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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. Maintain only one reader for each namespace.- Loading branch information
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86 changes: 86 additions & 0 deletions
86
...ker/src/main/java/org/apache/pulsar/broker/transaction/buffer/impl/SnapshotTableView.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,86 @@ | ||
| /* | ||
| * 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.systopic.SystemTopicClient.Reader; | ||
| import java.util.Map; | ||
| import java.util.concurrent.CompletableFuture; | ||
| import java.util.concurrent.ConcurrentHashMap; | ||
| import java.util.concurrent.ExecutionException; | ||
| import java.util.concurrent.ScheduledExecutorService; | ||
| import java.util.concurrent.TimeUnit; | ||
| import lombok.extern.slf4j.Slf4j; | ||
| import org.apache.pulsar.broker.service.SystemTopicTxnBufferSnapshotService; | ||
| import org.apache.pulsar.broker.transaction.buffer.metadata.TransactionBufferSnapshot; | ||
| import org.apache.pulsar.common.naming.NamespaceName; | ||
| import org.apache.pulsar.common.naming.TopicName; | ||
| import org.apache.pulsar.utils.SimpleCache; | ||
|
|
||
| /** | ||
| * Compared with the more generic {@link org.apache.pulsar.client.api.TableView}, this table view | ||
| * - Provides just a single public method that reads the latest value synchronously. | ||
| * - Maintains multiple long-lived readers that will be expired after some time (1 minute by default). | ||
| */ | ||
| @Slf4j | ||
| public class SnapshotTableView { | ||
|
|
||
| // Remove the cached reader and snapshots if there is no refresh request in 1 minute | ||
| private static final long CACHE_EXPIRE_TIMEOUT_MS = 60 * 1000L; | ||
| private final Map<String, TransactionBufferSnapshot> snapshots = new ConcurrentHashMap<>(); | ||
| private final SystemTopicTxnBufferSnapshotService<TransactionBufferSnapshot> snapshotService; | ||
| private final long blockTimeoutMs; | ||
| private final SimpleCache<NamespaceName, Reader<TransactionBufferSnapshot>> readers; | ||
|
|
||
| public SnapshotTableView(SystemTopicTxnBufferSnapshotService<TransactionBufferSnapshot> snapshotService, | ||
| ScheduledExecutorService executor, long blockTimeoutMs) { | ||
| this.snapshotService = snapshotService; | ||
| this.blockTimeoutMs = blockTimeoutMs; | ||
| this.readers = new SimpleCache<>(executor, CACHE_EXPIRE_TIMEOUT_MS); | ||
| } | ||
|
|
||
| public TransactionBufferSnapshot readLatest(String topic) throws Exception { | ||
| final var topicName = TopicName.get(topic); | ||
| final var namespace = topicName.getNamespaceObject(); | ||
| final var reader = readers.get(namespace, () -> { | ||
| try { | ||
| return wait(snapshotService.createReader(topicName), "create reader"); | ||
| } catch (Exception e) { | ||
| throw new RuntimeException(e); | ||
| } | ||
| }, __ -> __.closeAsync().exceptionally(e -> { | ||
| log.warn("Failed to close reader {}", e.getMessage()); | ||
| return null; | ||
| })); | ||
| while (wait(reader.hasMoreEventsAsync(), "has more events")) { | ||
| final var msg = wait(reader.readNextAsync(), "read message"); | ||
| if (msg.getKey() != null) { | ||
| snapshots.put(msg.getKey(), msg.getValue()); | ||
| } | ||
| } | ||
| return snapshots.get(topic); | ||
| } | ||
|
|
||
| private <T> T wait(CompletableFuture<T> future, String msg) throws Exception { | ||
| try { | ||
| return future.get(blockTimeoutMs, TimeUnit.MILLISECONDS); | ||
| } catch (ExecutionException e) { | ||
| throw new ExecutionException("Failed to " + msg, e.getCause()); | ||
| } | ||
| } | ||
| } |
62 changes: 62 additions & 0 deletions
62
pulsar-broker/src/main/java/org/apache/pulsar/utils/SimpleCache.java
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|---|---|---|
