[ https://issues.apache.org/jira/browse/RATIS-2116?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Haibo Sun updated RATIS-2116: ----------------------------- Description: Using version 2.5.1, we have discovered that in some cases, the state synchronization of the follower will be permanently blocked. Scenario: When the task queue of the SegmentedRaftLogWorker is the pattern (WriteLog, WriteLog, ..., PurgeLog), the last WriteLog of RaftServerImpl.appendEntries does not immediately flush data and complete the result future, because there is a pending PurgeLog task in the queue. It enqueues the result future to be completed after the latter WriteLog flushes data. However, the "nioEventLoopGroup-3-1" thread is already blocked, and will not add new WriteLog to the task queue of SegmentedRaftLogWorker. This leads to a deadlock and causes the state synchronization to stop. I confirmed this by adding debug logs, detailed information is attached below. This issue can be easily reproduced by increasing the frequency of TakeSnapshot and PurgeLog operations. In addition, after checking the code in the master branch, this issue still exists. *jstack:* "nioEventLoopGroup-3-1" #58 prio=10 os_prio=0 tid=0x00007fc58400b800 nid=0x5493a waiting on condition [0x00007fc5b4f28000] java.lang.Thread.State: WAITING (parking) at sun.misc.Unsafe.park0(Native Method) - parking to wait for <0x00007fd86a4685e8> (a java.util.concurrent.CompletableFuture$Signaller) at sun.misc.Unsafe.park(Unsafe.java:1025) at java.util.concurrent.locks.LockSupport.park(LockSupport.java:176) at java.util.concurrent.CompletableFuture$Signaller.block(CompletableFuture.java:1693) at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3323) at java.util.concurrent.CompletableFuture.waitingGet(CompletableFuture.java:1729) at java.util.concurrent.CompletableFuture.join(CompletableFuture.java:1934) at org.apache.ratis.server.impl.RaftServerImpl.appendEntries(RaftServerImpl.java:1379) at org.apache.ratis.server.impl.RaftServerProxy.appendEntries(RaftServerProxy.java:649) at org.apache.ratis.netty.server.NettyRpcService.handle(NettyRpcService.java:231) at org.apache.ratis.netty.server.NettyRpcService$InboundHandler.channelRead0(NettyRpcService.java:95) at org.apache.ratis.netty.server.NettyRpcService$InboundHandler.channelRead0(NettyRpcService.java:91) at org.apache.ratis.thirdparty.io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:99) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) at org.apache.ratis.thirdparty.io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:103) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) at org.apache.ratis.thirdparty.io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:346) at org.apache.ratis.thirdparty.io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:318) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) at org.apache.ratis.thirdparty.io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:440) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) at org.apache.ratis.thirdparty.io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919) at org.apache.ratis.thirdparty.io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:166) at org.apache.ratis.thirdparty.io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:788) at org.apache.ratis.thirdparty.io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:724) at org.apache.ratis.thirdparty.io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:650) at org.apache.ratis.thirdparty.io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:562) at org.apache.ratis.thirdparty.io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:997) at org.apache.ratis.thirdparty.io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) at org.apache.ratis.thirdparty.io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) at java.lang.Thread.run(Thread.java:882) *The debug logs which confirmed the cause:* 2024-06-23 11:44:08,881 [1@group-47BEDE733167-StateMachineUpdater] INFO raftlog.RaftLog - 1@group-47BEDE733167-SegmentedRaftLog: snapshotIndex: updateIncreasingly 17818160 -> 17868160 2024-06-23 11:44:08,881 [1@group-47BEDE733167-StateMachineUpdater] DEBUG raftlog.RaftLog - purging segments:toTruncate: null toDelete: [(17817216, 17818372) isOpen? false, length=0, newEndIndex=0, (17818373, 17819224) isOpen? false, length=0, newEndIndex=0, (17819225, 17820474) isOpen? false, length=0, newEndIndex=0, (17820475, 