Namenode unable to start due to truncated fstime
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Key: HDFS-1220
URL: https://issues.apache.org/jira/browse/HDFS-1220
Project: Hadoop HDFS
Issue Type: Bug
Components: name-node
Affects Versions: 0.20.1
Reporter: Thanh Do
- Summary: updating fstime file on disk is not atomic, so it is possible that
if a crash happens in the middle, next time when NameNode reboots, it will
read stale fstime, hence unable to start successfully.
- Details:
Below is the code for updating fstime file on disk
void writeCheckpointTime(StorageDirectory sd) throws IOException {
if (checkpointTime < 0L)
return; // do not write negative time
File timeFile = getImageFile(sd, NameNodeFile.TIME);
if (timeFile.exists()) { timeFile.delete(); }
DataOutputStream out = new DataOutputStream(
new FileOutputStream(timeFile));
try {
out.writeLong(checkpointTime);
} finally {
out.close();
}
}
Basically, this involve 3 steps:
1) delete fstime file (timeFile.delete())
2) truncate fstime file (new FileOutputStream(timeFile))
3) write new time to fstime file (out.writeLong(checkpointTime))
If a crash happens after step 2 and before step 3, in the next reboot, NameNode
got an exception when reading the time (8 byte) from an empty fstime file.
This bug was found by our Failure Testing Service framework:
http://www.eecs.berkeley.edu/Pubs/TechRpts/2010/EECS-2010-98.html
For questions, please email us: Thanh Do (than...@cs.wisc.edu) and
Haryadi Gunawi (hary...@eecs.berkeley.edu
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