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From Jean-Daniel Cryans <jdcry...@apache.org>
Subject Re: Cannot locate root region
Date Fri, 29 Jan 2010 17:39:35 GMT
I just created https://issues.apache.org/jira/browse/HBASE-2174

We handle addresses in different ways depending on which part of the
code you're in. We should correct that everywhere by implementing a
solution that also solves what you guys are seeing.

J-D

On Fri, Jan 29, 2010 at 8:33 AM, Kannan Muthukkaruppan
<Kannan@facebook.com> wrote:
> @Joy: The info stored in .META. for various regions as well as in the ephemeral nodes
for region servers in zookeeper are both already IP address based. So doesn't look like multi-homing
and/or the other flexibilities you mention were a design goal as far as I can tell.
>
> Regarding: <<< doesn't the reverse ip lookup just once at RS startup time?>>>,
what seems to be happening is this:
>
> A regionServer periodically sends a regionServerReport (RPC call) to the master. A HServerInfo
argument is passed as an argument and it identifies the sending region server's identity in
IP address format.
>
> The master, in ServerManager class, maintains a serversToServerInfo map which is hostname
based. Every time a master receives a regionServerReport it converts the IP address based
name to a hostname via the info.getServerName() call. Normally this call returns the hostname,
but we suspect that during the DNS flakiness, it returned an IP address based string. And
so, this caused ServerManager.java to think that it was hearing from a new server. And this
lead to:
>
>  HServerInfo storedInfo = serversToServerInfo.get(info.getServerName());
>    if (storedInfo == null) {
>      if (LOG.isDebugEnabled()) {
>        LOG.debug("Received report from unknown server -- telling it " +   <<============
>          "to " + CALL_SERVER_STARTUP + ": " + info.getServerName());  <<============
>      }
>
> and bad things down the road.
>
> The above error message in our logs (example below) indeed identified the host in IP
address syntax, even though normally the getServerName call would return the info in hostname
format.
>
> 2010-01-28 11:21:34,539 DEBUG org.apache.hadoop.hbase.master.ServerManager: Received
report from unknown server -- telling it to MSG_CALL_SERVER_STARTUP: 10.129.68.203,60020,1263605543210
>
> This affected three of our test clusters at the same time!
>
> Perhaps all we need to do is to change the ServerManager's internal maps to all be IP
based? That way we avoid/bypass the master having to look up the hostname on every heartbeat.
>
> regards,
> Kannan
> ________________________________________
> From: Joydeep Sarma [jsensarma@gmail.com]
> Sent: Friday, January 29, 2010 1:20 AM
> To: hbase-dev@hadoop.apache.org
> Subject: Re: Cannot locate root region
>
> hadoop also uses the hostnames. if a host is multi-homed - it's
> hostname is a better identifier (which still allows it to use
> different nics/ips for actual traffic). it can help in the case the
> cluster is migrated for example (all the ips change). one could have
> the same hostname resolve to different ips depending on who's doing
> the lookup (this happens in AWS where the same elastic hostname
> resolves to private or public ip depending on where the peer is. so
> clients can talk from outside AWS via public ips and master etc. can
> talk over private ips).
>
> so lots of reasons i guess. doesn't the reverse ip lookup just once at
> RS startup time? (wondering how this reconciles with the  DNS being
> flaky after the cluster was up and running).
>
> On Thu, Jan 28, 2010 at 9:30 PM, Karthik Ranganathan
> <kranganathan@facebook.com> wrote:
>>
>> We did some more digging into this and here is the theory.
>>
>> 1. The regionservers use their local ip to lookup their hostnames and pass that to
the HMaster. The HMaster finds the server info by using this hostname as the key in the HashMap.
>>
>> HRegionServer.java
>> reinitialize() -
>> this.serverInfo = new HServerInfo(new HServerAddress(
>>      new InetSocketAddress(address.getBindAddress(),
>>      this.server.getListenerAddress().getPort())), System.currentTimeMillis(),
>>      this.conf.getInt("hbase.regionserver.info.port", 60030), machineName);
>>
>> In run() -
>> HMsg msgs[] = hbaseMaster.regionServerReport(
>>              serverInfo, outboundArray, getMostLoadedRegions());
>>
>>
>> 2. I have observed in the past that there could be some DNS flakiness which causes
the IP address of the machines to be returned as their hostnames. Guessing this is what happened.
>>
>>
>> 3. The HMaster looks in the map for the above IP address (masquerading as the server
name). It gets and does not find the entry in its map. So it assumes that this is a new region
server and issues a CALL_SERVER_STARTUP.
>>
>>
>> 4. The region server that receives it is in fact already running (under its real
hostname) and enters the "HMaster panic" mode and bad stuff happens.
>>
>> ServerManager.java in regionServerReport() -
>>    HServerInfo storedInfo = serversToServerInfo.get(info.getServerName());
>>    if (storedInfo == null) {
>>      // snip...
>>      return new HMsg[] {CALL_SERVER_STARTUP};
>>    }
>>
>>