17821368) isOpen? false, length=0, newEndIndex=0, (17821369, 17822360) isOpen? false, length=0, newEndIndex=0, (17822361, 17823347) isOpen? false, length=0, newEndIndex=0, (17823348, 17824136) isOpen? false, length=0, newEndIndex=0, (17824137, 17825440) isOpen? false, length=0, newEndIndex=0, (17825441, 17826153) isOpen? false, length=0, newEndIndex=0, (17826154, 17826936) isOpen? false, length=0, newEndIndex=0, (17826937, 17827393) isOpen? false, length=0, newEndIndex=0, (17827394, 17828569) isOpen? false, length=0, newEndIndex=0, (17828570, 17829095) isOpen? false, length=0, newEndIndex=0, (17829096, 17830279) isOpen? false, length=0, newEndIndex=0, (17830280, 17831209) isOpen? false, length=0, newEndIndex=0, (17831210, 17831887) isOpen? false, length=0, newEndIndex=0, (17831888, 17832491) isOpen? false, length=0, newEndIndex=0, (17832492, 17833577) isOpen? false, length=0, newEndIndex=0, (17833578, 17834387) isOpen? false, length=0, newEndIndex=0, (17834388, 17835369) isOpen? false, length=0, newEndIndex=0, (17835370, 17836107) isOpen? false, length=0, newEndIndex=0, (17836108, 17837307) isOpen? false, length=0, newEndIndex=0, (17837308, 17838140) isOpen? false, length=0, newEndIndex=0, (17838141, 17838591) isOpen? false, length=0, newEndIndex=0, (17838592, 17839411) isOpen? false, length=0, newEndIndex=0, (17839412, 17840613) isOpen? false, length=0, newEndIndex=0, (17840614, 17841672) isOpen? false, length=0, newEndIndex=0, (17841673, 17842917) isOpen? false, length=0, newEndIndex=0, (17842918, 17843636) isOpen? false, length=0, newEndIndex=0, (17843637, 17844560) isOpen? false, length=0, newEndIndex=0, (17844561, 17847272) isOpen? false, length=0, newEndIndex=0, (17847273, 17847746) isOpen? false, length=0, newEndIndex=0, (17847747, 17848169) isOpen? false, length=0, newEndIndex=0, (17848170, 17848631) isOpen? false, length=0, newEndIndex=0, (17848632, 17849078) isOpen? false, length=0, newEndIndex=0, (17849079, 17850026) isOpen? false, length=0, newEndIndex=0, (17850027, 17850490) isOpen? false, length=0, newEndIndex=0, (17850491, 17851382) isOpen? false, length=0, newEndIndex=0, (17851383, 17852289) isOpen? false, length=0, newEndIndex=0, (17852290, 17853645) isOpen? false, length=0, newEndIndex=0, (17853646, 17854151) isOpen? false, length=0, newEndIndex=0, (17854152, 17855586) isOpen? false, length=0, newEndIndex=0, (17855587, 17856772) isOpen? false, length=0, newEndIndex=0, (17856773, 17857571) isOpen? false, length=0, newEndIndex=0, (17857572, 17858043) isOpen? false, length=0, newEndIndex=0, (17858044, 17858598) isOpen? false, length=0, newEndIndex=0, (17858599, 17859922) isOpen? false, length=0, newEndIndex=0, (17859923, 17860327) isOpen? false, length=0, newEndIndex=0, (17860328, 17861304) isOpen? false, length=0, newEndIndex=0, (17861305, 17862381) isOpen? false, length=0, newEndIndex=0, (17862382, 17863572) isOpen? false, length=0, newEndIndex=0, (17863573, 17864018) isOpen? false, length=0, newEndIndex=0, (17864019, 17865114) isOpen? false, length=0, newEndIndex=0, (17865115, 17866739) isOpen? false, length=0, newEndIndex=0, (17866740, 17867551) isOpen? false, length=0, newEndIndex=0] 2024-06-23 11:44:08,881 [1@group-47BEDE733167-StateMachineUpdater] DEBUG segmented.SegmentedRaftLogWorker - 1@group-47BEDE733167-SegmentedRaftLogWorker adds IO task PurgeLog:17867551 2024-06-23 11:44:08,881 [1@group-47BEDE733167-StateMachineUpdater] DEBUG segmented.SegmentedRaftLogWorker - added IO task (queueSize: 5) PurgeLog:17867551 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG raftlog.RaftLog - complete future of IO task WriteLog:17876749 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - done IO task WriteLog:17876749 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - dequeued IO task (index: 0, queueSize: 4) WriteLog:17876750 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - offer future of IO task WriteLog:17876750 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - done IO task WriteLog:17876750 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - dequeued IO task (index: 0, queueSize: 3) WriteLog:17876751 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - offer future of IO task WriteLog:17876751 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - done IO task WriteLog:17876751 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - dequeued IO task (index: 0, queueSize: 2) WriteLog:17876752 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - offer