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From "Anoop Sam John (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-15314) Allow more than one backing file in bucketcache
Date Wed, 09 Mar 2016 16:35:40 GMT

    [ https://issues.apache.org/jira/browse/HBASE-15314?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15187363#comment-15187363
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Anoop Sam John commented on HBASE-15314:
----------------------------------------

Amal said it.
The decision of where to write (I mean which offset) is being taken NOT within IOEngine impl
but at BucketAllocator level.
It is NOT always true that we will 1st write and fill 1st file and then go to 2nd.  There
is a bucket allocation happening 1st.  The buckets will be having some fixed size. By default
we have 4+1 KB, 8+1 KB... 512+1 KB sized buckets.  (This is configurable)..  So we will make
buckets and fix offset to each of these buckets.    When a new block comes to be cached, we
will 1st see which bucket it can go. We will pick up a size which is least size with size
>= block size.   And we will see within that where to write. This offset is being passed.
So in order to make sure we have equi distribution while writing blocks, we will need change
in top layer of bucket allocator.
Ya once the cache is almost filled, the read will be distributed. Write happens in an async
way. So perf gain because of parallel writes to diff disks might not be that relevant.   Ya
still it will be best we can distribute load from begin and write load also..  

> Allow more than one backing file in bucketcache
> -----------------------------------------------
>
>                 Key: HBASE-15314
>                 URL: https://issues.apache.org/jira/browse/HBASE-15314
>             Project: HBase
>          Issue Type: Sub-task
>          Components: BucketCache
>            Reporter: stack
>            Assignee: Amal Joshy
>         Attachments: HBASE-15314.patch
>
>
> Allow bucketcache use more than just one backing file: e.g. chassis has more than one
SSD in it.



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