[KAFKA-13309] InMemorySessionStore#fetch/backwardFetch doesn't return in correct order

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.0.0
• Fix Version/s: 3.1.0, 3.0.1
• Component/s: streams
• Assignee: Luke Chen
• Reporter: Luke Chen
• Created: 17/Sep/21 12:33
• Updated: 30/Sep/21 00:44
• Resolved: 29/Sep/21 00:35

Description

We supported backward iterator for SessionStore in KAFKA-9929. But we cannot return the correct order when fetch/backwardFetch the key range when there are multiple records in the same session window.

For example:

We have a session window inactivity gap with 10 ms, and the records:

key: "A", value: "AA", timestamp: 0 --> with SessionWindow(0, 0)

key: "B", value: "BB", timestamp: 0 --> with SessionWindow(0, 0)

key: "C", value: "CC", timestamp: 0 --> with SessionWindow(0, 0)

key: "D" value: "DD", timestamp: 100 --> with SessionWindow(100, 100)

 

So, when fetch("A" /*key from*/, "D" /*key to*/), we expected to have [A, B, C, D], but we'll have [C, B A, D ]

 

And the reason is here:

https://github.com/apache/kafka/blob/trunk/streams/src/main/java/org/apache/kafka/streams/state/internals/InMemorySessionStore.java#L276-L295

 

public KeyValueIterator<Windowed<Bytes>, byte[]> fetch(final Bytes keyFrom, final Bytes keyTo) {
                return registerNewIterator(keyFrom, keyTo, Long.MAX_VALUE, endTimeMap.entrySet().iterator(), false); // <-- the final param is "isFarwarded", which should be true for "fetch" case, and false for "backwardFetch" case
            }

We pass "false" in the "is forward" parameter for `fetch` method, and "true" for "backwardFetch" method, which obviously is wrong.

 

Issue Links

• links to: GitHub Pull Request #11337