future of IO task WriteLog:17876752 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - done IO task WriteLog:17876752 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - dequeued IO task (index: 0, queueSize: 1) WriteLog:17876753 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - offer future of IO task WriteLog:17876753 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - done IO task WriteLog:17876753 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - dequeued IO task (index: 0, queueSize: 0) PurgeLog:17867551 2024-06-23 11:44:08,904 [1@group-47BEDE733167-SegmentedRaftLogWorker] INFO raftlog.RaftLog - 1@group-47BEDE733167-SegmentedRaftLog: purgeIndex: updateToMax old=17817215, new=17867551, updated? true 2024-06-23 11:44:08,904 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG raftlog.RaftLog - complete future of IO task PurgeLog:17867551 2024-06-23 11:44:08,904 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - done IO task PurgeLog:17867551 was: Using version 2.5.1, we have discovered that in some cases, the state synchronization of the follower will be permanently blocked. Scenario: When the task queue of the SegmentedRaftLogWorker is the pattern (WriteLog, WriteLog, ..., PurgeLog), the last WriteLog of RaftServerImpl.appendEntries does not immediately flush data and complete the result future, because there is a pending PurgeLog task in the queue. It enqueues the result future to be completed after the latter WriteLog flushes data. However, the "nioEventLoopGroup-3-1" thread is already blocked, and will not add new WriteLog to the task queue of SegmentedRaftLogWorker. This leads to a deadlock and causes the state synchronization to stop. I confirmed this by adding debug logs, detailed information is attached below. This issue can be easily reproduced by increasing the frequency of TakeSnapshot and PurgeLog operations. In addition, after checking the code in the master branch, this issue still exists. *jstack:* "nioEventLoopGroup-3-1" #58 prio=10 os_prio=0 tid=0x00007fc58400b800 nid=0x5493a waiting on condition [0x00007fc5b4f28000] java.lang.Thread.State: WAITING (parking) at sun.misc.Unsafe.park0(Native Method) - parking to wait for <0x00007fd86a4685e8> (a java.util.concurrent.CompletableFuture$Signaller) at sun.misc.Unsafe.park(Unsafe.java:1025) at java.util.concurrent.locks.LockSupport.park(LockSupport.java:176) at java.util.concurrent.CompletableFuture$Signaller.block(CompletableFuture.java:1693) at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3323) at java.util.concurrent.CompletableFuture.waitingGet(CompletableFuture.java:1729) at java.util.concurrent.CompletableFuture.join(CompletableFuture.java:1934) at org.apache.ratis.server.impl.RaftServerImpl.appendEntries(RaftServerImpl.java:1379) at org.apache.ratis.server.impl.RaftServerProxy.appendEntries(RaftServerProxy.java:649) at org.apache.ratis.netty.server.NettyRpcService.handle(NettyRpcService.java:231) at org.apache.ratis.netty.server.NettyRpcService$InboundHandler.channelRead0(NettyRpcService.java:95) at org.apache.ratis.netty.server.NettyRpcService$InboundHandler.channelRead0(NettyRpcService.java:91) at org.apache.ratis.thirdparty.io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:99) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) at org.apache.ratis.thirdparty.io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:103) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) at org.apache.ratis.thirdparty.io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:346) at org.apache.ratis.thirdparty.io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:318) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) at org.apache.ratis.thirdparty.io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:440) at org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) at org.apache.ratis.thirdparty.io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919) at org.apache.ratis.thirdparty.io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:166) at org.apache.ratis.thirdparty.io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:788) at org.apache.ratis.thirdparty.io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:724) at org.apache.ratis.thirdparty.io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:650) at org.apache.ratis.thirdparty.io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:562) at