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From "Sean Busbey (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HBASE-10378) Divide HLog interface into User and Implementor specific interfaces
Date Sat, 25 Oct 2014 06:04:35 GMT

     [ https://issues.apache.org/jira/browse/HBASE-10378?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Sean Busbey updated HBASE-10378:
--------------------------------
    Release Note: 
HBase internals for the write ahead log have been refactored. Advanced users of HBase should
be aware of the following changes.
  - The command for analyzing write ahead logs has been renamed from 'hlog' to 'wal'. The
old usage is deprecated and will be removed in a future version.
  - Some utility methods in the HBaseTesetingUtility related to testing write-ahead-logs were
changed in incompatible ways. No functionality has been removed, but method names and arguments
have changed. See the javadoc for HBaseTestingUtility for details.
  - The labeling of server metrics on the region server status pages changed. Previously,
the number of backing files for the write ahead log was labeled 'Num. HLog Files'. If you
wish to see this statistic now, please look for the label 'Num. WAL Files.'  If you rely on
JMX for these metrics, their location has not changed.

Adding release notes in progress.

> 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-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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