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https://issues.apache.org/jira/browse/HBASE-15064?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15082513#comment-15082513
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Anoop Sam John commented on HBASE-15064:
----------------------------------------
Thanks for the review Stack.
bq. Only odd thing is the location of the test. Is there not a better place for
it than its own class?
I think it is fine as a UT. The issue is clearly coming up. The issue was
that even if we are at the end of the MBB, the hasRemaining return true. It is
not an issue with MBB as such. It as an issue with
ByteBufferArray#asSubBuffer() which returns the 0 length BB as the last buffer
within MBB. That is why I thought a UT for ByteBufferArray#asSubBuffer() for
hasRemaining() is good enough.
It might be difficult to mock the same situation in an FT which is doing the
actual cells read from a Scanner. Because this will happen for the HFileBlock
read from the end of the bucket cache.
> Possbile Bug in MultiByteBuffer
> -------------------------------
>
> Key: HBASE-15064
> URL: https://issues.apache.org/jira/browse/HBASE-15064
> Project: HBase
> Issue Type: Bug
> Components: io
> Affects Versions: 2.0.0
> Reporter: deepankar
> Assignee: Anoop Sam John
> Priority: Critical
> Fix For: 2.0.0
>
> Attachments: HBASE-15064.patch
>
>
> While running the newer patches on our production system, I saw this error
> come couple of times
> {noformat}
> ipc.RpcServer: Unexpected throwable object
> 2016-01-01 16:42:56,090 ERROR
> [B.defaultRpcServer.handler=20,queue=20,port=60020] ipc.RpcServer: Unexpected
> throwable object
> java.nio.BufferUnderflowException
> at java.nio.Buffer.nextGetIndex(Buffer.java:500)
> at java.nio.DirectByteBuffer.get(DirectByteBuffer.java:249)
> at org.apache.hadoop.hbase.nio.MultiByteBuff.get(MultiByteBuff.java:494)
> at
> org.apache.hadoop.hbase.io.encoding.FastDiffDeltaEncoder$1.decode(FastDiffDeltaEncoder.java:402)
>
> at
> org.apache.hadoop.hbase.io.encoding.FastDiffDeltaEncoder$1.decodeNext(FastDiffDeltaEncoder.java:517)
>
> at
> org.apache.hadoop.hbase.io.encoding.BufferedDataBlockEncoder$BufferedEncodedSeeker.next(BufferedDataBlockEncoder.java:815)
> at
> org.apache.hadoop.hbase.regionserver.StoreFileScanner.next(StoreFileScanner.java:138)
> {noformat}
> Looking at the get code
> {code}
> if (this.curItem.remaining() == 0) {
> if (items.length - 1 == this.curItemIndex) {
> // means cur item is the last one and we wont be able to read a long.
> Throw exception
> throw new BufferUnderflowException();
> }
> this.curItemIndex++;
> this.curItem = this.items[this.curItemIndex];
> }
> return this.curItem.get();
> {code}
> Can the new currentItem have zero elements (position == limit), does it make
> sense to change the {{if}} to {{while}} ? {{while (this.curItem.remaining()
> == 0)}}. This logic is repeated may make sense abstract to a new function if
> we plan to change to {{if}} to {{while}}
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