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From Matthew LeMieux <...@mlogiciels.com>
Subject Re: NameNode crash - cannot start dfs - need help
Date Tue, 05 Oct 2010 18:25:57 GMT
Thank you Ayon, Allen and Todd for your suggestions. 

I was tempted to try to find the offending records in edits.new, but opted for simply moving
the file instead.  I kept the recently edited edits file in place. 

The namenode started up this time with no exceptions and appears to be running well; 	 hadoop
fsck / reports a healthy filesystem. 

Thank you, 

Matthew

On Oct 5, 2010, at 10:09 AM, Todd Lipcon wrote:

> On Tue, Oct 5, 2010 at 9:58 AM, Matthew LeMieux <mdl@mlogiciels.com> wrote:
> Thank you Todd. 
> 
> It does indeed seem like a challenge to find a record boundary, but if I wanted to do
it...   here is how I did it in case others are interested in doing the same.  
> 
> It looks like that value (0xFF) is referenced as OP_INVALID in the source file: [hadoop-dist]/src//hdfs/org/apache/hadoop/hdfs/server/namenode/FSEditLog.java.

> 
> Every record begins with an op code that describes the record.  The op codes are in the
range [0,14] (inclusive), except for OP_INVALID.  Each record type (based on op code) appears
to have a different format.  Additionally, it seems that the code for each record type has
several code paths to support different versions of the hdfs.  
> 
>  I looked in the error messages, and found the line number of the exception within the
switch statement in the code (in this case, line 563).  That told me that I was looking for
an op code of either 0x00 or 0x09.  I noticed that this particular code path had a record
type that looked like this: 
> [# bytes: name]
> 
> [1:op code][4:int length][2:file system path length][?:file system path text]
> 
> All I had to do was find a filesystem path, and look 7 bytes before it started.  If the
op code was a 0x00 or 0x09, then this was a candidate record. 
> 
> It would have been easier to just search for something from the error message (i.e. "12862"
for me) to find candidate records, but in my case that was in almost every record.  Additionally,
it would have also been easier to just search for instances of the op code, but in my case
one of the op codes (0x00) appears too often in the data to make that useful.   If your op
code is 0x03 for example, you will probably have a much easier time of it than I did.  
> 
> I was able to successfully and quickly find record boundaries and replace the op code
with 0xff.  After a few records I was back to the NPE exception that I was getting with a
zero length edits file: 
> 
> 2010-10-05 16:47:39,670 INFO org.apache.hadoop.hdfs.server.common.Storage: Edits file
/mnt/name/current/edits of size 157037 edits # 959 loaded in 0 seconds.
> 2010-10-05 16:47:39,671 ERROR org.apache.hadoop.hdfs.server.namenode.NameNode: java.lang.NullPointerException
>         at org.apache.hadoop.hdfs.server.namenode.FSDirectory.addChild(FSDirectory.java:1081)
>         at org.apache.hadoop.hdfs.server.namenode.FSDirectory.addChild(FSDirectory.java:1093)
>         at org.apache.hadoop.hdfs.server.namenode.FSDirectory.addNode(FSDirectory.java:996)
>         at org.apache.hadoop.hdfs.server.namenode.FSDirectory.unprotectedAddFile(FSDirectory.java:199)
>         at org.apache.hadoop.hdfs.server.namenode.FSEditLog.loadFSEdits(FSEditLog.java:627)
>         at org.apache.hadoop.hdfs.server.namenode.FSImage.loadFSEdits(FSImage.java:1022)
>         at org.apache.hadoop.hdfs.server.namenode.FSImage.loadFSImage(FSImage.java:830)
>         at org.apache.hadoop.hdfs.server.namenode.FSImage.recoverTransitionRead(FSImage.java:378)
>         at org.apache.hadoop.hdfs.server.namenode.FSDirectory.loadFSImage(FSDirectory.java:92)
> 
> One hurdle down, how do I get past the next one?
> 
> It's unclear whether you're getting the error in "edits" or "edits.new". From the above,
I'm guessing maybe "edits" is corrupt, so when you fixed the error there (by truncating a
few edits from the end), then the later edits in edits.new failed, because they depended on
a path that should have been created by "edits".
> 
> (BTW, what if I didn't want to keep my recent edits, and just wanted to start up the
namenode?   This is currently expensive downtime; I'd rather lose a small amount of data and
be up and running than continue the down time). 
> 
> If you really want to do this, you can remove "edits.new", and replace "edits" with a
file containing hex 0xffffffeeff I believe (edits header plus OP_INVALID)
> 
> -Todd
>  
> Oct 5, 2010, at 8:42 AM, Todd Lipcon wrote:
> 
>> Hi Matt,
>> 
>> If you want to keep your recent edits, you'll have to place an 0xFF at the beginning
of the most recent edit entry in the edit log. It's a bit tough to find these boundaries,
but you can try applying this patch and rebuilding:
>> 
>> https://issues.apache.org/jira/browse/hdfs-1378
>> 
>> This will tell you the offset of the broken entry ("recent opcodes") and you can
put an 0xff there to tie off the file before the corrupt entry.
>> 
>> -Todd
>> 
>> 
>> On Tue, Oct 5, 2010 at 8:16 AM, Matthew LeMieux <mdl@mlogiciels.com> wrote:
>> The namenode on an otherwise very stable HDFS cluster crashed recently.  The filesystem
filled up on the name node, which I assume is what caused the crash.    The problem has been
fixed, but I cannot get the namenode to restart.  I am using version CDH3b2  (hadoop-0.20.2+320).