org.apache.ratis.thirdparty.io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:997) at org.apache.ratis.thirdparty.io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) at org.apache.ratis.thirdparty.io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) at java.lang.Thread.run(Thread.java:882) *The debug logs which confirmed the cause:* 2024-06-23 11:44:08,881 [1@group-47BEDE733167-StateMachineUpdater] INFO raftlog.RaftLog - 1@group-47BEDE733167-SegmentedRaftLog: snapshotIndex: updateIncreasingly 17818160 -> 17868160 2024-06-23 11:44:08,881 [1@group-47BEDE733167-StateMachineUpdater] DEBUG raftlog.RaftLog - purging segments:toTruncate: null toDelete: [(17817216, 17818372) isOpen? false, length=0, newEndIndex=0, (17818373, 17819224) isOpen? false, length=0, newEndIndex=0, (17819225, 17820474) isOpen? false, length=0, newEndIndex=0, (17820475, 17821368) isOpen? false, length=0, newEndIndex=0, (17821369, 17822360) isOpen? false, length=0, newEndIndex=0, (17822361, 17823347) isOpen? false, length=0, newEndIndex=0, (17823348, 17824136) isOpen? false, length=0, newEndIndex=0, (17824137, 17825440) isOpen? false, length=0, newEndIndex=0, (17825441, 17826153) isOpen? false, length=0, newEndIndex=0, (17826154, 17826936) isOpen? false, length=0, newEndIndex=0, (17826937, 17827393) isOpen? false, length=0, newEndIndex=0, (17827394, 17828569) isOpen? false, length=0, newEndIndex=0, (17828570, 17829095) isOpen? false, length=0, newEndIndex=0, (17829096, 17830279) isOpen? false, length=0, newEndIndex=0, (17830280, 17831209) isOpen? false, length=0, newEndIndex=0, (17831210, 17831887) isOpen? false, length=0, newEndIndex=0, (17831888, 17832491) isOpen? false, length=0, newEndIndex=0, (17832492, 17833577) isOpen? false, length=0, newEndIndex=0, (17833578, 17834387) isOpen? false, length=0, newEndIndex=0, (17834388, 17835369) isOpen? false, length=0, newEndIndex=0, (17835370, 17836107) isOpen? false, length=0, newEndIndex=0, (17836108, 17837307) isOpen? false, length=0, newEndIndex=0, (17837308, 17838140) isOpen? false, length=0, newEndIndex=0, (17838141, 17838591) isOpen? false, length=0, newEndIndex=0, (17838592, 17839411) isOpen? false, length=0, newEndIndex=0, (17839412, 17840613) isOpen? false, length=0, newEndIndex=0, (17840614, 17841672) isOpen? false, length=0, newEndIndex=0, (17841673, 17842917) isOpen? false, length=0, newEndIndex=0, (17842918, 17843636) isOpen? false, length=0, newEndIndex=0, (17843637, 17844560) isOpen? false, length=0, newEndIndex=0, (17844561, 17847272) isOpen? false, length=0, newEndIndex=0, (17847273, 17847746) isOpen? false, length=0, newEndIndex=0, (17847747, 17848169) isOpen? false, length=0, newEndIndex=0, (17848170, 17848631) isOpen? false, length=0, newEndIndex=0, (17848632, 17849078) isOpen? false, length=0, newEndIndex=0, (17849079, 17850026) isOpen? false, length=0, newEndIndex=0, (17850027, 17850490) isOpen? false, length=0, newEndIndex=0, (17850491, 17851382) isOpen? false, length=0, newEndIndex=0, (17851383, 17852289) isOpen? false, length=0, newEndIndex=0, (17852290, 17853645) isOpen? false, length=0, newEndIndex=0, (17853646, 17854151) isOpen? false, length=0, newEndIndex=0, (17854152, 17855586) isOpen? false, length=0, newEndIndex=0, (17855587, 17856772) isOpen? false, length=0, newEndIndex=0, (17856773, 17857571) isOpen? false, length=0, newEndIndex=0, (17857572, 17858043) isOpen? false, length=0, newEndIndex=0, (17858044, 17858598) isOpen? false, length=0, newEndIndex=0, (17858599, 17859922) isOpen? false, length=0, newEndIndex=0, (17859923, 17860327) isOpen? false, length=0, newEndIndex=0, (17860328, 17861304) isOpen? false, length=0, newEndIndex=0, (17861305, 17862381) isOpen? false, length=0, newEndIndex=0, (17862382, 17863572) isOpen? false, length=0, newEndIndex=0, (17863573, 17864018) isOpen? false, length=0, newEndIndex=0, (17864019, 17865114) isOpen? false, length=0, newEndIndex=0, (17865115, 17866739) isOpen? false, length=0, newEndIndex=0, (17866740, 17867551) isOpen? false, length=0, newEndIndex=0] 2024-06-23 11:44:08,881 [1@group-47BEDE733167-StateMachineUpdater] DEBUG segmented.SegmentedRaftLogWorker - 1@group-47BEDE733167-SegmentedRaftLogWorker adds IO task PurgeLog:17867551 2024-06-23 11:44:08,881 [1@group-47BEDE733167-StateMachineUpdater] DEBUG segmented.SegmentedRaftLogWorker - added IO task (queueSize: 5) PurgeLog:17867551 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG raftlog.RaftLog - complete future of IO task WriteLog:17876749 