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CNDB-12553: ensure that memtable is reclaimed even when notification subscribers throw #1545
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jakubzytka
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cndb-12553-ensure-memtable-reclaimed-when-notification-subscriber-throws
Feb 25, 2025
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223 changes: 223 additions & 0 deletions
223
test/long/org/apache/cassandra/io/memtable/FlushFailingOnNotificationSubscriberTest.java
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| @@ -0,0 +1,223 @@ | ||
| /* | ||
| * 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. | ||
| */ | ||
|
|
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| package org.apache.cassandra.io.memtable; | ||
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| import com.google.common.util.concurrent.AtomicDouble; | ||
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| import org.apache.cassandra.concurrent.DebuggableScheduledThreadPoolExecutor; | ||
| import org.apache.cassandra.config.Config; | ||
| import org.apache.cassandra.config.DatabaseDescriptor; | ||
| import org.apache.cassandra.cql3.CQLTester; | ||
| import org.apache.cassandra.cql3.UntypedResultSet; | ||
| import org.apache.cassandra.db.ColumnFamilyStore; | ||
| import org.apache.cassandra.db.compaction.OperationType; | ||
| import org.apache.cassandra.io.sstable.format.SSTableReader; | ||
| import org.apache.cassandra.notifications.INotification; | ||
| import org.apache.cassandra.notifications.SSTableAddingNotification; | ||
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| import org.junit.BeforeClass; | ||
| import org.junit.Test; | ||
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| import java.util.concurrent.ExecutionException; | ||
| import java.util.concurrent.Future; | ||
| import java.util.concurrent.TimeUnit; | ||
| import java.util.concurrent.TimeoutException; | ||
| import java.util.concurrent.atomic.AtomicInteger; | ||
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|
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| import static java.util.concurrent.TimeUnit.SECONDS; | ||
| import static org.apache.cassandra.db.memtable.AbstractAllocatorMemtable.MEMORY_POOL; | ||
| import static org.junit.Assert.assertEquals; | ||
| import static org.junit.Assert.assertTrue; | ||
|
|
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| /** | ||
| * this is a long-ish test that shows that writes do not block anymore | ||
| * after flush is failing in the notification subscriber | ||
| * <p> | ||
| * without the fix the test fails typically within a couple of seconds | ||
| * by default the test duration is set to 120s | ||
| */ | ||
| public class FlushFailingOnNotificationSubscriberTest extends CQLTester | ||
| { | ||
| private static final int APPROXIMATE_TEST_DURATION_SECONDS = 120; | ||
| private static final double FLUSH_FAILURE_PROBABILITY = 0.25; | ||
| private final AtomicInteger numUserFlushes = new AtomicInteger(); | ||
| private final AtomicInteger numFailedFlushes = new AtomicInteger(); | ||
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| volatile long maxTimeSinceCleanup = 0; | ||
| volatile long lastTimePoolNeededCleaning = System.nanoTime(); | ||
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| static AtomicDouble failFlushProbability = new AtomicDouble(FLUSH_FAILURE_PROBABILITY); | ||
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| @BeforeClass | ||
| public static void setup() | ||
| { | ||
| Config conf = DatabaseDescriptor.getRawConfig(); | ||
| // frequent flushes | ||
| conf.memtable_allocation_type = Config.MemtableAllocationType.offheap_objects; | ||
| conf.memtable_cleanup_threshold = 0.15f; | ||
| conf.memtable_heap_space_in_mb = 2; | ||
| conf.memtable_offheap_space_in_mb = 2; | ||
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| CQLTester.setUpClass(); | ||
| } | ||
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| @Test | ||
| public void flushFailingOnSSTableAddingNotificationVSWritesTest() throws InterruptedException, ExecutionException, TimeoutException | ||
| { | ||
| try | ||
| { | ||
| DebuggableScheduledThreadPoolExecutor scheduledExecutor = new DebuggableScheduledThreadPoolExecutor("forced flush"); | ||
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| createTable(KEYSPACE, "CREATE TABLE %s (pk int PRIMARY KEY, value int)", "failedflushtest"); | ||
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| ColumnFamilyStore cfs = getCurrentColumnFamilyStore(); | ||
| cfs.getTracker().subscribeLateConsumer(this::maybeThrowWhenFlushAddsSSTables); | ||
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| int flushPeriodSec = 15; | ||
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| scheduledExecutor.scheduleAtFixedRate(this::successfulUserFlush, flushPeriodSec, flushPeriodSec, SECONDS); | ||
| scheduledExecutor.scheduleAtFixedRate(() -> { | ||
| updateMaxTimeSinceCleanup(); | ||
| logState(); | ||
| }, 1, 1, SECONDS); | ||
|
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| int idx = 1; | ||
| while (numUserFlushes.get() < APPROXIMATE_TEST_DURATION_SECONDS / flushPeriodSec) | ||
| { | ||
| final int fidx = idx; | ||
| Future<UntypedResultSet> query = scheduledExecutor.submit(() -> execute("INSERT INTO %s (pk, value) VALUES (?, ?)", fidx, fidx)); | ||
| try | ||
| { | ||
| query.get(1, TimeUnit.SECONDS); | ||
| } | ||
| catch (TimeoutException e) | ||
| { | ||
| logger.info("write timed out at iteration {}", idx); | ||
| logState(); | ||
| throw new RuntimeException("Test failed because a write got stuck", e); | ||
