dao-jun commented on code in PR #22707:
URL: https://github.com/apache/pulsar/pull/22707#discussion_r1624839739
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pulsar-broker/src/main/java/org/apache/pulsar/broker/transaction/buffer/impl/InMemTransactionBuffer.java:
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@@ -307,6 +307,7 @@ public CompletableFuture<Void> commitTxn(TxnID txnID, long
lowWaterMark) {
txnBuffer.commitAt(committedAtLedgerId, committedAtEntryId);
addTxnToTxnIdex(txnID, committedAtLedgerId);
}
+ updateLastDispatchablePosition(null);
Review Comment:
I introduced a filed `lastDispatchablePosition` to store the last position
which is valid to dispatch, in `PersistentTopic`. And before return
`lastDispatchablePosition`, check if `lastDispatchablePosition` is null,
otherwise, search the position in BK.
About why set `lastDispatchablePosition` to null when commit txn, it is
because of it's hard to determine which position to set, so, set to null to
make it fallback to search the position from BK.
> Because transaction committed will not change the previously recorded
stable consumable position into a
> non-consumable position.
I don't agree with this point, after commit a txn, the
`lastDispatchablePosition` may have a chance to move forward, right? But, we
don't know which position to set, and, even though we record the last entry
position of the txn, what if non-txn messages published?
Say, `txn1` contains `1, 2, 3` messages, and we record all the positions.
Before commit `txn1`, there is a new non-txn message `4` published, when commit
`txn1`, what value can we set to `lastDispatchablePosition`? So I set
`lastDispatchablePosition` to null, we can get the `lastDispatchablePosition`
by searching BK.
My point is, the situations here is very complex, right? After commit a
txn, the `lastDispatchablePosition` can be moved forward, or not. A topic
contains `txn messages`, `non-txn messages`, `Marker`; `txn messages` contains
`abort txn`, `ongoing txn`, `commit txn`.
Set `lastDispatchablePosition` to null after commit/abort txn is the easiest
way to make it consistent,
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