| @@ -0,0 +1,62 @@ | ||
| /* | ||
| * 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.utils; | ||
|
|
||
| import java.util.HashMap; | ||
| import java.util.Map; | ||
| import java.util.concurrent.ScheduledExecutorService; | ||
| import java.util.concurrent.ScheduledFuture; | ||
| import java.util.concurrent.TimeUnit; | ||
| import java.util.function.Consumer; | ||
| import java.util.function.Supplier; | ||
| import lombok.RequiredArgsConstructor; | ||
|
|
||
| @RequiredArgsConstructor | ||
| public class SimpleCache<K, V> { | ||
|
|
||
| private final Map<K, V> cache = new HashMap<>(); | ||
| private final Map<K, ScheduledFuture<?>> futures = new HashMap<>(); | ||
| private final ScheduledExecutorService executor; | ||
| private final long timeoutMs; | ||
|
|
||
| public synchronized V get(final K key, final Supplier<V> valueSupplier, final Consumer<V> expireCallback) { | ||
| final V value; | ||
| V existingValue = cache.get(key); | ||
| if (existingValue != null) { | ||
| value = existingValue; | ||
| } else { | ||
| value = valueSupplier.get(); | ||
| cache.put(key, value); | ||
| } | ||
| final var future = futures.remove(key); | ||
| if (future != null) { | ||
| future.cancel(true); | ||
| } | ||
| futures.put(key, executor.schedule(() -> { | ||
| synchronized (SimpleCache.this) { | ||
| futures.remove(key); | ||
| final var removedValue = cache.remove(key); | ||
| if (removedValue != null) { | ||
| expireCallback.accept(removedValue); | ||
| } | ||
| } | ||
| }, timeoutMs, TimeUnit.MILLISECONDS)); | ||
| return value; | ||
| } | ||
| } |
74 changes: 74 additions & 0 deletions
74
pulsar-broker/src/test/java/org/apache/pulsar/utils/SimpleCacheTest.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,74 @@ | ||
| /* | ||
| * 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.utils; | ||
|
|
||
| import java.util.Collections; | ||
| import java.util.concurrent.CopyOnWriteArrayList; | ||
| import java.util.concurrent.CountDownLatch; | ||
| import java.util.concurrent.Executors; | ||
| import java.util.concurrent.ScheduledExecutorService; | ||
| import org.testng.Assert; | ||
| import org.testng.annotations.AfterClass; | ||
| import org.testng.annotations.Test; | ||
|
|
||
| public class SimpleCacheTest { | ||
|
|
||
| private final ScheduledExecutorService executor = Executors.newScheduledThreadPool(1); | ||
|
|
||
| @AfterClass | ||
| public void shutdown() { | ||
| executor.shutdown(); | ||
| } | ||
|
|
||
| @Test | ||
| public void testConcurrentUpdate() throws Exception { | ||
| final var cache = new SimpleCache<Integer, Integer>(executor, 10000L); | ||
| final var pool = Executors.newFixedThreadPool(2); | ||
| final var latch = new CountDownLatch(2); | ||
| for (int i = 0; i < 2; i++) { | ||
| final var value = i + 100; | ||
| pool.execute(() -> { | ||
| try { | ||
| Thread.sleep(100); | ||
| } catch (InterruptedException ignored) { | ||
| } | ||
| cache.get(0, () -> value, __ -> {}); | ||
| latch.countDown(); | ||
| }); | ||
| } | ||
| latch.await(); | ||
| final var value = cache.get(0, () -> -1, __ -> {}); | ||
| Assert.assertTrue(value == 100 || value == 101); | ||
| pool.shutdown(); | ||
| } | ||
|
|
||
| @Test | ||
| public void testExpire() throws InterruptedException { | ||
| final var cache = new SimpleCache<Integer, Integer>(executor, 500L); | ||
| final var expiredValues = new CopyOnWriteArrayList<Integer>(); | ||
| cache.get(0, () -> 100, expiredValues::add); | ||
| for (int i = 0; i < 100; i++) { | ||
| cache.get(1, () -> 101, expiredValues::add); | ||
| Thread.sleep(10); | ||
| } | ||
| Assert.assertEquals(cache.get(0, () -> -1, __ -> {}), -1); // the value is expired | ||
| Assert.assertEquals(cache.get(1, () -> -1, __ -> {}), 101); | ||
| Assert.assertEquals(expiredValues, Collections.singletonList(100)); | ||
| } | ||
| } |