| } | ||
|
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| idx++; | ||
| if (MEMORY_POOL.needsCleaning()) | ||
| { | ||
| lastTimePoolNeededCleaning = System.nanoTime(); | ||
| } | ||
| else | ||
| { | ||
| updateMaxTimeSinceCleanup(); | ||
| } | ||
|
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| if (MEMORY_POOL.getNumPendingtasks() > 2) | ||
| { | ||
| logger.info("Flushes seem to be backing up, sleeping at iteration {} to slow down writes", idx); | ||
| logState(); | ||
| Thread.sleep(100); | ||
| } | ||
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| assertEquals("write blocked on allocation", 0, MEMORY_POOL.blockedOnAllocating.getCount()); | ||
| } | ||
| scheduledExecutor.shutdown(); | ||
| assertTrue(scheduledExecutor.awaitTermination(1, TimeUnit.MINUTES)); | ||
| successfulUserFlush(); | ||
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| // check the amount of memory used for the memtables is less than half of the limit | ||
| // it is expected that if this resource leaks then these assertions won't hold | ||
| assertTrue(MEMORY_POOL.onHeap.used() < 1_000_000); | ||
| assertTrue(MEMORY_POOL.offHeap.used() < 1_000_000); | ||
| // assert no memtables are stuck in a reclaiming state | ||
| assertEquals(0, MEMORY_POOL.onHeap.getReclaiming()); | ||
| assertEquals(0, MEMORY_POOL.offHeap.getReclaiming()); | ||
| // check that memtable cleanup is scheduled sufficiently often | ||
| assertTrue("memory pool did not clean for more than 10s: " + maxTimeSinceCleanup + " ms", maxTimeSinceCleanup < 10_000); | ||
| // and that there were no writes that actually got blocked due to memory pressure | ||
| assertEquals("write blocked on allocation", 0, MEMORY_POOL.blockedOnAllocating.getCount()); | ||
| } | ||
| finally | ||
| { | ||
| logger.info("The ultimate system state:"); | ||
| logState(); | ||
| // If the test managed to reproduce the problem then writing may be blocked now. | ||
| // This means that @After in CQLTester will hang. | ||
| // To prevent this let's unblock writes by running a successful flush, which will | ||
| // free the current memtable. | ||
| successfulUserFlush(); | ||
| } | ||
| } | ||
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| private void updateMaxTimeSinceCleanup() | ||
| { | ||
| maxTimeSinceCleanup = Math.max(maxTimeSinceCleanup, (System.nanoTime() - lastTimePoolNeededCleaning) / TimeUnit.MILLISECONDS.toNanos(1)); | ||
| } | ||
|
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| private void logState() | ||
| { | ||
| logger.info(" --- STATE ---\n" + | ||
| "Max time since pool needed cleaning: {} ms\n" + | ||
| "Num failed flushes: {}\n" + | ||
| "Memory pool: onHeap.used={} ({} %), onHeap.getReclaiming={} ({} %)\n" + | ||
| "Memory pool: offHeap.used={} ({} %), offHeap.getReclaiming={} ({} %)\n" + | ||
| "Total size of sstables: {} bytes\n" + | ||
| "Num blocked allocations: {}", | ||
| maxTimeSinceCleanup, | ||
| numFailedFlushes, | ||
| MEMORY_POOL.onHeap.used(), 100 * MEMORY_POOL.onHeap.usedRatio(), MEMORY_POOL.onHeap.getReclaiming(), 100 * MEMORY_POOL.onHeap.reclaimingRatio(), | ||
| MEMORY_POOL.offHeap.used(), 100 * MEMORY_POOL.offHeap.usedRatio(), MEMORY_POOL.offHeap.getReclaiming(), 100 * MEMORY_POOL.offHeap.reclaimingRatio(), | ||
| getCurrentColumnFamilyStore().getLiveSSTables().stream().mapToLong(SSTableReader::bytesOnDisk).sum(), | ||
| MEMORY_POOL.blockedOnAllocating.getCount()); | ||
| } | ||
|
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| private void maybeThrowWhenFlushAddsSSTables(INotification notification, Object sender) | ||
| { | ||
| logger.info("Consuming notification {}", notification); | ||
| if (notification instanceof SSTableAddingNotification) | ||
| { | ||
| SSTableAddingNotification addingNotification = (SSTableAddingNotification) notification; | ||
| if (addingNotification.operationType == OperationType.FLUSH && addingNotification.memtable().get().metadata().name.equals("failedflushtest") | ||
| && failFlushProbability.get() > Math.random()) | ||
| { | ||
| logger.info("Throwing exception for notification {}", notification); | ||
| numFailedFlushes.incrementAndGet(); | ||
| throw new RuntimeException("hey I just broke your flush, haven't I?"); | ||
| } | ||
| } | ||
| } | ||
|
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| private void successfulUserFlush() | ||
| { | ||
| ColumnFamilyStore cfs = getCurrentColumnFamilyStore(); | ||
| cfs.getAllMemtables().forEach(m -> logger.info("pre flush memtable: {}", m)); | ||
| logState(); | ||
| try | ||
| { | ||
| failFlushProbability.set(0.0); | ||
| getCurrentColumnFamilyStore().forceFlush(ColumnFamilyStore.FlushReason.UNIT_TESTS).get(); | ||
| failFlushProbability.set(FLUSH_FAILURE_PROBABILITY); | ||
| } | ||
| catch (InterruptedException | ExecutionException e) | ||
| { | ||
| throw new RuntimeException(e); | ||
| } | ||
| finally | ||
| { | ||
| cfs.getAllMemtables().forEach(m -> logger.info("post flush memtable: {}", m)); | ||
| logState(); | ||
| numUserFlushes.incrementAndGet(); | ||
| } | ||
| } | ||
| } |
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Overall, the patch seems reasonable to me. However, as you said, it is not precisely defined what should happen in case of failure in
replaceFlushed. To me, since we have no answer, perhaps the best way to deal with that would be to shutdown the node, and at the same time, make sure that the notification consumer implementation does not throw any exception. Otherwise - from the CNDB point of view - is a failure in notification consumer critical? Can we continue if it happens?