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - done IO task WriteLog:17876749 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - dequeued IO task (index: 0, queueSize: 4) WriteLog:17876750 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - offer future of IO task WriteLog:17876750 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - done IO task WriteLog:17876750 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - dequeued IO task (index: 0, queueSize: 3) WriteLog:17876751 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - offer future of IO task WriteLog:17876751 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - done IO task WriteLog:17876751 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - dequeued IO task (index: 0, queueSize: 2) WriteLog:17876752 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - offer future of IO task WriteLog:17876752 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - done IO task WriteLog:17876752 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - dequeued IO task (index: 0, queueSize: 1) WriteLog:17876753 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - offer future of IO task WriteLog:17876753 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - done IO task WriteLog:17876753 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - dequeued IO task (index: 0, queueSize: 0) PurgeLog:17867551 2024-06-23 11:44:08,904 [1@group-47BEDE733167-SegmentedRaftLogWorker] INFO raftlog.RaftLog - 1@group-47BEDE733167-SegmentedRaftLog: purgeIndex: updateToMax old=17817215, new=17867551, updated? true 2024-06-23 11:44:08,904 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG raftlog.RaftLog - complete future of IO task PurgeLog:17867551 2024-06-23 11:44:08,904 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG segmented.SegmentedRaftLogWorker - done IO task PurgeLog:17867551 > Follower state synchronization is blocked > ----------------------------------------- > > Key: RATIS-2116 > URL: https://issues.apache.org/jira/browse/RATIS-2116 > Project: Ratis > Issue Type: Bug > Affects Versions: 3.0.0, 2.5.1, 3.0.1 > Reporter: Haibo Sun > Priority: Major > > Using version 2.5.1, we have discovered that in some cases, the state > synchronization of the follower will be permanently blocked. > Scenario: When the task queue of the SegmentedRaftLogWorker is the pattern > (WriteLog, WriteLog, ..., PurgeLog), the last WriteLog of > RaftServerImpl.appendEntries does not immediately flush data and complete the > result future, because there is a pending PurgeLog task in the queue. It > enqueues the result future to be completed after the latter WriteLog flushes > data. However, the "nioEventLoopGroup-3-1" thread is already blocked, and > will not add new WriteLog to the task queue of SegmentedRaftLogWorker. This > leads to a deadlock and causes the state synchronization to stop. > I confirmed this by adding debug logs, detailed information is attached > below. This issue can be easily reproduced by increasing the frequency of > TakeSnapshot and PurgeLog operations. In addition, after checking the code in > the master branch, this issue still exists. > > *jstack:* > "nioEventLoopGroup-3-1" #58 prio=10 os_prio=0 tid=0x00007fc58400b800 > nid=0x5493a waiting on condition [0x00007fc5b4f28000] > java.lang.Thread.State: WAITING (parking) > at sun.misc.Unsafe.park0(Native Method) > - parking to wait for <0x00007fd86a4685e8> (a > java.util.concurrent.CompletableFuture$Signaller) > at sun.misc.Unsafe.park(Unsafe.java:1025) > at java.util.concurrent.locks.LockSupport.park(LockSupport.java:176) > at > java.util.concurrent.CompletableFuture$Signaller.block(CompletableFuture.java:1693) > at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3323) > at > java.util.concurrent.CompletableFuture.waitingGet(CompletableFuture.java:1729) > at java.util.concurrent.CompletableFuture.join(CompletableFuture.java:1934) > at > org.apache.ratis.server.impl.RaftServerImpl.appendEntries(RaftServerImpl.java:1379) > at > org.apache.ratis.server.impl.RaftServerProxy.appendEntries(RaftServerProxy.java:649) > at > org.apache.ratis.netty.server.NettyRpcService.handle(NettyRpcService.java:231) > at > org.apache.ratis.netty.server.NettyRpcService$InboundHandler.channelRead0(NettyRpcService.java:95) > at > org.apache.ratis.netty.server.NettyRpcService$InboundHandler.channelRead0(NettyRpcService.java:91) > at > org.apache.ratis.thirdparty.io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:99) > at > org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444) > at > org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) > at > org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) > at > org.apache.ratis.thirdparty.io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:103) > at > org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444) > at > org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) > at > org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) > at > org.apache.ratis.thirdparty.io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:346) > at > org.apache.ratis.thirdparty.io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:318) > at > org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444) > at > org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) > at > org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) > at > org.apache.ratis.thirdparty.io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410) > at > org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:440) > at > org.apache.ratis.thirdparty.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) > at > org.apache.ratis.thirdparty.io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919) > at > org.apache.ratis.thirdparty.io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:166) > at > org.apache.ratis.thirdparty.io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:788) > at > org.apache.ratis.thirdparty.io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:724) > at > org.apache.ratis.thirdparty.io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:650) > at > org.apache.ratis.thirdparty.io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:562) > at > org.apache.ratis.thirdparty.io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:997) > at > org.apache.ratis.thirdparty.io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) > at > org.apache.ratis.thirdparty.io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) > at java.lang.Thread.run(Thread.java:882) > > *The debug logs which confirmed the cause:* > 2024-06-23 11:44:08,881 [1@group-47BEDE733167-StateMachineUpdater] INFO > raftlog.RaftLog - 1@group-47BEDE733167-SegmentedRaftLog: snapshotIndex: > updateIncreasingly 17818160 -> 17868160 > 2024-06-23 11:44:08,881 [1@group-47BEDE733167-StateMachineUpdater] DEBUG > raftlog.RaftLog - purging segments:toTruncate: null > toDelete: [(17817216, 17818372) isOpen? false, length=0, newEndIndex=0, > (17818373, 17819224) isOpen? false, length=0, newEndIndex=0, (17819225, > 17820474) isOpen? false, length=0, newEndIndex=0, (17820475, 17821368) > isOpen? false, length=0, newEndIndex=0, (17821369, 17822360) isOpen? false, > length=0, newEndIndex=0, (17822361, 17823347) isOpen? false, length=0, > newEndIndex=0, (17823348, 17824136) isOpen? false, length=0, newEndIndex=0, > (17824137, 17825440) isOpen? false, length=0, newEndIndex=0, (17825441, > 17826153) isOpen? false, length=0, newEndIndex=0, (17826154, 17826936) > isOpen? false, length=0, newEndIndex=0, (17826937, 17827393) isOpen? false, > length=0, newEndIndex=0, (17827394, 17828569) isOpen? false, length=0, > newEndIndex=0, (17828570, 17829095) isOpen? false, length=0, newEndIndex=0, > (17829096, 17830279) isOpen? false, length=0, newEndIndex=0, (17830280, > 17831209) isOpen? false, length=0, newEndIndex=0, (17831210, 17831887) > isOpen? false, length=0, newEndIndex=0, (17831888, 17832491) isOpen? false, > length=0, newEndIndex=0, (17832492, 17833577) isOpen? false, length=0, > newEndIndex=0, (17833578, 17834387) isOpen? false, length=0, newEndIndex=0, > (17834388, 17835369) isOpen? false, length=0, newEndIndex=0, (17835370, > 17836107) isOpen? false, length=0, newEndIndex=0, (17836108, 17837307) > isOpen? false, length=0, newEndIndex=0, (17837308, 17838140) isOpen? false, > length=0, newEndIndex=0, (17838141, 17838591) isOpen? false, length=0, > newEndIndex=0, (17838592, 17839411) isOpen? false, length=0, newEndIndex=0, > (17839412, 17840613) isOpen? false, length=0, newEndIndex=0, (17840614, > 17841672) isOpen? false, length=0, newEndIndex=0, (17841673, 17842917) > isOpen? false, length=0, newEndIndex=0, (17842918, 17843636) isOpen? false, > length=0, newEndIndex=0, (17843637, 17844560) isOpen? false, length=0, > newEndIndex=0, (17844561, 17847272) isOpen? false, length=0, newEndIndex=0, > (17847273, 17847746) isOpen? false, length=0, newEndIndex=0, (17847747, > 