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From "Jonathan Hsieh (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-9426) Make custom distributed barrier procedure pluggable
Date Thu, 05 Sep 2013 23:54:52 GMT

    [ https://issues.apache.org/jira/browse/HBASE-9426?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13759641#comment-13759641
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Jonathan Hsieh commented on HBASE-9426:
---------------------------------------

I think an incremental backup or incremental snapshot would be a welcome addition to the hbase
core. 

bq. In general, the globally barriered procedure is a useful framework for implementing distributed,
coordinated functions on region servers. I think it would be good if we can invoke these custom
procedures without having to modify the HBase core.

Given your argument, I actually think the idea of having a distributed log roll or distributed
table flush built into the core makes sense. 

bq. You are right that the idea is to have an an hbase extension mechnism for 3rd party code
a la coprocessors. Since only the life-cycle management code (init/start/stop) involved, it
would still work if the procedure is changed to region-centric or table-centric.

I'm a bit more wary of opening this up for 3rd parties at the moment.  Maintaining compatibility
into the future can be quite burdensome.

Would implementing the dist log roll and dist table flush be sufficient for your use or do
they need to be tied together somehow?  Actually, an alternate implementation of snapshots
did a log roll -- see HBASE-7291.
                
> Make custom distributed barrier procedure pluggable 
> ----------------------------------------------------
>
>                 Key: HBASE-9426
>                 URL: https://issues.apache.org/jira/browse/HBASE-9426
>             Project: HBase
>          Issue Type: Improvement
>    Affects Versions: 0.95.2, 0.94.11
>            Reporter: Richard Ding
>            Assignee: Richard Ding
>
> Currently if one wants to implement a custom distributed barrier procedure (e.g., distributed
log roll or distributed table flush), the HBase core code needs to be modified in order for
the procedure to work.
> Looking into the snapshot code (especially on region server side), most of the code to
enable the procedure are generic life-cycle management (i.e., init, start, stop). We can make
this part pluggable.
> Here is the proposal. Following the coprocessor example, we define two properties:
> {code}
> hbase.procedure.regionserver.classes
> hbase.procedure.master.classes
> {code}
> The values for both are comma delimited list of classes. On region server side, the classes
implements the following interface:
> {code}
> public interface RegionServerProcedureManager {
>   public void initialize(RegionServerServices rss) throws KeeperException;
>   public void start();
>   public void stop(boolean force) throws IOException;
>   public String getProcedureName();
> }
> {code}
> While on Master side, the classes implement the interface:
> {code}
> public interface MasterProcedureManager {
>   public void initialize(MasterServices master) throws KeeperException, IOException,
UnsupportedOperationException;
>   public void stop(String why);
>   public String getProcedureName();
>   public void execProcedure(ProcedureDescription desc) throws IOException;
>   IOException;
> }
> {code}
> Where the ProcedureDescription is defined as
> {code}
> message ProcedureDescription {
>   required string name = 1;
>   required string instance = 2;
>   optional int64 creationTime = 3 [default = 0];
>   message Property {
>     required string tag = 1;
>     optional string value = 2;
>   }
>   repeated Property props = 4;
> }
> {code}
> A generic API can be defined on HMaster to trigger a procedure:
> {code}
> public boolean execProcedure(ProcedureDescription desc) throws IOException;
> {code}
> _SnapshotManager_ and _RegionServerSnapshotManager_ are special examples of _MasterProcedureManager_
and _RegionServerProcedureManager_. They will be automatically included (users don't need
to specify them in the conf file).

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