aoli-al opened a new issue, #13593:
URL: https://github.com/apache/lucene/issues/13593
### Description
I saw a failure in the test `testMaxMergeCount` due to concurrency issues.
```
𞤃𞤮𞤪𞤧𞤮 19, 2024 12:08:03 𞤇𞤎
com.carrotsearch.randomizedtesting.RandomizedRunner$QueueUncaughtExceptionsHandler
uncaughtException
WARNING: Uncaught exception in thread: Thread[#25,Lucene Merge Thread
#2,5,TGRP-TestConcurrentMergeScheduler]
org.apache.lucene.index.MergePolicy$MergeException:
java.lang.RuntimeException: java.lang.AssertionError: count=2 vs maxMergeCount=1
at __randomizedtesting.SeedInfo.seed([852F062F4E7F50BA]:0)
at
org.apache.lucene.index.ConcurrentMergeScheduler.handleMergeException(ConcurrentMergeScheduler.java:774)
at
org.apache.lucene.index.ConcurrentMergeScheduler$MergeThread.run(ConcurrentMergeScheduler.java:766)
Caused by: java.lang.RuntimeException: java.lang.AssertionError: count=2 vs
maxMergeCount=1
at
org.apache.lucene.index.TestConcurrentMergeScheduler$3.doMerge(TestConcurrentMergeScheduler.java:372)
at
org.apache.lucene.index.ConcurrentMergeScheduler$MergeThread.run(ConcurrentMergeScheduler.java:739)
Caused by: java.lang.AssertionError: count=2 vs maxMergeCount=1
at org.junit.Assert.fail(Assert.java:89)
at org.junit.Assert.assertTrue(Assert.java:42)
at
org.apache.lucene.index.TestConcurrentMergeScheduler$3.doMerge(TestConcurrentMergeScheduler.java:347)
... 1 more
```
The root cause is that a race could happen in the merge method.
https://github.com/apache/lucene/blob/cc3b412183c7acbb4a6c498e9babffba4e7d1f28/lucene/core/src/java/org/apache/lucene/index/ConcurrentMergeScheduler.java#L569-L573
The method calls `maybeStall` to check if the merge should be stalled due to
the thread limit. However, the loop will break if
`mergeSource.hasPendingMerges()` returns false. So, a concurrency issue may
arise if `mergeSource` adds new pending merges after this method is evaluated.
This will allow `ConcurrentMergeScheduler` to create more merge threads than
specified.
https://github.com/apache/lucene/blob/cc3b412183c7acbb4a6c498e9babffba4e7d1f28/lucene/core/src/java/org/apache/lucene/index/ConcurrentMergeScheduler.java#L618
Here is the code to reproduce the failure:
```
diff --git
a/lucene/core/src/java/org/apache/lucene/index/ConcurrentMergeScheduler.java
b/lucene/core/src/java/org/apache/lucene/index/ConcurrentMergeScheduler.java
index d0e79375ea6..a479637155e 100644
---
a/lucene/core/src/java/org/apache/lucene/index/ConcurrentMergeScheduler.java
+++
b/lucene/core/src/java/org/apache/lucene/index/ConcurrentMergeScheduler.java
@@ -541,6 +541,7 @@ public class ConcurrentMergeScheduler extends
MergeScheduler {
}
}
+ public static boolean threadMergeIssued = false;
@Override
public synchronized void merge(MergeSource mergeSource, MergeTrigger
trigger) throws IOException {
@@ -562,6 +563,7 @@ public class ConcurrentMergeScheduler extends
MergeScheduler {
message(" index(source): " + mergeSource.toString());
}
+ boolean mergeThreadCreated = false;
// Iterate, pulling from the IndexWriter's queue of
// pending merges, until it's empty:
while (true) {
@@ -569,6 +571,13 @@ public class ConcurrentMergeScheduler extends
MergeScheduler {
if (maybeStall(mergeSource) == false) {
break;
}
+ if (Thread.currentThread().getName().contains("Merge Thread") &&
mergeThreadCreated) {
+ threadMergeIssued = true;
+ try {
+ Thread.sleep(1000);
+ } catch (Exception e) {
+ }
+ }
OneMerge merge = mergeSource.getNextMerge();
if (merge == null) {
@@ -591,6 +600,7 @@ public class ConcurrentMergeScheduler extends
MergeScheduler {
message(" launch new thread [" + newMergeThread.getName() +
