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From "chunhui shen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-15314) Allow more than one backing file in bucketcache
Date Wed, 25 Jan 2017 03:03:26 GMT

    [ https://issues.apache.org/jira/browse/HBASE-15314?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15837087#comment-15837087

chunhui shen commented on HBASE-15314:

bq.but at least we can guarantee that every allocation will reside in its own file
I also have considered this scene, but seems not meaningful :
1. It will take an extra IO if  an allocation cross files, but the probability is about 32KB/320GB
≈ 1/10M ( example for block size 32KB, one file capacity 320GB).  So,  I think it's no effect
for perfomance
2. With crossing files allocation, no extra logic is needed if a single file fails due to
an IO error.  We will free the whole alloction if failed ( see this logic from BucketCahe#writeToCache).

In addition,  it seems introducing an odd stuff which is not understandable easily for user
, from the release notes:
The first block is wasted (it is marked allocated). The worst case is 1 'largest block' per
file. If an allocation fails for any reason, all/any allocated blocks (including wasted ones)
are freed again for subsequent allocation requests. This is very similar to a 'JBOD' configuration
(there is no striping of any kind).

> 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: Aaron Tokhy
>         Attachments: FileIOEngine.java, HBASE-15314.master.001.patch, HBASE-15314.master.001.patch,
HBASE-15314.patch, HBASE-15314-v2.patch, HBASE-15314-v3.patch
> Allow bucketcache use more than just one backing file: e.g. chassis has more than one
SSD in it.

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