>> 
>> The error is this: 
>> 
>> 2010-10-05 14:46:55,989 INFO org.apache.hadoop.hdfs.server.common.Storage: Edits
file /mnt/name/current/edits of size 157037 edits # 969 loaded in 0 seconds.
>> 2010-10-05 14:46:55,992 ERROR org.apache.hadoop.hdfs.server.namenode.NameNode: java.lang.NumberFormatException:
For input string: "12862^@^@^@^@^@^@^@^@"
>>         at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
>>         at java.lang.Long.parseLong(Long.java:419)
>>         at java.lang.Long.parseLong(Long.java:468)
>>         at org.apache.hadoop.hdfs.server.namenode.FSEditLog.readLong(FSEditLog.java:1355)
>>         at org.apache.hadoop.hdfs.server.namenode.FSEditLog.loadFSEdits(FSEditLog.java:563)
>>         at org.apache.hadoop.hdfs.server.namenode.FSImage.loadFSEdits(FSImage.java:1022)
>>         ...
>> 
>> This page (http://wiki.apache.org/hadoop/TroubleShooting) recommends editing the
edits file with a hex editor, but does not explain where the record boundaries are.  It is
a different exception, but seemed like a similar cause, the edits file.  I tried removing
a line at a time, but the error continues, only with a smaller size and edits #: 
>> 
>> 2010-10-05 14:37:16,635 INFO org.apache.hadoop.hdfs.server.common.Storage: Edits
file /mnt/name/current/edits of size 156663 edits # 966 loaded in 0 seconds.
>> 2010-10-05 14:37:16,638 ERROR org.apache.hadoop.hdfs.server.namenode.NameNode: java.lang.NumberFormatException:
For input string: "12862^@^@^@^@^@^@^@^@"
>>         at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
>>         at java.lang.Long.parseLong(Long.java:419)
>>         at java.lang.Long.parseLong(Long.java:468)
>>         at org.apache.hadoop.hdfs.server.namenode.FSEditLog.readLong(FSEditLog.java:1355)
>>         at org.apache.hadoop.hdfs.server.namenode.FSEditLog.loadFSEdits(FSEditLog.java:563)
>>         at org.apache.hadoop.hdfs.server.namenode.FSImage.loadFSEdits(FSImage.java:1022)
>>         ...
>> 
>> I tried removing the edits file altogether, but that failed with: java.io.IOException:
Edits file is not found
>> 
>> I tried with a zero length edits file, so it would at least have a file there, but
that results in an NPE: 
>> 
>> 2010-10-05 14:52:34,775 INFO org.apache.hadoop.hdfs.server.common.Storage: Edits
file /mnt/name/current/edits of size 0 edits # 0 loaded in 0 seconds.
>> 2010-10-05 14:52:34,776 ERROR org.apache.hadoop.hdfs.server.namenode.NameNode: java.lang.NullPointerException
>>         at org.apache.hadoop.hdfs.server.namenode.FSDirectory.addChild(FSDirectory.java:1081)
>>         at org.apache.hadoop.hdfs.server.namenode.FSDirectory.addChild(FSDirectory.java:1093)
>>         at org.apache.hadoop.hdfs.server.namenode.FSDirectory.addNode(FSDirectory.java:996)
>>         at org.apache.hadoop.hdfs.server.namenode.FSDirectory.unprotectedAddFile(FSDirectory.java:199)
>> 
>> 
>> Most if not all the files I noticed in the edits file are temporary files that will
be deleted once this thing gets back up and running anyway.    There is a closed ticket that
might be related: https://issues.apache.org/jira/browse/HDFS-686 ,  but the version I'm using
seems to already have HDFS-686 (according to http://archive.cloudera.com/cdh/3/hadoop-0.20.2+320/changes.html)
 
>> 
>> What do I have to do to get back up and running?
>> 
>> Thank you for your help, 
>> 
>> Matthew
>> 
>> 
>> 
>> 
>> 
>> -- 
>> Todd Lipcon
>> Software Engineer, Cloudera
> 
> 
> 
> 
> -- 
> Todd Lipcon
> Software Engineer, Cloudera


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