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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-12498) Integrate HydraBase RMap in RegionManager
Date Thu, 04 Dec 2014 20:07:12 GMT

    [ https://issues.apache.org/jira/browse/HBASE-12498?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14234561#comment-14234561

stack commented on HBASE-12498:

I like it that master continues to tell regionservers what they should serve.  Thanks [~amitanand]

> Integrate HydraBase RMap in RegionManager
> -----------------------------------------
>                 Key: HBASE-12498
>                 URL: https://issues.apache.org/jira/browse/HBASE-12498
>             Project: HBase
>          Issue Type: Sub-task
>          Components: master, Region Assignment
>            Reporter: Rishit Shroff
>            Assignee: Amitanand Aiyer
> We need to integrate the idea of RMap (Global Region Locator) into HBase.
> RMap:
> In Hydrabase, we wanted to avoid having special tables that require to be online and
available, before other servers can start processing their regions. To this end, in hydrabase,
we use a notion of RMap — that tells the servers which regions to open; and also servers
as a look up place for the clients to discover the set of servers handling a particular region.
> This RMap is stored in a well known path, as specified in the configuration. Upon initialization,
RegionServers read this file and determine the set of regions that it needs to open; and the
set of peers that it expects to hear from for each of those regions.
> Since RMap is stored in HDFS, the only way to change it is to create a new HDFS file
and update the servers about it. This is intended to be a not-so-common operation; however,
this may be required when a new machine joins the service, or an existing machine needs to
be taken away for a significant amount of time to perform maintenance.
> We run a daemon, every 15 minutes, (currently in the master) to determine the set of
machines going to repair and vice versa; and update the RMap accordingly.
> 1. In the current hydraBase model, updating the RMap is done by a single daemon; while
every region server individually reads and updates itself accordingly.
> 2. OSS HBase seems to be using a model where a dedicated master/server manager is responsible
for coordinating the regions that should be opened/served by each region server. Region servers
simply follow the instructions received from the server manager. 
> With respect to integrating both. We plan to use the servermanager to read the RMap and
coordinate the region opens on various regionservers. RMap will be still stored as a HDFS
file, that will be read by the ServerManager/Master to assign regions.

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