[HBASE-22127] Ensure that the block cached in the LRUBlockCache offheap is allocated from heap - ASF JIRA

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Type: Sub-task
Status: Closed
Priority: Major
Resolution: Fixed
Affects Version/s: None
Fix Version/s: 3.0.0-alpha-1, 2.3.0
Component/s: None
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Description

In here [1], anoop.hbase pointed out an crtial problem , I pasted here:

So if we read from HDFS into a pooled BB and then give to LRU cache for caching (ya mostly cache on read might be true) we will cache the block which is backed by this pooled DBB? Unless the block is evicted , this BB wont go back to pool. I think this is some thing we can not livw with !! For LRU cache the sizing itself is based on what % of heap size we can grow. But here in effect we are occupying the off heap space for the cached blocks. All the sizing assumptions and calc going out of control !

It's indeed an big problem here. so we can only make the block ref to an heap area if we use LRUCache (both LruBlockCache and CombinedBlockCache case). Or we can also make the lru cache offheap ?

I think we can introduce an switch indicate that whether the lru block cache offheap or not, if heap, then coping those bytes from ByteBuff to heap.

https://reviews.apache.org/r/70153/diff/6?file=2133545#file2133545line398