoreIterator(cacheIterator, storeIterator, false);
+    }
+
+    @Override
+    public KeyValueIterator<Bytes, byte[]> reverseRange(final Bytes from,
+                                                        final Bytes to) {
+        if (from.compareTo(to) > 0) {
+            LOG.warn("Returning empty iterator for fetch with invalid key range: from > to. "
+                + "This may be due to serdes that don't preserve ordering when lexicographically comparing the serialized bytes. " +
+                "Note that the built-in numerical serdes do not follow this for negative numbers");

Review comment:
       This warning seems to miss the most likely scenario, that the user just passed the arguments in the wrong order.




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