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From "ramkrishna.s.vasudevan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-10378) Divide HLog interface into User and Implementor specific interfaces
Date Tue, 18 Nov 2014 17:44:35 GMT

    [ https://issues.apache.org/jira/browse/HBASE-10378?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14216489#comment-14216489
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ramkrishna.s.vasudevan commented on HBASE-10378:
------------------------------------------------

Still going thro the RB. One more day would be great.  In case of open region - when there
is a grouping done based on table (for eg), how are we handling the assignment of WAL to those
regions specific to a table. I am still not there in the review but that would be interesting
to see.  I am in the 5th page now.

> Divide HLog interface into User and Implementor specific interfaces
> -------------------------------------------------------------------
>
>                 Key: HBASE-10378
>                 URL: https://issues.apache.org/jira/browse/HBASE-10378
>             Project: HBase
>          Issue Type: Sub-task
>          Components: wal
>            Reporter: Himanshu Vashishtha
>            Assignee: Sean Busbey
>             Fix For: 2.0.0, 0.99.2
>
>         Attachments: 10378-1.patch, 10378-2.patch, HBASE-10378.3.patch.txt, HBASE-10378.4.patch.txt,
HBASE-10378.5.patch.txt
>
>
> HBASE-5937 introduces the HLog interface as a first step to support multiple WAL implementations.
This interface is a good start, but has some limitations/drawbacks in its current state, such
as:
> 1) There is no clear distinction b/w User and Implementor APIs, and it provides APIs
both for WAL users (append, sync, etc) and also WAL implementors (Reader/Writer interfaces,
etc). There are APIs which are very much implementation specific (getFileNum, etc) and a user
such as a RegionServer shouldn't know about it.
> 2) There are about 14 methods in FSHLog which are not present in HLog interface but are
used at several places in the unit test code. These tests typecast HLog to FSHLog, which makes
it very difficult to test multiple WAL implementations without doing some ugly checks.
> I'd like to propose some changes in HLog interface that would ease the multi WAL story:
> 1) Have two interfaces WAL and WALService. WAL provides APIs for implementors. WALService
provides APIs for users (such as RegionServer).
> 2) A skeleton implementation of the above two interface as the base class for other WAL
implementations (AbstractWAL). It provides required fields for all subclasses (fs, conf, log
dir, etc). Make a minimal set of test only methods and add this set in AbstractWAL.
> 3) HLogFactory returns a WALService reference when creating a WAL instance; if a user
need to access impl specific APIs (there are unit tests which get WAL from a HRegionServer
and then call impl specific APIs), use AbstractWAL type casting,
> 4) Make TestHLog abstract and let all implementors provide their respective test class
which extends TestHLog (TestFSHLog, for example).



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