17848169) isOpen? false, length=0, newEndIndex=0, (17848170, 17848631) > isOpen? false, length=0, newEndIndex=0, (17848632, 17849078) isOpen? false, > length=0, newEndIndex=0, (17849079, 17850026) isOpen? false, length=0, > newEndIndex=0, (17850027, 17850490) isOpen? false, length=0, newEndIndex=0, > (17850491, 17851382) isOpen? false, length=0, newEndIndex=0, (17851383, > 17852289) isOpen? false, length=0, newEndIndex=0, (17852290, 17853645) > isOpen? false, length=0, newEndIndex=0, (17853646, 17854151) isOpen? false, > length=0, newEndIndex=0, (17854152, 17855586) isOpen? false, length=0, > newEndIndex=0, (17855587, 17856772) isOpen? false, length=0, newEndIndex=0, > (17856773, 17857571) isOpen? false, length=0, newEndIndex=0, (17857572, > 17858043) isOpen? false, length=0, newEndIndex=0, (17858044, 17858598) > isOpen? false, length=0, newEndIndex=0, (17858599, 17859922) isOpen? false, > length=0, newEndIndex=0, (17859923, 17860327) isOpen? false, length=0, > newEndIndex=0, (17860328, 17861304) isOpen? false, length=0, newEndIndex=0, > (17861305, 17862381) isOpen? false, length=0, newEndIndex=0, (17862382, > 17863572) isOpen? false, length=0, newEndIndex=0, (17863573, 17864018) > isOpen? false, length=0, newEndIndex=0, (17864019, 17865114) isOpen? false, > length=0, newEndIndex=0, (17865115, 17866739) isOpen? false, length=0, > newEndIndex=0, (17866740, 17867551) isOpen? false, length=0, newEndIndex=0] > 2024-06-23 11:44:08,881 [1@group-47BEDE733167-StateMachineUpdater] DEBUG > segmented.SegmentedRaftLogWorker - > 1@group-47BEDE733167-SegmentedRaftLogWorker adds IO task PurgeLog:17867551 > 2024-06-23 11:44:08,881 [1@group-47BEDE733167-StateMachineUpdater] DEBUG > segmented.SegmentedRaftLogWorker - added IO task (queueSize: 5) > PurgeLog:17867551 > 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG > raftlog.RaftLog - complete future of IO task WriteLog:17876749 > 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG > segmented.SegmentedRaftLogWorker - done IO task WriteLog:17876749 > 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG > segmented.SegmentedRaftLogWorker - dequeued IO task (index: 0, queueSize: 4) > WriteLog:17876750 > 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG > segmented.SegmentedRaftLogWorker - offer future of IO task WriteLog:17876750 > 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG > segmented.SegmentedRaftLogWorker - done IO task WriteLog:17876750 > 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG > segmented.SegmentedRaftLogWorker - dequeued IO task (index: 0, queueSize: 3) > WriteLog:17876751 > 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG > segmented.SegmentedRaftLogWorker - offer future of IO task WriteLog:17876751 > 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG > segmented.SegmentedRaftLogWorker - done IO task WriteLog:17876751 > 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG > segmented.SegmentedRaftLogWorker - dequeued IO task (index: 0, queueSize: 2) > WriteLog:17876752 > 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG > segmented.SegmentedRaftLogWorker - offer future of IO task WriteLog:17876752 > 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG > segmented.SegmentedRaftLogWorker - done IO task WriteLog:17876752 > 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG > segmented.SegmentedRaftLogWorker - dequeued IO task (index: 0, queueSize: 1) > WriteLog:17876753 > 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG > segmented.SegmentedRaftLogWorker - offer future of IO task WriteLog:17876753 > 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG > segmented.SegmentedRaftLogWorker - done IO task WriteLog:17876753 > 2024-06-23 11:44:08,881 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG > segmented.SegmentedRaftLogWorker - dequeued IO task (index: 0, queueSize: 0) > PurgeLog:17867551 > 2024-06-23 11:44:08,904 [1@group-47BEDE733167-SegmentedRaftLogWorker] INFO > raftlog.RaftLog - 1@group-47BEDE733167-SegmentedRaftLog: purgeIndex: > updateToMax old=17817215, new=17867551, updated? true > 2024-06-23 11:44:08,904 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG > raftlog.RaftLog - complete future of IO task PurgeLog:17867551 > 2024-06-23 11:44:08,904 [1@group-47BEDE733167-SegmentedRaftLogWorker] DEBUG > segmented.SegmentedRaftLogWorker - done IO task PurgeLog:17867551 -- This message was sent by Atlassian Jira (v8.20.10#820010)