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https://issues.apache.org/jira/browse/HBASE-15063?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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deepankar updated HBASE-15063:
------------------------------
Assignee: deepankar
Status: Patch Available (was: Open)
> Bug(s) in MultiByteBuf
> ----------------------
>
> Key: HBASE-15063
> URL: https://issues.apache.org/jira/browse/HBASE-15063
> Project: HBase
> Issue Type: Bug
> Components: io, Performance
> Affects Versions: 2.0.0
> Reporter: deepankar
> Assignee: deepankar
> Priority: Blocker
> Attachments: HBASE-15063.patch
>
>
> In MutliByteBuff there are couple of inconsistencies, one is in the toBytes
> function where the offset for copying in the initial element is not being
> reset with respect to the element
> {code}
> public byte[] toBytes(int offset, int length) {
> byte[] output = new byte[length];
> int itemIndex = getItemIndex(offset);
> ByteBuffer item = this.items[itemIndex];
> // the offset has to be reset here to the items offset
> // should be offset = offset - itemBeingPos[itemIndex]
> int toRead = item.limit() - offset;
> int destinationOffset = 0;
> . . . .
> {code}
> Since there is already an existing function get to copy to an byte array it
> is better we reuse the function here, I attached a patch with a corresponding
> unit test. (HBASE-XXXX.patch)
> Another inconsistency I noticed is that there is lack of some consistency in
> using the position marker of the bytebuffers passed, In the constructor we
> noting the beginning offsets of each bytebuffer in the {{itemBeginPos}} array
> we are using these position markers in most of the absolute index functions
> such as {{get(index)}}, {{put(index, byte)}}, {{toBytes}},
> {{get(int,byte[],int,int)}} to find the current item to access. There are two
> problems with this
> # The array {{itemBeginPos}} is not being updated whenever there are some
> writes to internal bytebuffers (remember {{itemBeginPos}} depends on the
> {{bytebuffer.position()}} of the internal bytebuffers and the position marker
> is changed whenever some writes happen to bytebuffers)
> # Also the position marker is not being used in any of the index functions
> for example here in the get function
> {code}
> @Override
> public byte get(int index) {
> int itemIndex = getItemIndex(index);
> return ByteBufferUtils.toByte(this.items[itemIndex], index -
> this.itemBeginPos[itemIndex]);
> }
> {code}
> where the the index I think should be {{index -
> this.itemBeginPos\[itemIndex\] + items\[itemIndex\].position()}} because we
> are using the position marker to calculate the offsets.
> There are two solutions I think for this
> # The simple solution I feel for this should be probably ignoring the
> position marker while calculating the {{itemBeginPos}} array which will unify
> the semantics
> # Not use this array at all and iterate over bytebuffers every time for the
> {{getItemIndex}} function and also use the position marker before calling the
> {{ByteBufferUtils}} functions
> I can put up a patch for the second part if we decide which way to go.
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