Hi Aaron, some questions/comments below:

On 04/28/2010 06:29 PM, Aaron Crow wrote:
We were running version 3.2.2 for about a month and it was working well for
us. Then late this past Saturday night, our cluster went pathological. One
of the 3 ZK servers spewed many WARNs (see below), and the other 2 servers
were almost constantly pegging the CPU. All three servers are on separate
machines. From what we could tell, the machines were fine... networking
fine, disk fine, etc. The ZK clients were completely unable to complete
their connections to ZK.


These machines are local (not wan) connected then? What OS and java version are you using?

Do you see any FATAL or ERROR level messages in the logs?

It would help to look at your zk config files for these servers. Could you provide (you might want to create a JIRA first, then just attach configs and other details/collateral to that, easier than dealing with email)

If you have logs for the time period and can share that would be most useful. (again, gzip and attach to the jira)

We tried all sorts of restarts, running zkCleanup, etc. We even completely
shut down our clients... and the pathology continued. Our workaround was to
do an urgent upgrade to version 3.3.0. The new ZK cluster with 3.3.0 has
been running well for us... so far...


Off hand and with the data we have so far nothing sticks out that 3.3 would have resolved (JIRA is conveniently down for the last hour or so so I can't review right now). Although there were some changes to reduce memory consumption (see below).

I realize that, sadly, this message doesn't contain nearly enough details to
trace exactly what happened. I guess I'm wondering if anyone has seen this
general scenario, and/or knows how to prevent? Is there anything we might be
doing client side to trigger this? Our application level request frequency
is maybe a few requests to Zookeeper per second, times 5 clients
applications. If we detect a SESSION EXPIRED, we do a simple "create new
client and use that instead". And we were seeing this happen occasionally.


What are the client doing? Do you have a large number/size of znodes?

Do you see any OutOfMemoryError in the logs?

Could the ZK server java process be swapping? Are you monitoring GC, perhaps large GC pauses are happening?

I have a suspicion that one of a few things might be happening. I see the following in your original email:

> :followerhand...@302] - Sending snapshot last zxid of peer is 0xd0007d66d
> zxid of leader is 0xf00000000
> 2010-04-24 23:06:03,254 - ERROR [FollowerHandler-/10.0.10.116:34405
> :followerhand...@415] - Unexpected exception causing shutdown while sock
> still open
> java.net.SocketException: Broken pipe
>          at java.net.SocketOutputStream.socketWrite0(Native Method)
>          at

^^^^ this log section is saying that a ZK server (follower) connected to the elected leader and started to download (leader is sending here) the latest ZK snapshot (db) to the follower while it is recovering. However before the follower fully downloads the snapshot the connection (pipe) is broken and this operation fails. At this point the leader itself will probably give up the lead, a new election will happen, and it might be the case that this same problem occurs - the follower tries to download the snapshot but it again fails (and this loops forever)

This issue can happen if the servers are slowed, either by slow interconnects (wan), network connectivity/perf problems, swapping of the JVM, and most commonly GC in the VM.

See this recent case:
http://www.mail-archive.com/zookeeper-...@hadoop.apache.org/msg08083.html

What is the size of your snapshot file? (you can see this in your zookeeper datadirectory, unless you wiped this during your attempt to cleanup/recover/upgrade?).

Seeing your config file, and getting a sense of the snapshot file size will give us more insight.

Patrick

Many, many thanks in advance for any insights or advice.


Example log output from the ZK server that spewed many WARNs:

===

2010-04-24 22:31:24,551 - WARN
  [QuorumPeer:/0:0:0:0:0:0:0:0:2181:follo...@318] - Exception when following
the leader
java.net.SocketTimeoutException: Read timed out
at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.read(SocketInputStream.java:129)
at java.io.BufferedInputStream.fill(BufferedInputStream.java:218)
at java.io.BufferedInputStream.read(BufferedInputStream.java:237)
at java.io.DataInputStream.readInt(DataInputStream.java:370)
at org.apache.jute.BinaryInputArchive.readInt(BinaryInputArchive.java:63)
at
org.apache.zookeeper.server.quorum.QuorumPacket.deserialize(QuorumPacket.java:66)
at
org.apache.jute.BinaryInputArchive.readRecord(BinaryInputArchive.java:108)
at org.apache.zookeeper.server.quorum.Follower.readPacket(Follower.java:114)
at
org.apache.zookeeper.server.quorum.Follower.followLeader(Follower.java:193)
at org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:525)
2010-04-24 22:31:24,552 - INFO
  [QuorumPeer:/0:0:0:0:0:0:0:0:2181:follo...@436] - shutdown called
java.lang.Exception: shutdown Follower
at org.apache.zookeeper.server.quorum.Follower.shutdown(Follower.java:436)
at org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:529)
2010-04-24 22:31:24,552 - INFO
  [QuorumPeer:/0:0:0:0:0:0:0:0:2181:quorump...@514] - LOOKING

...

2010-04-24 22:31:27,257 - WARN  [NIOServerCxn.Factory:2181:nioserverc...@518]
- Exception causing close of session 0x0 due to java.io.IOException:
ZooKeeperServer not running
2010-04-24 22:31:27,257 - INFO  [NIOServerCxn.Factory:2181:nioserverc...@857]
- closing session:0x0 NIOServerCnxn:
java.nio.channels.SocketChannel[connected local=/127.0.0.1:2181remote=/
127.0.0.1:44589]
2010-04-24 22:31:27,705 - INFO
  [QuorumPeer:/0:0:0:0:0:0:0:0:2181:fastleaderelect...@706] - Notification:
3, 60129542145, 2, 1, LOOKING, LEADING, 3
2010-04-24 22:31:27,705 - INFO
  [QuorumPeer:/0:0:0:0:0:0:0:0:2181:quorump...@523] - FOLLOWING
2010-04-24 22:31:27,705 - INFO
  [QuorumPeer:/0:0:0:0:0:0:0:0:2181:zookeeperser...@160] - Created server
2010-04-24 22:31:27,706 - INFO
  [QuorumPeer:/0:0:0:0:0:0:0:0:2181:follo...@147] - Following sum08/
10.0.10.118:2888
2010-04-24 22:31:29,040 - WARN  [NIOServerCxn.Factory:2181:nioserverc...@518]
- Exception causing close of session 0x0 due to java.io.IOException:
ZooKeeperServer not running
2010-04-24 22:31:29,040 - INFO  [NIOServerCxn.Factory:2181:nioserverc...@857]
- closing session:0x0 NIOServerCnxn:
java.nio.channels.SocketChannel[connected local=/127.0.0.1:2181remote=/
127.0.0.1:44591]
2010-04-24 22:31:31,069 - WARN  [NIOServerCxn.Factory:2181:nioserverc...@518]
- Exception causing close of session 0x0 due to java.io.IOException:
ZooKeeperServer not running
2010-04-24 22:31:31,069 - INFO  [NIOServerCxn.Factory:2181:nioserverc...@857]
- closing session:0x0 NIOServerCnxn:
java.nio.channels.SocketChannel[connected local=/127.0.0.1:2181remote=/
127.0.0.1:44592]
2010-04-24 22:31:32,589 - WARN  [NIOServerCxn.Factory:2181:nioserverc...@518]
- Exception causing close of session 0x0 due to java.io.IOException:
ZooKeeperServer not running

===

Example log output from a server that was pegging CPU:

010-04-24 23:05:27,911 - INFO  [WorkerReceiver
Thread:fastleaderelection$messenger$workerrecei...@254] - Sending new
notification.
2010-04-24 23:05:27,912 - INFO  [WorkerReceiver
Thread:fastleaderelection$messenger$workerrecei...@254] - Sending new
notification.
2010-04-24 23:05:27,910 - WARN  [Thread-15:quorumcnxmanager$sendwor...@539]
- Interrupted while waiting for message on queue
java.lang.InterruptedException
         at
java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.reportInterruptAfterWait(AbstractQueuedSynchronizer.java:1899)
         at
java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1934)
         at
java.util.concurrent.ArrayBlockingQueue.take(ArrayBlockingQueue.java:317)
         at
org.apache.zookeeper.server.quorum.QuorumCnxManager$SendWorker.run(QuorumCnxManager.java:533)
2010-04-24 23:05:27,912 - INFO  [WorkerReceiver
Thread:fastleaderelection$messenger$workerrecei...@254] - Sending new
notification.
2010-04-24 23:05:27,912 - WARN  [Thread-16:quorumcnxmanager$recvwor...@623]
- Connection broken:
java.nio.channels.AsynchronousCloseException
         at
java.nio.channels.spi.AbstractInterruptibleChannel.end(AbstractInterruptibleChannel.java:185)
         at sun.nio.ch.SocketChannelImpl.read(SocketChannelImpl.java:263)
         at
org.apache.zookeeper.server.quorum.QuorumCnxManager$RecvWorker.run(QuorumCnxManager.java:594)
2010-04-24 23:05:27,912 - WARN  [Thread-15:quorumcnxmanager$sendwor...@554]
- Send worker leaving thread

...

010-04-24 23:05:51,952 - INFO  [WorkerReceiver
Thread:fastleaderelection$messenger$workerrecei...@254] - Sending new
notification.
2010-04-24 23:05:57,148 - INFO  [WorkerReceiver
Thread:fastleaderelection$messenger$workerrecei...@254] - Sending new
notification.
2010-04-24 23:06:03,243 - INFO  [FollowerHandler-/10.0.10.116:34405
:followerhand...@227] - Follower sid: 1 : info :
org.apache.zookeeper.server.quorum.quorumpeer$quorumser...@364641
2010-04-24 23:06:03,244 - WARN  [FollowerHandler-/10.0.10.116:34405
:followerhand...@302] - Sending snapshot last zxid of peer is 0xd0007d66d
zxid of leader is 0xf00000000
2010-04-24 23:06:03,254 - ERROR [FollowerHandler-/10.0.10.116:34405
:followerhand...@415] - Unexpected exception causing shutdown while sock
still open
java.net.SocketException: Broken pipe
         at java.net.SocketOutputStream.socketWrite0(Native Method)
         at
java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:92)
         at java.net.SocketOutputStream.write(SocketOutputStream.java:136)
         at
java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:65)
         at java.io.BufferedOutputStream.write(BufferedOutputStream.java:109)
         at java.io.DataOutputStream.writeLong(DataOutputStream.java:207)
         at
org.apache.jute.BinaryOutputArchive.writeLong(BinaryOutputArchive.java:59)
         at org.apache.zookeeper.server.DataNode.serialize(DataNode.java:129)
         at
org.apache.jute.BinaryOutputArchive.writeRecord(BinaryOutputArchive.java:123)
         at
org.apache.zookeeper.server.DataTree.serializeNode(DataTree.java:917)
         at
org.apache.zookeeper.server.DataTree.serializeNode(DataTree.java:929)
         at
org.apache.zookeeper.server.DataTree.serializeNode(DataTree.java:929)
         at
org.apache.zookeeper.server.DataTree.serializeNode(DataTree.java:929)
         at
org.apache.zookeeper.server.DataTree.serializeNode(DataTree.java:929)
         at org.apache.zookeeper.server.DataTree.serialize(DataTree.java:979)
         at
org.apache.zookeeper.server.util.SerializeUtils.serializeSnapshot(SerializeUtils.java:104)
         at
org.apache.zookeeper.server.ZooKeeperServer.serializeSnapshot(ZooKeeperServer.java:272)
         at
org.apache.zookeeper.server.quorum.FollowerHandler.run(FollowerHandler.java:307)
2010-04-24 23:06:03,255 - WARN  [FollowerHandler-/10.0.10.116:34405
:followerhand...@421] - ******* GOODBYE /10.0.10.116:34405 ********
2010-04-24 23:06:03,550 - INFO  [WorkerReceiver
Thread:fastleaderelection$messenger$workerrecei...@254] - Sending new
notification.

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