[HADOOP-2073] Datanode corruption if machine dies while writing VERSION file

• Type: Bug
• Status: Closed
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: 0.14.0
• Fix Version/s: 0.15.0
• Assignee: Konstantin Shvachko
• Reporter: Michael Bieniosek
• Created: 18/Oct/07 00:32
• Updated: 08/Jul/09 16:42
• Resolved: 24/Oct/07 18:41

Description

Yesterday, due to a bad mapreduce job, some of my machines went on OOM killing sprees and killed a bunch of datanodes, among other processes. Since my monitoring software kept trying to bring up the datanodes, only to have the kernel kill them off again, each machine's datanode was probably killed many times. A large percentage of these datanodes will not come up now, and write this message to the logs:

2007-10-18 00:23:28,076 ERROR org.apache.hadoop.dfs.DataNode: org.apache.hadoop.dfs.InconsistentFSStateException: Directory /hadoop/dfs/data is in an inconsistent state: file VERSION is invalid.

When I check, /hadoop/dfs/data/current/VERSION is an empty file. Consequently, I have to delete all the blocks on the datanode and start over. Since the OOM killing sprees happened simultaneously on several datanodes in my DFS cluster, this could have crippled my dfs cluster.

I checked the hadoop code, and in org.apache.hadoop.dfs.Storage, I see this:
{{{
/**

• Write version file.
• @throws IOException
  */
  void write() throws IOException { corruptPreUpgradeStorage(root); write(getVersionFile()); }

void write(File to) throws IOException {
Properties props = new Properties();
setFields(props, this);
RandomAccessFile file = new RandomAccessFile(to, "rws");
FileOutputStream out = null;
try

{ file.setLength(0); file.seek(0); out = new FileOutputStream(file.getFD()); props.store(out, null); }

finally {
if (out != null)

{ out.close(); }

file.close();
}
}
}}}

So if the datanode dies after file.setLength(0), but before props.store(out, null), the VERSION file will get trashed in the corrupted state I see. Maybe it would be better if this method created a temporary file VERSION.tmp, and then copied it to VERSION, then deleted VERSION.tmp? That way, if VERSION was detected to be corrupt, the datanode could look at VERSION.tmp to recover the data.