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Andrew Kyle Purtell commented on HBASE-25984: --------------------------------------------- PR is merged. What is the status of this JIRA? Backports in progress? > FSHLog WAL lockup with sync future reuse [RS deadlock] > ------------------------------------------------------ > > Key: HBASE-25984 > URL: https://issues.apache.org/jira/browse/HBASE-25984 > Project: HBase > Issue Type: Bug > Components: regionserver, wal > Affects Versions: 3.0.0-alpha-1, 1.7.0, 2.5.0, 2.4.5 > Reporter: Bharath Vissapragada > Assignee: Bharath Vissapragada > Priority: Critical > Labels: deadlock, hang > Attachments: HBASE-25984-unit-test.patch > > > We use FSHLog as the WAL implementation (branch-1 based) and under heavy load > we noticed the WAL system gets locked up due to a subtle bug involving racy > code with sync future reuse. This bug applies to all FSHLog implementations > across branches. > Symptoms: > On heavily loaded clusters with large write load we noticed that the region > servers are hanging abruptly with filled up handler queues and stuck MVCC > indicating appends/syncs not making any progress. > {noformat} > WARN [8,queue=9,port=60020] regionserver.MultiVersionConcurrencyControl - > STUCK for : 296000 millis. > MultiVersionConcurrencyControl{readPoint=172383686, writePoint=172383690, > regionName=1ce4003ab60120057734ffe367667dca} > WARN [6,queue=2,port=60020] regionserver.MultiVersionConcurrencyControl - > STUCK for : 296000 millis. > MultiVersionConcurrencyControl{readPoint=171504376, writePoint=171504381, > regionName=7c441d7243f9f504194dae6bf2622631} > {noformat} > All the handlers are stuck waiting for the sync futures and timing out. > {noformat} > java.lang.Object.wait(Native Method) > > org.apache.hadoop.hbase.regionserver.wal.SyncFuture.get(SyncFuture.java:183) > > org.apache.hadoop.hbase.regionserver.wal.FSHLog.blockOnSync(FSHLog.java:1509) > ..... > {noformat} > Log rolling is stuck because it was unable to attain a safe point > {noformat} > java.util.concurrent.CountDownLatch.await(CountDownLatch.java:277) > org.apache.hadoop.hbase.regionserver.wal.FSHLog$SafePointZigZagLatch.waitSafePoint(FSHLog.java:1799) > > org.apache.hadoop.hbase.regionserver.wal.FSHLog.replaceWriter(FSHLog.java:900) > {noformat} > and the Ring buffer consumer thinks that there are some outstanding syncs > that need to finish.. > {noformat} > > org.apache.hadoop.hbase.regionserver.wal.FSHLog$RingBufferEventHandler.attainSafePoint(FSHLog.java:2031) > > org.apache.hadoop.hbase.regionserver.wal.FSHLog$RingBufferEventHandler.onEvent(FSHLog.java:1999) > > org.apache.hadoop.hbase.regionserver.wal.FSHLog$RingBufferEventHandler.onEvent(FSHLog.java:1857) > {noformat} > On the other hand, SyncRunner threads are idle and just waiting for work > implying that there are no pending SyncFutures that need to be run > {noformat} > sun.misc.Unsafe.park(Native Method) > java.util.concurrent.locks.LockSupport.park(LockSupport.java:175) > > java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039) > > java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442) > > org.apache.hadoop.hbase.regionserver.wal.FSHLog$SyncRunner.run(FSHLog.java:1297) > java.lang.Thread.run(Thread.java:748) > {noformat} > Overall the WAL system is dead locked and could make no progress until it was > aborted. I got to the bottom of this issue and have a patch that can fix it > (more details in the comments due to word limit in the description). -- This message was sent by Atlassian Jira (v8.3.4#803005)