BewareMyPower commented on issue #12616:
URL: https://github.com/apache/pulsar/issues/12616#issuecomment-966144710
@Jason918
`internalTrimLedgers` should not update the `lastConfirmedEntry`, which
represents an entry that has been written to BK successfully. After a rollover,
the `lastConfirmedEntry` could be invalid if the ledger was removed. However,
there is no proper new value for it. So we should just keep it unchanged.
See `ManagedLedgerImpl#getFirstPosition`, which handles the corner case.
```java
public PositionImpl getFirstPosition() {
Long ledgerId = ledgers.firstKey();
if (ledgerId == null) {
return null;
}
if (ledgerId > lastConfirmedEntry.getLedgerId()) { // 1. It means
the `lastConfirmedEntry` is invalid
// 2. In this case, the first ledger must be empty because once
a new entry was added, the `lastConfirmedEntry` should be updated.
checkState(ledgers.get(ledgerId).getEntries() == 0);
ledgerId = lastConfirmedEntry.getLedgerId();
}
return new PositionImpl(ledgerId, -1);
}
```
However, the `isValidPosition` check doesn't consider the case when
`lastConfirmedEntry` is invalid.
```java
public boolean isValidPosition(PositionImpl position) {
PositionImpl last = lastConfirmedEntry;
if (position.getEntryId() < 0) {
return false;
} else if (position.getLedgerId() > last.getLedgerId()) {
return false;
} else if (position.getLedgerId() == last.getLedgerId()) {
// `last` could be an invalid position, so even position's
ledger id is the same, it could still be invalid
return position.getEntryId() <= (last.getEntryId() + 1);
} else {
```
Then it affects the `getNextValidPosition` method that is called in KoP to
get the first valid position. You can see
https://github.com/streamnative/kop/pull/894 for more details about how this
corner case is handled in KoP.
But the current `isValidPosition` semantics also affects other methods like
`asyncOffloadPrefix` and `asyncResetCursor`. So we must take it more carefully
to determine whether the semantics should be changed.
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