Hi Vinayak,
Sorry this is beyond my understanding. I would need to test furthet to
try and understand the problem.
Hope you'll find help from someone else
Ulul
Le 08/10/2014 07:18, Vinayak Borkar a écrit :
Hi Ulul,
I think I can explain why the sizes differ and the block names vary.
There is no client interaction. My client writes data and calls hsync,
and then writes more data to the same file. My understanding is that
under such circumstances, the file size is not reflected accurately in
HDFS until the file is actually closed. So the namenode's view of the
file size will be lower than the actual size of the data in the block.
If you look at the block closely, you will see that the block number
is the same for the two blocks. The part that is different is the
version number - this is consistent with HDFS's behavior when hsyncing
the output stream and then continuing to write more. It looks like the
name node is informed much later about the last block that the
datanode actually wrote.
My client was not started when the machine came back up. So all
changes seen in the FSCK output were owing to HDFS.
Vinayak
On 10/7/14, 2:37 PM, Ulul wrote:
Hi Vinayak
I find strange that the file should have a different size and the block
a different name.
Are you sure your writing client wasn't interfering ?
Ulul
Le 07/10/2014 19:41, Vinayak Borkar a écrit :
Trying again since I did not get a reply. Please let me know if I
should use a different forum to ask this question.
Thanks,
Vinayak
On 10/4/14, 8:45 PM, Vinayak Borkar wrote:
Hi,
I was experimenting with HDFS to push its boundaries on fault
tolerance.
Here is what I observed.
I am using HDFS from Hadoop 2.2. I started the NameNode and then a
single DataNode. I started writing to a DFS file from a Java client
periodically calling hsync(). After some time, I powered off the
machine
that was running this test (not shutdown, just abruptly powered off).
When the system came back up, and HDFS processes were up and HDFS was
out of safe mode, I ran fsck on the DFS filesystem (with -openforwrite
-files -blocks) options and here is the output:
/test/test.log 388970 bytes, 1 block(s), OPENFORWRITE: MISSING 1
blocks
of total size 388970 B
0.
BP-1471648347-10.211.55.100-1412458980748:blk_1073743243_2420{blockUCState=UNDER_CONSTRUCTION,
primaryNodeIndex=-1,
replicas=[ReplicaUnderConstruction[[DISK]DS-e5bed5ae-1fa9-45ed-8d4c-8006919b4d9c:NORMAL|RWR]]}
len=388970 MISSING!
Status: CORRUPT
Total size: 7214119 B
Total dirs: 54
Total files: 232
Total symlinks: 0
Total blocks (validated): 214 (avg. block size 33710 B)
********************************
CORRUPT FILES: 1
MISSING BLOCKS: 1
MISSING SIZE: 388970 B
********************************
Minimally replicated blocks: 213 (99.53271 %)
Over-replicated blocks: 0 (0.0 %)
Under-replicated blocks: 213 (99.53271 %)
Mis-replicated blocks: 0 (0.0 %)
Default replication factor: 3
Average block replication: 0.9953271
Corrupt blocks: 0
Missing replicas: 426 (66.35514 %)
Number of data-nodes: 1
Number of racks: 1
FSCK ended at Sat Oct 04 23:09:40 EDT 2014 in 47 milliseconds
I just let the system sit for some time and reran fsck (after about
15-20 mins) and surprisingly the output was very different. The
corruption was magically gone:
/test/test.log 1859584 bytes, 1 block(s): Under replicated
BP-1471648347-10.211.55.100-1412458980748:blk_1073743243_2421. Target
Replicas is 3 but found 1 replica(s).
0. BP-1471648347-10.211.55.100-1412458980748:blk_1073743243_2421
len=1859584 repl=1
Status: HEALTHY
Total size: 8684733 B
Total dirs: 54
Total files: 232
Total symlinks: 0
Total blocks (validated): 214 (avg. block size 40582 B)
Minimally replicated blocks: 214 (100.0 %)
Over-replicated blocks: 0 (0.0 %)
Under-replicated blocks: 214 (100.0 %)
Mis-replicated blocks: 0 (0.0 %)
Default replication factor: 3
Average block replication: 1.0
Corrupt blocks: 0
Missing replicas: 428 (66.666664 %)
Number of data-nodes: 1
Number of racks: 1
FSCK ended at Sat Oct 04 23:24:23 EDT 2014 in 63 milliseconds
The filesystem under path '/' is HEALTHY
So my question is this: What just happened? How did the NameNode
recover
that missing block and why did it take 15 mins or so? Is there some
kind
of a lease on the file (because of the open nature) that expired after
the 15-20 mins? Can someone with knowledge of HDFS internals please
shed
some light on what could possibly be going on or point me to
sections of
the code that could answer my questions? Also is there a way to speed
this process up? Like say trigger the expiration of the lease
(assuming
it is a lease).
Thanks,
Vinayak
