Race condition between rollEditLog or rollFSImage ant FSEditsLog.write
operations corrupts edits log
-----------------------------------------------------------------------------------------------------
Key: HDFS-909
URL: https://issues.apache.org/jira/browse/HDFS-909
Project: Hadoop HDFS
Issue Type: Bug
Components: name-node
Affects Versions: 0.21.0, 0.22.0
Environment: CentOS
Reporter: Cosmin Lehene
Priority: Blocker
Fix For: 0.21.0, 0.22.0
closing the edits log file can race with write to edits log file operation
resulting in OP_INVALID end-of-file marker being initially overwritten by the
concurrent (in setReadyToFlush) threads and then removed twice from the buffer,
losing a good byte from edits log.
Example:
{code}
FSNameSystem.rollEditLog() -> FSEditLog.divertFileStreams() ->
FSEditLog.closeStream() -> EditLogOutputStream.setReadyToFlush()
FSNameSystem.rollEditLog() -> FSEditLog.divertFileStreams() ->
FSEditLog.closeStream() -> EditLogOutputStream.flush() ->
EditLogFileOutputStream.flushAndSync()
OR
FSNameSystem.rollFSImage() -> FSIMage.rollFSImage() -> FSEditLog.purgeEditLog()
-> FSEditLog.revertFileStreams() -> FSEditLog.closeStream()
->EditLogOutputStream.setReadyToFlush()
FSNameSystem.rollFSImage() -> FSIMage.rollFSImage() -> FSEditLog.purgeEditLog()
-> FSEditLog.revertFileStreams() -> FSEditLog.closeStream()
->EditLogOutputStream.flush() -> EditLogFileOutputStream.flushAndSync()
VERSUS
FSNameSystem.completeFile -> FSEditLog.logSync() ->
EditLogOutputStream.setReadyToFlush()
FSNameSystem.completeFile -> FSEditLog.logSync() -> EditLogOutputStream.flush()
-> EditLogFileOutputStream.flushAndSync()
OR
Any FSEditLog.write
{code}
Access on the edits flush operations is synchronized only in the
FSEdits.logSync() method level. However at a lower level access to
EditsLogOutputStream setReadyToFlush(), flush() or flushAndSync() is NOT
synchronized. These can be called from concurrent threads like in the example
above
So if a rollEditLog or rollFSIMage is happening at the same time with a write
operation it can race for EditLogFileOutputStream.setReadyToFlush that will
overwrite the the last byte (normally the FSEditsLog.OP_INVALID which is the
"end-of-file marker") and then remove it twice (from each thread) in
flushAndSync()! Hence there will be a valid byte missing from the edits log
that leads to a SecondaryNameNode silent failure and a full HDFS failure upon
cluster restart.
We got to this point after investigating a corrupted edits file that made HDFS
unable to start with
{code:title=namenode.log}
java.io.IOException: Incorrect data format. logVersion is -20 but
writables.length is 768.
at
org.apache.hadoop.hdfs.server.namenode.FSEditLog.loadEditRecords(FSEditLog.java:450
{code}
In the edits file we found the first 2 entries:
{code:title=edits}
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
...
{code}
This is the completeFile operation that's missing the last byte
{code:title=completeFile}
FFFFFFEC0900000005003F2F68626173652F64656D6F5F5F75736572732F636F6D70616374696F6E2E6469722F3336343035313634362F38333238313438373139303730333137323739000133000D31323631303832363331383335000D313236313038323632383039340008363731303838363400000003F6CBB87EF376E3E600000000040000000000000000039665F9549DE069A5735E00000000040000000000000000039665ADCC71A050B16ABF00000000015A179A0000000000039665066861646F6F700A737570657267726F757001??
{code}
followed by a rename operation
{code:Title=rename}
0100000003003F2F68626173652F64656D6F5F5F75736572732F636F6D70616374696F6E2E6469722F3336343035313634362F3833323831343837313930373033313732373900352F68626173652F64656D6F5F5F75736572732F3336343035313634362F746573742F36393137333831323838333034343734333836000D31323631303832363331383639
{code}
The first byte of the rename was instead read as part of the completeFile()
operation. This resulted in reading the next operation as 0x00 (OP_ADD)
followed by an int (length) which would have been 0x0000030 which is 768 that
was read and failed in the following code
{code:Title=FSEditLog.java}
case OP_ADD:
case OP_CLOSE: {
// versions > 0 support per file replication
// get name and replication
int length = in.readInt();
if (-7 == logVersion && length != 3||
-17 < logVersion && logVersion < -7 && length != 4 ||
logVersion <= -17 && length != 5) {
throw new IOException("Incorrect data format." +
" logVersion is " + logVersion +
" but writables.length is " +
length + ". ");
{code}
Filling the missing byte with a value resulted in correct interpretation of the
0x01 (OP_RENAME) and correct parsing for the rest of the edits file (>1MB)
This theory is also supported by the NameNode log file from the date the
corruption took place:
{code:title=namenode.log}
2009-12-17 12:43:51,276 INFO
org.apache.hadoop.hdfs.server.namenode.FSNamesystem: Roll Edit Log from
10.72.17.162
2009-12-17 12:43:51,338 INFO org.apache.hadoop.hdfs.StateChange: BLOCK*
NameSystem.addStoredBlock: blockMap updated: 10.72.17.165:50010 is added to
blk_-480585673051114658_235109{blockUCState=UNDER_CONSTRUCTION,
primaryNodeIndex=-1,
replicas=[ReplicaUnderConstruction[10.72.17.166:50010|RBW],
ReplicaUnderConstruction[10.72.17.165:50010|RBW],
ReplicaUnderConstruction[10.72.17.167:50010|RBW]]} size 67108864
2009-12-17 12:43:51,339 INFO org.apache.hadoop.hdfs.StateChange: BLOCK*
NameSystem.addStoredBlock: blockMap updated: 10.72.17.166:50010 is added to
blk_-480585673051114658_235109{blockUCState=UNDER_CONSTRUCTION,
primaryNodeIndex=-1,
replicas=[ReplicaUnderConstruction[10.72.17.166:50010|RBW],
ReplicaUnderConstruction[10.72.17.165:50010|RBW],
ReplicaUnderConstruction[10.72.17.167:50010|RBW]]} size 67108864
2009-12-17 12:43:51,342 INFO org.apache.hadoop.hdfs.StateChange: BLOCK*
NameSystem.allocateBlock:
/hbase/demo__users/compaction.dir/364051646/8328148719070317279.
