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From "Anoop Sam John (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-11323) BucketCache all the time!
Date Sat, 14 Jun 2014 15:58:01 GMT

    [ https://issues.apache.org/jira/browse/HBASE-11323?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14031609#comment-14031609
] 

Anoop Sam John commented on HBASE-11323:
----------------------------------------

{quote}
bq.block buf refer the offheap memory? So in the read path, the Cells will refer to this memory?

Yes, that's what I'm suggesting.
{quote}
So we have to make sure the read path having Cell flowing through. (I think this is mostly
done) 
And the Cell should be supported being backed by BB. (offheap) We will need new comparators.

The Cell interface is having get***Array() APIs which return byte[]. We use them for the compare.
 When the Cells are backed by BB, calling these APIs will need us to create temp byte[] objects
and copying.  Need ways to solve this.


> BucketCache all the time!
> -------------------------
>
>                 Key: HBASE-11323
>                 URL: https://issues.apache.org/jira/browse/HBASE-11323
>             Project: HBase
>          Issue Type: Sub-task
>          Components: io
>            Reporter: stack
>             Fix For: 0.99.0
>
>         Attachments: ReportBlockCache.pdf
>
>
> One way to realize the parent issue is to just enable bucket cache all the time; i.e.
always have offheap enabled.  Would have to do some work to make it drop-dead simple on initial
setup (I think it doable).
> So, upside would be the offheap upsides (less GC, less likely to go away and never come
back because of full GC when heap is large, etc.).
> Downside is higher latency.   In Nick's BlockCache 101 there is little to no difference
between onheap and offheap.  In a basic compare doing scans and gets -- details to follow
-- I have BucketCache deploy about 20% less ops than LRUBC when all incache and maybe 10%
less ops when falling out of cache.   I can't tell difference in means and 95th and 99th are
roughly same (more stable with BucketCache).  GC profile is much better with BucketCache --
way less.  BucketCache uses about 7% more user CPU.
> More detail on comparison to follow.
> I think the numbers disagree enough we should probably do the [~lhofhansl] suggestion,
that we allow you to have a table sit in LRUBC, something the current bucket cache layout
does not do.



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