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https://issues.apache.org/jira/browse/HBASE-4027?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13054639#comment-13054639
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Jonathan Gray commented on HBASE-4027:
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In the new HFile v2 over in HBASE-3857 the block cache interface changes from
ByteBuffer to HeapSize. So you can now put anything you want into the cache
that implements HeapSize (there is a new HFileBlock that is used in HFile v2).
One big question is whether you're going to make copies out of the direct byte
buffers on each read of that block, or if you're going to change KeyValue to
use the ByteBuffer interface (or some other) instead of the byte[] directly.
With a DBB you can't get access to an underlying byte[].
> Enable direct byte buffers LruBlockCache
> ----------------------------------------
>
> Key: HBASE-4027
> URL: https://issues.apache.org/jira/browse/HBASE-4027
> Project: HBase
> Issue Type: Improvement
> Reporter: Jason Rutherglen
> Priority: Minor
>
> Java offers the creation of direct byte buffers which are allocated outside
> of the heap.
> They need to be manually free'd, which can be accomplished using an
> documented {{clean}} method.
> The feature will be optional. After implementing, we can benchmark for
> differences in speed and garbage collection observances.
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