vamossagar12 commented on a change in pull request #10052:
URL: https://github.com/apache/kafka/pull/10052#discussion_r575662025
##########
File path:
streams/src/test/java/org/apache/kafka/streams/state/internals/InMemoryKeyValueStoreTest.java
##########
@@ -60,4 +67,22 @@ public void shouldRemoveKeysWithNullValues() {
assertThat(store.get(0), nullValue());
}
+
+
+ @Test
+ public void shouldReturnKeysWithGivenPrefix(){
+ store = createKeyValueStore(driver.context());
+ final String value = "value";
+ final List<KeyValue<Integer, String>> entries = new ArrayList<>();
+ entries.add(new KeyValue<>(1, value));
+ entries.add(new KeyValue<>(2, value));
+ entries.add(new KeyValue<>(11, value));
+ entries.add(new KeyValue<>(13, value));
+
+ store.putAll(entries);
+ final KeyValueIterator<Integer, String> keysWithPrefix =
store.prefixScan(1, new IntegerSerializer());
Review comment:
I spent some more time on this today. What seems to be happening here is
that in InMemoryKVStore, even though we are creating a NavigableMap as the
inner map and even though Bytes(Key type for the inner map) does implement
Comparable, when I insert the following keys:
```final List<KeyValue<Integer, String>> entries = new ArrayList<>();
entries.add(new KeyValue<>(1, value));
entries.add(new KeyValue<>(2, value));
entries.add(new KeyValue<>(11, value));
entries.add(new KeyValue<>(13, value));
store.putAll(entries);
```
so the expectation(atleast for me) was that i should get the keys stored
lexicographically ie the output of
```
final KeyValueIterator<Integer, String> allKeys = store.all();
while (allKeys.hasNext()){
System.out.println(allKeys.next().key);
}
```
should be `1 11 13 2` but what gets returned is `1 2 11 13` i.e the order in
which we inserted.
Just to strengthen the point, when I insert keys in the order:
```final List<KeyValue<Integer, String>> entries = new ArrayList<>();
entries.add(new KeyValue<>(1, value));
entries.add(new KeyValue<>(11, value));
entries.add(new KeyValue<>(13, value));
entries.add(new KeyValue<>(2, value));
store.putAll(entries);
```
and when I fetch all keys, what I get back is still `1 2 11 13` i.e the
natural ordering of the integer keys. And this is precisely the reason why
prefix scan is returning only 1 key in the test case that I had pointed out. I
did try to pass in an explicit comparator to the TreeMap but that didn't help
as well. What are your thoughts on this?
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