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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-11323) BucketCache all the time!
Date Sat, 14 Jun 2014 16:30:03 GMT

    [ https://issues.apache.org/jira/browse/HBASE-11323?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14031612#comment-14031612
] 

Andrew Purtell commented on HBASE-11323:
----------------------------------------

bq. But on creation, it only has Path context... nought else.

Yeah when opening a reader we only have the metadata in the HFile, we are disconnected from
schema at the HFile level. If you look at the patch for HBASE-9857, there are some TODOs where
we have regex constants down in HFile for what should be Store level detail (path and dir
layout conventions). We should hook up read side to Store. Possibly we could do that by adding
a method HFileContext Store#getFileContext(Path) ? Would set up a context with schema and
flags based on the Store level knowledge of what the Path encodes.

> 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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