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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8109) HBase can manage blocks instead of files in HDFS
Date Thu, 14 Mar 2013 19:52:14 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8109?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13602632#comment-13602632
] 

Andrew Purtell commented on HBASE-8109:
---------------------------------------

bq. Once we have isolated the fs calls, we can switch to a system table tracking blocks. (that
is basically a sort of Name Node)

How would we bootstrap that block tracking system table out of a pool of blocks? Would there
be an HBase side analogue to the NN fsimage? Would we keep that state in ZK, thus making ZK
persistence critical? As a strawman I guess we could have one block containing pointers to
all blocks holding the block tracking table -- in effect, a superblock -- and we could back
this up to multiple locations like FSes do, and where today we have ZK pointing to META locations
it would point to this bootstrap inode instead. HBCK could be taught how to scan for superblocks.

A very interesting notion of building "HBaseFS".

Another option for getting the espoused benefits for compaction optimization without going
all the way to a pool of blocks: Consider an HDFS API for stitching together files? We could
get a list of blocks from the NN for a path, rewrite them independently as part of compaction
(or split), and then hand an updated list of blocks/lengths back to the NN for it to store
back into the fsimage. This would still give us the flexibility to even do (insane?) things
like share blocks between files across splits.
                
> HBase can manage blocks instead of files in HDFS
> ------------------------------------------------
>
>                 Key: HBASE-8109
>                 URL: https://issues.apache.org/jira/browse/HBASE-8109
>             Project: HBase
>          Issue Type: Brainstorming
>            Reporter: Sergey Shelukhin
>
> Prompted by previous non-Hadoop experience and some dev list discussions, and after talking
to some HDFS people about blocks.
> HBase could improve a lot by managing HDFS blocks instead of files, and reusing the blocks
among other things. Some areas that could improve are splits, compactions, management of large
blobs, locality enforcement.
> I was told that block APIs in Hadoop 2 are well-isolated, but not exposed yet. They can
easily be exposed, and as one of the first potential users we could get to help shape them.
Two areas that from my limited understanding is currently fuzzy are namespaces for blocks,
and ref-counting.
> We should come up with list of initial scenarios to figure out what we need from block
API (locality, detecting/enforcing block boundary/variable size blocks, reusing one block,
...).

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