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https://issues.apache.org/jira/browse/HBASE-14498?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16769759#comment-16769759
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Sergey Shelukhin commented on HBASE-14498:
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This is actually a critical data loss issue, because if RS is network split
from ZK, master could see its znode expire and reassign the region.
We've just had a ZK outage (not network) and some RSes kept running for hours
without having a connection, and doing region stuff.
+1 on the patch for now, I will commit Monday if no objections. nit: should use
HConstants.DEFAULT_ZK_SESSION_TIMEOUT, not 90000.
I think this area needs to be hardened; if the server disconnects just before
ZK ping update that was somehow delayed for almost the whole session timeout,
and then waits 2/3rd of the timeout to abort, that means master has to wait
conntimeout + some time after the znode is gone before reassigning regions.
Also, I am not sure abort is good enough because it also takes time and may do
cleanup and such that affects region directories and WALs. Ideally the server
should kill -9 itself when losing the lock, or smth close enough.
Also, I wonder if we should use Curator; e.g. use a lock, with master trying to
steal all server locks - the server is dead as soon as the lock is stolen.
Although I guess there, SUSPENDED still needs to be handled in a similar way;
but at least I hope it sends LOST on the lack of connection. Also, it would
reduce HBase ZK code and benefit from Curator wisdom :)
I'll file a JIRA or two after this patch.
> Master stuck in infinite loop when all Zookeeper servers are unreachable
> ------------------------------------------------------------------------
>
> Key: HBASE-14498
> URL: https://issues.apache.org/jira/browse/HBASE-14498
> Project: HBase
> Issue Type: Bug
> Components: master
> Affects Versions: 1.5.0, 2.0.0
> Reporter: Y. SREENIVASULU REDDY
> Assignee: Pankaj Kumar
> Priority: Critical
> Fix For: 3.0.0
>
> Attachments: HBASE-14498-V2.patch, HBASE-14498-V3.patch,
> HBASE-14498-V4.patch, HBASE-14498-V5.patch, HBASE-14498-V6.patch,
> HBASE-14498-V6.patch, HBASE-14498-addendum.patch,
> HBASE-14498-branch-1.2.patch, HBASE-14498-branch-1.3-V2.patch,
> HBASE-14498-branch-1.3.patch, HBASE-14498-branch-1.4.patch,
> HBASE-14498-branch-1.patch, HBASE-14498.007.patch, HBASE-14498.008.patch,
> HBASE-14498.master.001.patch, HBASE-14498.master.002.patch, HBASE-14498.patch
>
>
> We met a weird scenario in our production environment.
> In a HA cluster,
> > Active Master (HM1) is not able to connect to any Zookeeper server (due to
> > N/w breakdown on master machine network with Zookeeper servers).
> {code}
> 2015-09-26 15:24:47,508 INFO
> [HM1-Host:16000.activeMasterManager-SendThread(ZK-Host:2181)]
> zookeeper.ClientCnxn: Client session timed out, have not heard from server in
> 33463ms for sessionid 0x104576b8dda0002, closing socket connection and
> attempting reconnect
> 2015-09-26 15:24:47,877 INFO
> [HM1-Host:16000.activeMasterManager-SendThread(ZK-Host1:2181)]
> client.FourLetterWordMain: connecting to ZK-Host1 2181
> 2015-09-26 15:24:48,236 INFO [main-SendThread(ZK-Host1:2181)]
> client.FourLetterWordMain: connecting to ZK-Host1 2181
> 2015-09-26 15:24:49,879 WARN
> [HM1-Host:16000.activeMasterManager-SendThread(ZK-Host1:2181)]
> zookeeper.ClientCnxn: Can not get the principle name from server ZK-Host1
> 2015-09-26 15:24:49,879 INFO
> [HM1-Host:16000.activeMasterManager-SendThread(ZK-Host1:2181)]
> zookeeper.ClientCnxn: Opening socket connection to server
> ZK-Host1/ZK-IP1:2181. Will not attempt to authenticate using SASL (unknown
> error)
> 2015-09-26 15:24:50,238 WARN [main-SendThread(ZK-Host1:2181)]
> zookeeper.ClientCnxn: Can not get the principle name from server ZK-Host1
> 2015-09-26 15:24:50,238 INFO [main-SendThread(ZK-Host1:2181)]
> zookeeper.ClientCnxn: Opening socket connection to server
> ZK-Host1/ZK-Host1:2181. Will not attempt to authenticate using SASL (unknown
> error)
> 2015-09-26 15:25:17,470 INFO [main-SendThread(ZK-Host1:2181)]
> zookeeper.ClientCnxn: Client session timed out, have not heard from server in
> 30023ms for sessionid 0x2045762cc710006, closing socket connection and
> attempting reconnect
> 2015-09-26 15:25:17,571 WARN [master/HM1-Host/HM1-IP:16000]
> zookeeper.RecoverableZooKeeper: Possibly transient ZooKeeper,
> quorum=ZK-Host:2181,ZK-Host1:2181,ZK-Host2:2181,
> exception=org.apache.zookeeper.KeeperException$ConnectionLossException:
> KeeperErrorCode = ConnectionLoss for /hbase/master
> 2015-09-26 15:25:17,872 INFO [main-SendThread(ZK-Host:2181)]
> client.FourLetterWordMain: connecting to ZK-Host 2181
> 2015-09-26 15:25:19,874 WARN [main-SendThread(ZK-Host:2181)]
> zookeeper.ClientCnxn: Can not get the principle name from server ZK-Host
> 2015-09-26 15:25:19,874 INFO [main-SendThread(ZK-Host:2181)]
> zookeeper.ClientCnxn: Opening socket connection to server ZK-Host/ZK-IP:2181.
> Will not attempt to authenticate using SASL (unknown error)
> {code}
> > Since HM1 was not able to connect to any ZK, so session timeout didnt
> > happen at Zookeeper server side and HM1 didnt abort.
> > On Zookeeper session timeout standby master (HM2) registered himself as an
> > active master.
> > HM2 is keep on waiting for region server to report him as part of active
> > master intialization.
> {noformat}
> 2015-09-26 15:24:44,928 | INFO | HM2-Host:21300.activeMasterManager | Waiting
> for region servers count to settle; currently checked in 0, slept for 0 ms,
> expecting minimum of 1, maximum of 2147483647, timeout of 4500 ms, interval
> of 1500 ms. |
> org.apache.hadoop.hbase.master.ServerManager.waitForRegionServers(ServerManager.java:1011)
> ---
> ---
> 2015-09-26 15:32:50,841 | INFO | HM2-Host:21300.activeMasterManager | Waiting
> for region servers count to settle; currently checked in 0, slept for 483913
> ms, expecting minimum of 1, maximum of 2147483647, timeout of 4500 ms,
> interval of 1500 ms. |
> org.apache.hadoop.hbase.master.ServerManager.waitForRegionServers(ServerManager.java:1011)
> {noformat}
> > At other end, region servers are reporting to HM1 on 3 sec interval. Here
> > region server retrieve master location from zookeeper only when they
> > couldn't connect to Master (ServiceException).
> Region Server will not report HM2 as per current design until unless HM1
> abort,so HM2 will exit(InitializationMonitor) and again wait for region
> servers in loop.
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