haridsv commented on PR #8116:
URL: https://github.com/apache/hbase/pull/8116#issuecomment-4314845890
@Apache9 **I gave your inputs to to Cursor and asked it further diagnose and
this is what it said:**
---
I concur with the contributor. The metrics deadlock is a real bug and
appears
to be the primary root cause. Here's why:
What bad-run2 actually shows — two distinct failures in sequence
First attempt (visible in the XML, starting at ~07:24:54):
- testRegionServerSessionExpired actually ran for 353 seconds and timed out
- The NameNode entered safe mode due to low disk space ("NameNode low on
available disk space. Already in safe mode." at line 645 of the output)
- Meta region got stuck in "opening" state for ~5 minutes (07:25:13 through
07:30:xx)
- The deadlock the contributor describes prevented meta from ever finishing
open
Retry attempt (visible in the .txt summary, starting at 07:36:54):
- Surefire retried the test class, but the static TEST_UTIL still has
clusterTestDir set from the first attempt
- setupClusterTestDir() is a no-op (returns early because clusterTestDir
!=
null)
- startMiniDFSCluster(2) at line 71 creates a new NameNode in the same
directory that still has stale data from the first attempt
- Result: InconsistentFSStateException — a secondary failure caused by the
failed first attempt not cleaning up
The deadlock explained
Two threads hold resources the other needs:
1. RS_OPEN_META thread (opening meta region): needs to register a metrics
source
AssignRegionHandler.process → HRegion.openHRegion → replayRecoveredEdits →
flushCache → StoreFileWriter.close → HFile.updateWriteLatency →
MetricsIO.getInstance → MetricsIOSourceImpl.<init> →
MetricsSystemImpl.register() ← BLOCKED (needs MetricsSystem lock)
2. HBase-Metrics2 thread (JmxCacheBuster stopping MetricsSystem): holds the
MetricsSystem lock, needs meta to be readable
JmxCacheBusterRunnable.run → MetricsSystemImpl.stop() → stopSources() →
MetricsSourceAdapter.stop() → getMBeanInfo() → updateJmxCache() →
getMetrics()
→
MetricsMasterSourceImpl.getMetrics → getRegionCounts() →
listTableDescriptors() →
isTablePresent() → reads meta table →
CompletableFuture.get() ← WAITING (meta region can't open)
Classic deadlock: Meta open needs the metrics lock. Metrics shutdown holds
the
lock and needs meta.
---
**I also asked it to propose a fix and got the below response:**
---
First run (deadline 17:22:56, starting ~17:17):
- Line 95: testRegionServerSessionExpired — timed out at 349s (meta stuck
opening due to deadlock)
- Lines 12845-12880: remaining 4 tests — all failed instantly (deadline
already exceeded)
- Line 12881: afterAll — timed out at 360s
Rerun (deadline 17:28:56, starting at 17:28:57):
- Line 12889: <rerunError> — beforeAll timed out →
InconsistentFSStateException
The output .txt file only contains the rerun's logs (starts at 17:28:57).
The
first run's logs are embedded in the XML's <system-err> CDATA section for
testRegionServerSessionExpired.
The pattern is identical in both bad-run and bad-run2: deadlock causes
timeout
in first run → stale state causes InconsistentFSStateException in rerun.
---
Proposed Fix for the Deadlock
The deadlock chain is:
1. RS_OPEN_META thread: opening meta → replay edits → flush →
HFile.updateWriteLatency() → MetricsIO.getInstance() →
BaseSourceImpl.<init> →
MetricsSystemImpl.register() → BLOCKED (MetricsSystem lock held by thread
2)
2. HBase-Metrics2 thread: JmxCacheBuster → MetricsSystemImpl.stop() → HOLDS
MetricsSystem lock → stopSources() → MetricsSourceAdapter.getMBeanInfo() →
updateJmxCache() → getMetrics() → MetricsMasterSourceImpl.getMetrics() →
MetricsMasterWrapperImpl.getRegionCounts() → master.listTableDescriptors()
→
tableStateManager.isTablePresent() → reads meta → WAITING (meta being
opened
by thread 1)
The best fix is Option A: make getRegionCounts() not read meta. The current
implementation calls master.listTableDescriptors() just to get the list of
tables, then calls the in-memory getRegionByStateOfTable() per table. But
listTableDescriptors() calls tableStateManager.isTablePresent() which does
a
synchronous meta read. This is unnecessary — the
AssignmentManager.RegionStates already has the full in-memory state:
```
⏺
Update(~/src/apache/hbase/hbase-server/src/main/java/org/apache/hadoop/hbase/m
aster/MetricsMasterWrapperImpl.java)
⎿ Added 11 lines, removed 18 lines
217
218 @Override
219 public PairOfSameType<Integer> getRegionCounts() {
220 - try {
221 - if (!master.isInitialized()) {
222 - return new PairOfSameType<>(0, 0);
223 - }
224 - Integer onlineRegionCount = 0;
225 - Integer offlineRegionCount = 0;
226 -
227 - List<TableDescriptor> descriptors = master.listTableDesc
-riptors(null, null, null, false);
228 -
229 - for (TableDescriptor htDesc : descriptors) {
230 - TableName tableName = htDesc.getTableName();
231 - Map<RegionState.State, List<RegionInfo>> tableRegions
-=
232 - master.getAssignmentManager().getRegionStates().getR
-egionByStateOfTable(tableName);
233 - onlineRegionCount += tableRegions.get(RegionState.Stat
-e.OPEN).size();
234 - offlineRegionCount += tableRegions.get(RegionState.Sta
-te.OFFLINE).size();
235 - }
236 - return new PairOfSameType<>(onlineRegionCount, offlineRe
-gionCount);
237 - } catch (IOException e) {
220 + if (!master.isInitialized() || master.getAssignmentManager
+() == null) {
221 return new PairOfSameType<>(0, 0);
222 }
223 + int onlineRegionCount = 0;
224 + int offlineRegionCount = 0;
225 + for (RegionState rs : master.getAssignmentManager().getReg
+ionStates().getRegionStates()) {
226 + if (rs.isOpened()) {
227 + onlineRegionCount++;
228 + } else if (rs.isOffline()) {
229 + offlineRegionCount++;
230 + }
231 + }
232 + return new PairOfSameType<>(onlineRegionCount, offlineRegi
+onCount);
233 }
234
235 @Override
```
⏺ Now let me verify the RegionState API has isOpened() and isOffline():
Searched for 1 pattern (ctrl+o to expand)
⏺ Let me also verify we still match the old semantics — the old code checked
OPEN and OFFLINE states:
Read 1 file (ctrl+o to expand)
⏺ Good, isOpened() checks State.OPEN and isOffline() checks State.OFFLINE —
same
states as the old code. Now let me clean up unused imports:
Read 1 file (ctrl+o to expand)
⏺ Let me check what's still used in the file:
Searched for 1 pattern (ctrl+o to expand)
⏺ Now let me check if IOException, List, RegionInfo, and TableDescriptor are
still used elsewhere in the file:
Searched for 2 patterns (ctrl+o to expand)
⏺ Good — IOException, RegionInfo, and TableDescriptor are no longer used.
