HBase Exception: org.apache.hadoop.hbase.UnknownRowLockException - hadoop

Question

I'm running a sample code I wrote to test HBase lockRow() and unlockRow() methods. The sample code is below:
HTable table = new HTable(config, "test");
RowLock rowLock = table.lockRow(Bytes.toBytes(row));
System.out.println("Obtained rowlock on " + row + "\nRowLock: " + rowLock);
Put p = new Put(Bytes.toBytes(row));
p.add(Bytes.toBytes("colFamily"), Bytes.toBytes(colFamily), Bytes.toBytes(value));
table.put(p);
System.out.println("put row");
table.unlockRow(rowLock);
System.out.println("Unlocked row!");
When I execute my code, I get an UnknownRowLockException. The documentation says that this error is thrown when an unknown row lock is passed to the region servers. I'm not sure how this is happening & how to resolve it.
The stack trace is below:
Obtained rowlock on row2
RowLock: org.apache.hadoop.hbase.client.RowLock#15af33d6
put row
Exception in thread "main" org.apache.hadoop.hbase.UnknownRowLockException: org.apache.hadoop.hbase.UnknownRowLockException: 5763272717012243790
at org.apache.hadoop.hbase.regionserver.HRegionServer.unlockRow(HRegionServer.java:2099)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.hadoop.hbase.ipc.HBaseRPC$Server.call(HBaseRPC.java:604)
at org.apache.hadoop.hbase.ipc.HBaseServer$Handler.run(HBaseServer.java:1055)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at org.apache.hadoop.hbase.RemoteExceptionHandler.decodeRemoteException(RemoteExceptionHandler.java:96)
at org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation.translateException(HConnectionManager.java:1268)
at org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation.getRegionServerWithRetries(HConnectionManager.java:1014)
at org.apache.hadoop.hbase.client.HTable.unlockRow(HTable.java:870)
at HelloWorld.Hello.HelloWorld.main(HelloWorld.java:41)
EDIT:
I just realized that I should be printing rowLock.getLockId() instead of rowLock. I did this and compared it to the rowlock in the stack trace, and they are the same, so I'm not sure why the UnknownRowLockException occurs.

Answer 1

Please change the 'file descriptor limit' on the underlying system.
On linux you can do this with ulimit
Note that HBase prints in its logs as the first line the ulimit its seeing.

Answer 2

I was able to resolve this error in this way:
The rowLock being obtained needs to be passed as a parameter to the put constructor.
HTable table = new HTable(config, "test");
RowLock rowLock = table.lockRow(Bytes.toBytes(row));
System.out.println("Obtained rowlock on " + row + "\nRowLock: " + rowLock);
Put p = new Put(Bytes.toBytes(row), rowLock);
p.add(Bytes.toBytes("colFamily"), Bytes.toBytes(colFamily), Bytes.toBytes(value));
table.put(p);
System.out.println("put row");
table.unlockRow(rowLock);
System.out.println("Unlocked row!");
In my earlier approach, a rowLock was being obtained on a row of the table. However, since the rowLock was not used (not passed to put constructor), when I call the unlockRow method, the method waits for 60 seconds (lock timeout) to check if the lock has been used. After 60 seconds, the lock expires, and I end up with UnknownRowLockException