>> Any reason why we use the hostname instead of the ip address in the map that stores
the regionserver info?
>>
>> Thanks
>> Karthik
>>
>>
>> -----Original Message-----
>> From: Karthik Ranganathan [mailto:kranganathan@facebook.com]
>> Sent: Thursday, January 28, 2010 3:58 PM
>> To: hbase-dev@hadoop.apache.org
>> Subject: Cannot locate root region
>>
>> Hey guys,
>>
>> Ran into some issues while testing and wanted to understand what has happened better.
Got the following exception when I went to the web UI
>>
>> Trying to contact region server 10.129.68.204:60020 for region .META.,,1, row '',
but failed after 3 attempts.
>> Exceptions:
>> org.apache.hadoop.hbase.NotServingRegionException: org.apache.hadoop.hbase.NotServingRegionException:
.META.,,1
>>        at org.apache.hadoop.hbase.regionserver.HRegionServer.getRegion(HRegionServer.java:2254)
>>        at org.apache.hadoop.hbase.regionserver.HRegionServer.openScanner(HRegionServer.java:1837)
>>        at sun.reflect.GeneratedMethodAccessor4.invoke(Unknown Source)
>>        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
>>        at java.lang.reflect.Method.invoke(Method.java:597)
>>        at org.apache.hadoop.hbase.ipc.HBaseRPC$Server.call(HBaseRPC.java:648)
>>        at org.apache.hadoop.hbase.ipc.HBaseServer$Handler.run(HBaseServer.java:915)
>>
>>
>> From a program that reads from a HBase table:
>> java.lang.reflect.UndeclaredThrowableException
>>        at $Proxy1.getRegionInfo(Unknown Source)
>>        at org.apache.hadoop.hbase.client.HConnectionManager$TableServers.locateRootRegion(HConnectionManager.java:985)
>>        at org.apache.hadoop.hbase.client.HConnectionManager$TableServers.locateRegion(HConnectionManager.java:625)
>>        at org.apache.hadoop.hbase.client.HConnectionManager$TableServers.locateRegion(HConnectionManager.java:601)
>>        at org.apache.hadoop.hbase.client.HConnectionManager$TableServers.locateRegionInMeta(HConnectionManager.java:675)
>> <snip>
>>
>>
>> Followed  up on the hmaster's log:
>>
>> 2010-01-28 11:21:16,148 INFO org.apache.hadoop.hbase.master.BaseScanner: RegionManager.metaScanner
scan of 1 row(s) of meta region {server: 10.129.68.204:60020, regionname: .META.,,1, startKey:
<>} complete
>> 2010-01-28 11:21:16,148 INFO org.apache.hadoop.hbase.master.BaseScanner: All 1 .META.
region(s) scanned
>> 2010-01-28 11:21:34,539 DEBUG org.apache.hadoop.hbase.master.ServerManager: Received
report from unknown server -- telling it to MSG_CALL_SERVER_STARTUP: 10.129.68.203,60020,1263605543210
>> 2010-01-28 11:21:35,622 INFO org.apache.hadoop.hbase.master.ServerManager: Received
start message from: hbasetest004.ash1.facebook.com,60020,1264706494600
>> 2010-01-28 11:21:36,649 DEBUG org.apache.hadoop.hbase.zookeeper.ZooKeeperWrapper:
Updated ZNode /hbase/rs/1264706494600 with data 10.129.68.203:60020
>> 2010-01-28 11:21:40,704 INFO org.apache.hadoop.ipc.HBaseServer: IPC Server handler
39 on 60000, call createTable({NAME => 'test1', FAMILIES => [{NAME => 'cf1', VERSIONS
=> '3', COMPRESSION => 'NONE', TTL => '2147483647', BLOCKSIZE => '65536', IN_MEMORY
=> 'false', BLOCKCACHE => 'true'}]}) from 10.131.29.183:63308: error: org.apache.hadoop.hbase.TableExistsException:
test1
>> org.apache.hadoop.hbase.TableExistsException: test1
>>        at org.apache.hadoop.hbase.master.HMaster.createTable(HMaster.java:792)
>>        at org.apache.hadoop.hbase.master.HMaster.createTable(HMaster.java:756)
>>        at sun.reflect.GeneratedMethodAccessor6.invoke(Unknown Source)
>>        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
>>        at java.lang.reflect.Method.invoke(Method.java:597)
>>        at org.apache.hadoop.hbase.ipc.HBaseRPC$Server.call(HBaseRPC.java:648)
>>        at org.apache.hadoop.hbase.ipc.HBaseServer$Handler.run(HBaseServer.java:915)
>>
>> From a hregionserver's logs:
>>
>> 2010-01-28 11:20:22,589 DEBUG org.apache.hadoop.hbase.io.hfile.LruBlockCache: Cache
Stats: Sizes: Total=19.661453MB (20616528), Free=2377.0137MB (2492479408), Max=2396.675MB
(2513095936), Counts: Blocks=0, Access=0, Hit=0, Miss=0, Evictions=0, Evicted=0, Ratios: Hit
Ratio=NaN%, Miss Ratio=NaN%, Evicted/Run=NaN
>> 2010-01-28 11:21:22,588 DEBUG org.apache.hadoop.hbase.io.hfile.LruBlockCache: Cache
Stats: Sizes: Total=19.661453MB (20616528), Free=2377.0137MB (2492479408), Max=2396.675MB
(2513095936), Counts: Blocks=0, Access=0, Hit=0, Miss=0, Evictions=0, Evicted=0, Ratios: Hit
Ratio=NaN%, Miss Ratio=NaN%, Evicted/Run=NaN
>> 2010-01-28 11:22:18,794 INFO org.apache.hadoop.hbase.regionserver.HRegionServer:
MSG_CALL_SERVER_STARTUP
>>
>>
>> The code says the following:
>>              case MSG_CALL_SERVER_STARTUP:
>>                // We the MSG_CALL_SERVER_STARTUP on startup but we can also
>>                // get it when the master is panicking because for instance
>>                // the HDFS has been yanked out from under it.  Be wary of
>>                // this message.
>>
>> Any ideas on what is going on? The best I can come up with is perhaps a flaky DNS
- would that explain this? This happened on three of our test clusters at almost the same
time. Also, what is the most graceful/simplest way to recover from this?
>>
>>
>> Thanks
>> Karthik
>>
>>
>

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