Fix CPU 100% when deleting namespace

[315157973]

Motivation

When deleting the namespace, the namespace Policies will be marked as deleted.
This will trigger topic's onPoliciesUpdate
However, in onPoliciesUpdate, the data of the Policies node on zk will be read, such as: checkReplicationAndRetryOnFailure
Due to the deletion of the namespace, the zk node may no longer exist at this time.
Failure to read data will trigger infinite retries.

pulsar/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/persistent/PersistentTopic.java

Lines 1175 to 1193 in e970c29

	private CompletableFuture<Void> checkReplicationAndRetryOnFailure() {
	CompletableFuture<Void> result = new CompletableFuture<Void>();
	checkReplication().thenAccept(res -> {
	log.info("[{}] Policies updated successfully", topic);
	result.complete(null);
	}).exceptionally(th -> {
	log.error("[{}] Policies update failed {}, scheduled retry in {} seconds", topic, th.getMessage(),
	POLICY_UPDATE_FAILURE_RETRY_TIME_SECONDS, th);
	if (!(th.getCause() instanceof TopicFencedException)) {
	// retriable exception
	brokerService.executor().schedule(this::checkReplicationAndRetryOnFailure,
	POLICY_UPDATE_FAILURE_RETRY_TIME_SECONDS, TimeUnit.SECONDS);
	}
	result.completeExceptionally(th);
	return null;
	});
	return result;
	}

If there are many topics, there will be a short-term CPU spike

Modifications

Verifying this change

[eolivelli]

CN we add a positive test, that verifies that this method is called in case of non deleted Policies?

[eolivelli]

Perfect
Thanks

[eolivelli]

@315157973
this patch does not apply to branch-2.7
can you please create a new PR for branch-2.7 ?

[eolivelli]

@315157973 thank you for porting this patch to branch-2.7.
I have included it in 2.7.2rc1