Let me
also check List:
Searched for 1 pattern (ctrl+o to expand)
⏺ Let me clean up the unused imports and add the new one:
```
⏺
Update(~/src/apache/hbase/hbase-server/src/main/java/org/apache/hadoop/hbase/m
aster/MetricsMasterWrapperImpl.java)
⎿ Added 1 line, removed 4 lines
17 */
18 package org.apache.hadoop.hbase.master;
19
20 -import java.io.IOException;
20 import java.util.AbstractMap.SimpleImmutableEntry;
21 import java.util.Collections;
22 import java.util.HashMap;
24 -import java.util.List;
23 import java.util.Map;
24 import java.util.Map.Entry;
25 import org.apache.commons.lang3.StringUtils;
26 import org.apache.hadoop.hbase.ServerName;
27 import org.apache.hadoop.hbase.TableName;
30 -import org.apache.hadoop.hbase.client.RegionInfo;
31 -import org.apache.hadoop.hbase.client.TableDescriptor;
28 +import org.apache.hadoop.hbase.master.RegionState;
29 import org.apache.hadoop.hbase.quotas.QuotaObserverChore;
30 import org.apache.hadoop.hbase.quotas.SpaceQuotaSnapshot;
31 import org.apache.hadoop.hbase.util.PairOfSameType;
```
⏺ Let me verify the final state of the file:
Read 1 file (ctrl+o to expand)
⏺ Good. Now let me verify the compilation would work by checking that
RegionState is accessible from this package:
Searched for 1 pattern (ctrl+o to expand)
⏺ Let me verify the changes look complete:
```
⏺ Bash(cd /Users/hdara/src/apache/hbase && git diff --stat HEAD)
⎿ .../hbase/master/MetricsMasterWrapperImpl.java | 34 ++++++++-----
---------
1 file changed, 12 insertions(+), 22 deletions(-)
⎿ Shell cwd was reset to /Users/hdara/tmp/Debug-TestZooKeeper-Flapper
⏺ Bash(cd /Users/hdara/src/apache/hbase && git diff HEAD)
⎿ diff --git hbase-server/src/main/java/org/apache/hadoop/hbase/master/M
etricsMasterWrapperImpl.java hbase-server/src/main/java/org/apache/had
oop/hbase/master/MetricsMasterWrapperImpl.java
… +35 lines (ctrl+o to expand)
⎿ Shell cwd was reset to /Users/hdara/tmp/Debug-TestZooKeeper-Flapper
```
⏺ The fix looks clean. Let me summarize everything:
---
Summary
Two Runs Demarcation
Both bad-run and bad-run2 follow the same pattern. In the XML:
Column 1: bad-run
First Run: testRegionServerSessionExpired timed out (349s), deadline
17:22:56.
Remaining 4 tests failed instantly. Found in XML lines 95-12880.
Rerun: <rerunError> at XML line 12889: InconsistentFSStateException. Rerun
logs
in the .txt output file.
────────────────────────────────────────
Column 1: bad-run2
First Run: testRegionServerSessionExpired timed out (353s), deadline
07:30:54.
Found in XML line 95.
Rerun: InconsistentFSStateException in .txt summary. Rerun logs in the .txt
output file.
The first run's output logs are embedded in the XML's <system-err> CDATA
for
testRegionServerSessionExpired. The .txt output file only captures the
rerun.
Fix Applied
Changed MetricsMasterWrapperImpl.getRegionCounts() to use purely in-memory
RegionStates instead of calling master.listTableDescriptors() which reads
meta
via tableStateManager.isTablePresent().
Why this breaks the deadlock: The HBase-Metrics2 thread (JmxCacheBuster)
will
no longer attempt to read the meta table while holding the MetricsSystem
lock.
Since RegionStates.getRegionStates() iterates an in-memory
ConcurrentSkipListMap, it cannot block on meta availability, eliminating
the
circular dependency.
Semantic equivalence: The old code iterated tables from
listTableDescriptors()
and summed OPEN/OFFLINE counts per table. The new code iterates all
RegionState entries from the same in-memory regionsMap and counts the same
State.OPEN and State.OFFLINE states directly. The counts will be identical.
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