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https://issues.apache.org/jira/browse/HBASE-11425?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14356459#comment-14356459
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Anoop Sam John commented on HBASE-11425:
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You say about this case hbase.block.data.cachecompressed = true right? Yes
this recently added feature allow to keep block data in compressed form in BC.
When this block is read from BC, these happens
Step 1 : We create a new on heap buffer and copy compressed data from buckets
into it. Make an HFileBlock backed by this compressed data
Step 2 : Unpack this block. Then we will create a new byte[] with size equal
to the uncompresed data size for this block. The Compress algo will do
uncompress of the block data into this new buffer
As in our changes we avoid this step 1 new buffer and copy need. We create a
block backed by MBB. We have new InputStream over MBB and pass that for
uncomress. Yes Step 2 will be still there.
So adv here also. Make some sense?
> Cell/DBB end-to-end on the read-path
> ------------------------------------
>
> Key: HBASE-11425
> URL: https://issues.apache.org/jira/browse/HBASE-11425
> Project: HBase
> Issue Type: Umbrella
> Components: regionserver, Scanners
> Affects Versions: 0.99.0
> Reporter: Anoop Sam John
> Assignee: Anoop Sam John
> Attachments: Offheap reads in HBase using BBs_final.pdf
>
>
> Umbrella jira to make sure we can have blocks cached in offheap backed cache.
> In the entire read path, we can refer to this offheap buffer and avoid onheap
> copying.
> The high level items I can identify as of now are
> 1. Avoid the array() call on BB in read path.. (This is there in many
> classes. We can handle class by class)
> 2. Support Buffer based getter APIs in cell. In read path we will create a
> new Cell with backed by BB. Will need in CellComparator, Filter (like SCVF),
> CPs etc.
> 3. Avoid KeyValue.ensureKeyValue() calls in read path - This make byte copy.
> 4. Remove all CP hooks (which are already deprecated) which deal with KVs.
> (In read path)
> Will add subtasks under this.
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