Fix producer stuck issue due to NPE thrown when creating a new ledger

[sijie]

Motivation

NPE can be thrown when creating a ledger because the network address is unresolvable. If NPE is thrown before adding the timeout task, the timeout mechanism doesn't work.

Network address unresolvable is commonly seen in the Kubernetes environment. It can happen when a bookie pod or a worker node restarts.

Changes

This pull request does the followings:

1. Catch the NPE when creating a new ledger.
2. When the timeout task is triggered, always execute the callback. It is totally fine because we already have the logic to ensure the callback is triggered only once.
3. Add a mechanism to detect the CreatingLedger state is not moving.

[merlimat]

Try-catch here is good in any case, though we should also ensure that BK client is handling DNS errors by triggering the callback instead of exception.

[sijie]

The fix was already made in the bookkeeper client. We don't release the bookkeeper client yet.

[merlimat]

Is this change intentional?

Shouldn't the callback only be triggered if (!ledgerCreated.get()) ?

[sijie]

It is intentional - when the timeout task is triggered, always execute the callback. It is totally fine because we already have the logic to ensure the callback is triggered only once.

This change ensures all the logic is executed in a central place instead of spreading across multiple places and can potentially make code maintenance much harder.

[merlimat]

@sijie One more thing. There are a couple more calls to create ledgers, we should then do try/catch on all of them:

$ git grep '\.asyncCreateLedger' | grep -v test
managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/ManagedCursorImpl.java:        ledger.asyncCreateLedger(bookkeeper, config, digestType, (rc, lh, ctx) -> {
managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/ManagedLedgerImpl.java:            bookKeeper.asyncCreateLedger(config.getEnsembleSize(), config.getWriteQuorumSize(), config.getAckQuorumSize(),
pulsar-broker/src/main/java/org/apache/pulsar/broker/service/schema/BookkeeperSchemaStorage.java:        bookKeeper.asyncCreateLedger(
pulsar-broker/src/main/java/org/apache/pulsar/compaction/TwoPhaseCompactor.java:        bk.asyncCreateLedger(conf.getManagedLedgerDefaultEnsembleSize(),

[merlimat]

Anyway, we can do in separate PR. But my next question is: can the NPE also happen on asyncAddEntry() calls?

[sijie]

@merlimat the DNS resolution problem only happens when creating a ledger. So it doesn't happen on adding entries.

I think we should release a bug fix release on bookkeeper soon.