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https://issues.apache.org/jira/browse/HBASE-12295?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14566285#comment-14566285
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stack commented on HBASE-12295:
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[~anoop.hbase]
bq. Here once we get the cells, we will see whether it is marked using the new
Interface, if so we will do copy to a new Cell. And then this new cell is going
to be passed to CPs as well as HRS and above layers. Am I making it clear now?
Yes
CPs will have means of avoiding copy. Thats good.
bq. Because if we do so, every time next() comes, we have to ask the cache to
give me the cached block. This is not happening now. So we would like to avoid
this overhead.
You mean, the scanners are parked at a particular location so when scan comes
back in, we just continue? If it makes life easier, maybe we undo this and have
each 'next' invocation be a new scan (An old @nicolas liochon issue suggesting
we copy an amz db was suggesting this... but some pushback). I understand
though now that you want to preserve the old behavior. Makes sense. But if it
makes it all more complicated, then we might want to reexamine (scan would be
more like a get then?)
bq. But there can be N results which have the ref to same block(s) no? So it is
bit complicated then.
Don't these each have their own ref count?
bq. Also we did not want the concept of blocks or cache to come to upper layers
after the HFileScanner layer.
+1 on this (if my Result suggestion makes us go against this principal, then it
is not a good suggestion)
> Prevent block eviction under us if reads are in progress from the BBs
> ---------------------------------------------------------------------
>
> Key: HBASE-12295
> URL: https://issues.apache.org/jira/browse/HBASE-12295
> Project: HBase
> Issue Type: Sub-task
> Components: regionserver, Scanners
> Reporter: ramkrishna.s.vasudevan
> Assignee: ramkrishna.s.vasudevan
> Fix For: 2.0.0
>
> Attachments: HBASE-12295.pdf, HBASE-12295_trunk.patch
>
>
> While we try to serve the reads from the BBs directly from the block cache,
> we need to ensure that the blocks does not get evicted under us while
> reading. This JIRA is to discuss and implement a strategy for the same.
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