"]");
}
+ mergeThreadCreated = true;
newMergeThread.start();
updateMergeThreads();
diff --git a/lucene/core/src/java/org/apache/lucene/index/IndexWriter.java
b/lucene/core/src/java/org/apache/lucene/index/IndexWriter.java
index 44d8bee8460..f83c4cac519 100644
--- a/lucene/core/src/java/org/apache/lucene/index/IndexWriter.java
+++ b/lucene/core/src/java/org/apache/lucene/index/IndexWriter.java
@@ -2305,10 +2305,25 @@ public class IndexWriter
maybeMerge(config.getMergePolicy(), MergeTrigger.EXPLICIT,
UNBOUNDED_MAX_MERGE_SEGMENTS);
}
+ int index = 0;
private final void maybeMerge(MergePolicy mergePolicy, MergeTrigger
trigger, int maxNumSegments)
throws IOException {
ensureOpen(false);
- if (updatePendingMerges(mergePolicy, trigger, maxNumSegments) != null) {
+ boolean shouldWait = false;
+ if (index == 1) {
+ while (!ConcurrentMergeScheduler.threadMergeIssued) {
+ Thread.yield();
+ shouldWait = true;
+ }
+ }
+ MergePolicy.MergeSpecification result =
updatePendingMerges(mergePolicy, trigger, maxNumSegments);
+ if (result != null) {
+ index = 1;
+ if (shouldWait) {
+ try {
+ Thread.sleep(50000);
+ } catch (Exception e) {}
+ }
executeMerge(trigger);
}
}
diff --git
a/lucene/core/src/test/org/apache/lucene/index/TestConcurrentMergeScheduler.java
b/lucene/core/src/test/org/apache/lucene/index/TestConcurrentMergeScheduler.java
index 5f85b5d3774..407e6f5f4bb 100644
---
a/lucene/core/src/test/org/apache/lucene/index/TestConcurrentMergeScheduler.java
+++
b/lucene/core/src/test/org/apache/lucene/index/TestConcurrentMergeScheduler.java
@@ -321,8 +321,8 @@ public class TestConcurrentMergeScheduler extends
LuceneTestCase {
IndexWriterConfig iwc =
new IndexWriterConfig(new
MockAnalyzer(random())).setCommitOnClose(false);
- final int maxMergeCount = TestUtil.nextInt(random(), 1, 5);
- final int maxMergeThreads = TestUtil.nextInt(random(), 1,
maxMergeCount);
+ final int maxMergeCount = 1;
+ final int maxMergeThreads = 1;
final CountDownLatch enoughMergesWaiting = new
CountDownLatch(maxMergeCount);
final AtomicInteger runningMergeCount = new AtomicInteger(0);
final AtomicBoolean failed = new AtomicBoolean();
@@ -331,6 +331,7 @@ public class TestConcurrentMergeScheduler extends
LuceneTestCase {
System.out.println(
"TEST: maxMergeCount=" + maxMergeCount + " maxMergeThreads=" +
maxMergeThreads);
}
+ int[] index = new int[] {0};
ConcurrentMergeScheduler cms =
new ConcurrentMergeScheduler() {
@@ -358,6 +359,9 @@ public class TestConcurrentMergeScheduler extends
LuceneTestCase {
// Then sleep a bit to give a chance for the bug
// (too many pending merges) to appear:
Thread.sleep(20);
+ if (Thread.currentThread().getName().contains("#1")) {
+ Thread.sleep(50000);
+ }
super.doMerge(mergeSource, merge);
} finally {
runningMergeCount.decrementAndGet();
@@ -381,17 +385,17 @@ public class TestConcurrentMergeScheduler extends
LuceneTestCase {
IndexWriter w = new IndexWriter(dir, iwc);
Document doc = new Document();
doc.add(newField("field", "field", TextField.TYPE_NOT_STORED));
- while (enoughMergesWaiting.getCount() != 0 && !failed.get()) {
+ while (true) {
for (int i = 0; i < 10; i++) {
w.addDocument(doc);
}
}
- try {
- w.commit();
- } finally {
- w.close();
- }
- dir.close();
+// try {
+// w.commit();
+// } finally {
+// w.close();
+// }
+// dir.close();
}
public void testSmallMergesDonNotGetThreads() throws IOException {
```
With the patch `TestConcurrentMergeScheduler#testMaxMergeCount` will raise
assertion failure.
### Version and environment details
Version: 33a4c1d8ef999902dacedde9c7f04a3c7e2e78c9
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