blk_-5923234476536534337_235109{blockUCState=UNDER_CONSTRUCTION,
primaryNodeIndex=-1,
replicas=[ReplicaUnderConstruction[10.72.17.166:50010|RBW],
ReplicaUnderConstruction[10.72.17.164:50010|RBW],
ReplicaUnderConstruction[10.72.17.163:50010|RBW]]}
2009-12-17 12:43:51,352 INFO org.apache.hadoop.hdfs.StateChange: BLOCK*
NameSystem.addStoredBlock: blockMap updated: 10.72.17.167:50010 is added to
blk_-480585673051114658_235109{blockUCState=COMMITTED, primaryNodeIndex=-1,
replicas=[ReplicaUnderConstruction[10.72.17.166:50010|RBW],
ReplicaUnderConstruction[10.72.17.165:50010|RBW],
ReplicaUnderConstruction[10.72.17.167:50010|RBW]]} size 67108864
2009-12-17 12:43:51,833 INFO org.apache.hadoop.hdfs.StateChange: BLOCK*
NameSystem.addStoredBlock: blockMap updated: 10.72.17.163:50010 is added to
blk_-5923234476536534337_235109{blockUCState=UNDER_CONSTRUCTION,
primaryNodeIndex=-1,
replicas=[ReplicaUnderConstruction[10.72.17.166:50010|RBW],
ReplicaUnderConstruction[10.72.17.164:50010|RBW],
ReplicaUnderConstruction[10.72.17.163:50010|RBW]]} size 22681498
2009-12-17 12:43:51,834 INFO org.apache.hadoop.hdfs.StateChange: BLOCK*
NameSystem.addStoredBlock: blockMap updated: 10.72.17.164:50010 is added to
blk_-5923234476536534337_235109{blockUCState=UNDER_CONSTRUCTION,
primaryNodeIndex=-1,
replicas=[ReplicaUnderConstruction[10.72.17.166:50010|RBW],
ReplicaUnderConstruction[10.72.17.164:50010|RBW],
ReplicaUnderConstruction[10.72.17.163:50010|RBW]]} size 22681498
2009-12-17 12:43:51,834 INFO org.apache.hadoop.hdfs.StateChange: BLOCK*
NameSystem.addStoredBlock: blockMap updated: 10.72.17.166:50010 is added to
blk_-5923234476536534337_235109{blockUCState=UNDER_CONSTRUCTION,
primaryNodeIndex=-1,
replicas=[ReplicaUnderConstruction[10.72.17.166:50010|RBW],
ReplicaUnderConstruction[10.72.17.164:50010|RBW],
ReplicaUnderConstruction[10.72.17.163:50010|RBW]]} size 22681498
2009-12-17 12:43:51,835 INFO org.apache.hadoop.hdfs.StateChange: DIR*
NameSystem.completeFile: file
/hbase/demo__users/compaction.dir/364051646/8328148719070317279 is closed by
DFSClient_-1989779667
2009-12-17 12:43:51,835 INFO
org.apache.hadoop.hdfs.server.namenode.FSNamesystem: Roll FSImage from
10.72.17.162
2009-12-17 12:43:51,870 INFO
org.apache.hadoop.hdfs.server.namenode.FSNamesystem.audit: ugi=hadoop,hadoop
ip=/10.72.17.166 cmd=rename
src=/hbase/demo__users/compaction.dir/364051646/8328148719070317279
dst=/hbase/demo__users/364051646/test/6917381288304474386
perm=hadoop:supergroup:rw-r--r--
{code}
The last 3 entries show a completeFile operation followed by a rollFSIMage
operation followed by a rename operation. This is where most probably the race
condition took place.
Synchronizing access to EditLogOutputStream could fix the problem, however
other race or deadlocks may still occur.
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