horizonzy commented on PR #3917:
URL: https://github.com/apache/bookkeeper/pull/3917#issuecomment-1507285235
> How the lastAddConfirm was generated
> Due to the ledger being in the OPEN state, the ledger handle will send a
readLAC request to get the ledger's lastAddConfirm.
> For the above case, if bk1 holds the max entry 14, bk2 holds the max entry
13 and bk3 holds the max entry 14 but it is lost, the LedgerHandle get
lastAddConfirm will be 13, not 14.
I have a question about this.
```
public void checkLedger(final LedgerHandle lh,
final GenericCallback<Set<LedgerFragment>> cb,
long percentageOfLedgerFragmentToBeVerified)
```
There are two places to invoke LedgerChecker#checkLedger.
1.
https://github.com/apache/bookkeeper/blob/35e9da9b55b5d44459d3421e8704be47afc6f914/bookkeeper-server/src/main/java/org/apache/bookkeeper/replication/AuditorCheckAllLedgersTask.java#L196-L212
2.https://github.com/apache/bookkeeper/blob/35e9da9b55b5d44459d3421e8704be47afc6f914/bookkeeper-server/src/main/java/org/apache/bookkeeper/replication/ReplicationWorker.java#L449-L451
Both places use the openLedgerNoRecovery to open the LedgerHandle.
It will use lh.asyncReadLastConfirmed() to get the LAC.
https://github.com/apache/bookkeeper/blob/35e9da9b55b5d44459d3421e8704be47afc6f914/bookkeeper-server/src/main/java/org/apache/bookkeeper/client/LedgerOpenOp.java#L222-L245
And we use the V2 protocol, it invokes `asyncReadPiggybackLastConfirmed`.
https://github.com/apache/bookkeeper/blob/35e9da9b55b5d44459d3421e8704be47afc6f914/bookkeeper-server/src/main/java/org/apache/bookkeeper/client/LedgerHandle.java#L1388-L1395
In asyncReadPiggybackLastConfirmed, it invokes
ReadLastConfirmedOp#initiate() to get the LAC.
https://github.com/apache/bookkeeper/blob/35e9da9b55b5d44459d3421e8704be47afc6f914/bookkeeper-server/src/main/java/org/apache/bookkeeper/client/LedgerHandle.java#L1422-L1428
In the ReadLastConfirmedOp, it will read all bookies in the currentEnsemble.
The currentEnsemble is `15=[bk1:3181, bk2:3181, bk4:3181]`. Not the
{0=[bk1:3181, bk2:3181, bk3:3181].
So it will send readLac RPC to bk1, bk2, and bk4. Then get response from
bk1, bk2, and bk4.
When ReadLastConfirmedOp#readEntryComplete, it will compare the response
from different bookies, then pick the max lac response to override
maxRecoveredData. Then invoke the callback using the maxRecoveredData.
So if the bk1 lac is 14, the ledgerHandle lac should be 14, not 13.
https://github.com/apache/bookkeeper/blob/35e9da9b55b5d44459d3421e8704be47afc6f914/bookkeeper-server/src/main/java/org/apache/bookkeeper/client/ReadLastConfirmedOp.java#L197-L154
line_l08-line_112, it will pick the max lac to override maxRecoveredData.
line_137-line_148, use the maxRecoveredData to invoke callback.
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