KoP: Broker Index Ordering Issues in Ledger Entries Due to Write Failure

[zhaizhibo]

When performing a write operation to a single ledger in Pulsar, the KoP interceptor calls intercepter.beforeAddEntry() before the write completes, which increments the broker’s index for the corresponding ledger. For example, request A calls this method and gets index1, which is then written into the entry. If request B arrives concurrently, it also calls intercepter.beforeAddEntry() and gets index2, which is written into the entry.

The issue arises when request A fails and its indexGenerator is rolled back, but request B’s write operation succeeds, meaning the entry for request B still contains the incorrect index2. Furthermore, if a subsequent request C is processed and its index index3 turns out to be smaller than index2, the brokerIndex in entries within the same ledger will no longer be strictly increasing. This non-monotonic sequence can lead to unexpected behavior in KoP when performing binary searches for the entry corresponding to a given offset. This issue requires further investigation to ensure that ledger entries maintain a correct monotonically increasing index even in scenarios where write operations fail and rollbacks occur.