[jira] [Commented] (HBASE-28216) HDFS erasure coding support for table data dirs

["Bryan Beaudreault (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-28216?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17793959#comment-17793959 ] 

Bryan Beaudreault commented on HBASE-28216:
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I’m trying to weigh two options: allow configuring EC at table level or family level. Thematically it makes sense at family level, and that would be nice for tables with families of different size. It’s also a lot more complicated to manage due to hbase directory structure of /hbase/data/namespace/table/region/family. Since family is the last component, we need to set the EC policy individually on every directory.

A table could have many thousands of regions. For example a table with 2 families and 100k regions would require setting the policy on 200k directories, and more as the table splits. 

On the other hand, if we only allow configuring on the table level then it’s just 1 directory to set it on (/hbase/data/namespace/table). 


[~weichiu] any concerns on the hdfs managing policies separately on that many directories?

> HDFS erasure coding support for table data dirs
> -----------------------------------------------
>
>                 Key: HBASE-28216
>                 URL: https://issues.apache.org/jira/browse/HBASE-28216
>             Project: HBase
>          Issue Type: New Feature
>            Reporter: Bryan Beaudreault
>            Priority: Major
>
> [Erasure coding|https://hadoop.apache.org/docs/stable/hadoop-project-dist/hadoop-hdfs/HDFSErasureCoding.html] (EC) is a hadoop-3 feature which can drastically reduce storage requirements, at the expense of locality. At my company we have a few hbase clusters which are extremely data dense and take mostly write traffic, fewer reads (cold data). We'd like to reduce the cost of these clusters, and EC is a great way to do that since it can reduce replication related storage costs by 50%.
> It's possible to enable EC policies on sub directories of HDFS. One can manually set this with {{{}hdfs ec -setPolicy -path /hbase/data/default/usertable -policy xxxx{}}}. This can work without any hbase support.
> One problem with that is a lack of visibility by operators into which tables might have EC enabled. I think this is where HBase can help. Here's my proposal:
>  * Add a new TableDescriptor and ColumnDescriptor field ERASURE_CODING_POLICY
>  * In ModifyTableProcedure preflightChecks, if ERASURE_CODING_POLICY is set, verify that the requested policy is available and enabled via DistributedFileSystem.
> getErasureCodingPolicies().
>  * During ModifyTableProcedure, add a new state for MODIFY_TABLE_SYNC_ERASURE_CODING_POLICY.
>  ** When adding or changing a policy, use DistributedFileSystem.
> setErasureCodingPolicy to sync it for the data and archive dir of that table (or column in table)
>  ** When removing the property or setting it to empty, use DistributedFileSystem.
> unsetErasureCodingPolicy to remove it from the data and archive dir.
> Since this new API is in hadoop-3 only, we'll need to add a reflection wrapper class for managing the calls and verifying that the API is available. We'll similarly do that API check in preflightChecks.



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