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[improve][broker] Reduce the pressure from the transaction buffer rea…
…ders and writers in rolling restarts
### Motivation
During the rolling restarts, the namespace bundle ownerships will
change. Assuming there is a producer created on a single topic, and the
ownership was transferred to the new broker. Assuming the namespace
bundle has N topics and the namespace is `tenant/ns`,
1. All N topics in the same bundle of that topic will be loaded.
2. For each topic, the managed ledger will be initialized, when the
transaction coordinator is enabled, a `TopicTransactionBuffer` will
be created.
2.1 A Pulsar producer will be created on
`tenant/ns/__transaction_buffer_snapshot` concurrently.
2.2 A Pulsar reader will be created on
`tenant/ns/__transaction_buffer_snapshot` concurrently.
3. Once all N readers are created, the owner of the snapshot topic will
start dispatching messages to N readers. Each dispatcher will read
messages from BookKeeper concurrently and might fail with too many
requests error because BK can only have
`maxPendingReadRequestsPerThread` pending read requests (default: 10000).
We have a `numTransactionReplayThreadPoolSize` config to limit the
concurrency of transaction snapshot readers. However, it only limits the
read loop. For example, if it's configured with 1, only 1 reader could
read messages at the same time. However, N readers will be created
concurrently. Each when one of these reader explicitly calls `readNext`,
all N dispatchers at brokers side will dispatch messages to N readers.
The behaviors above brings much CPU pressure on the owner broker,
especially for a small cluster with only two brokers.
### Modifications
- Synchronize the reader creation, read loop and the following process
on its result.
- Delay the snapshot producer creaton to when a message is written via
`LazySnapshotWriter`.- Loading branch information
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...er/src/main/java/org/apache/pulsar/broker/transaction/buffer/impl/LazySnapshotWriter.java
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| /* | ||
| * Licensed to the Apache Software Foundation (ASF) under one | ||
| * or more contributor license agreements. See the NOTICE file | ||
| * distributed with this work for additional information | ||
| * regarding copyright ownership. The ASF licenses this file | ||
| * to you under the Apache License, Version 2.0 (the | ||
| * "License"); you may not use this file except in compliance | ||
| * with the License. You may obtain a copy of the License at | ||
| * | ||
| * http://www.apache.org/licenses/LICENSE-2.0 | ||
| * | ||
| * Unless required by applicable law or agreed to in writing, | ||
| * software distributed under the License is distributed on an | ||
| * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY | ||
| * KIND, either express or implied. See the License for the | ||
| * specific language governing permissions and limitations | ||
| * under the License. | ||
| */ | ||
| package org.apache.pulsar.broker.transaction.buffer.impl; | ||
|
|
||
| import static org.apache.pulsar.broker.service.SystemTopicTxnBufferSnapshotService.ReferenceCountedWriter; | ||
| import static org.apache.pulsar.broker.systopic.SystemTopicClient.Writer; | ||
| import java.util.concurrent.CompletableFuture; | ||
| import lombok.extern.slf4j.Slf4j; | ||
| import org.apache.pulsar.broker.service.SystemTopicTxnBufferSnapshotService; | ||
| import org.apache.pulsar.broker.service.persistent.PersistentTopic; | ||
| import org.apache.pulsar.common.naming.TopicName; | ||
|
|
||
| @Slf4j | ||
| public class LazySnapshotWriter<T> { | ||
|
|
||
| private final PersistentTopic topic; | ||
| private final SystemTopicTxnBufferSnapshotService<T> snapshotService; | ||
| private ReferenceCountedWriter<T> writer; | ||
|
|
||
| public LazySnapshotWriter(PersistentTopic topic, SystemTopicTxnBufferSnapshotService<T> snapshotService) { | ||
| this.topic = topic; | ||
| this.snapshotService = snapshotService; | ||
| } | ||
|
|
||
| public synchronized CompletableFuture<Writer<T>> getFuture() { | ||
| if (writer != null) { | ||
| return writer.getFuture(); | ||
| } | ||
| writer = snapshotService.getReferenceWriter(TopicName.get(topic.getName()).getNamespaceObject()); | ||
| final var future = writer.getFuture(); | ||
| future.exceptionally(e -> { | ||
| synchronized (LazySnapshotWriter.this) { | ||
| // Next time `getWriter()` is called, the writer will be recreated | ||
| writer = null; | ||
| } | ||
| log.error("{} Failed to create snapshot writer", topic.getName(), e); | ||
| return null; | ||
| }); | ||
| return future; | ||
| } | ||
|
|
||
| public synchronized void release() { | ||
| if (writer != null) { | ||
| writer.release(); | ||
| } | ||
| } | ||
| } |
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