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https://issues.apache.org/jira/browse/HBASE-10378?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13877189#comment-13877189
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ramkrishna.s.vasudevan commented on HBASE-10378:
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We could discuss offline too, not an issue. and then consolidate our thoughts
here.
>bq.Or, have the grouping logic in WAL impl and rewrite the getWAL to use this
>grouping knowledge? i.e., getWAL passes a Hregioninfo to the underlying
>Group-WAL-impl, and the underlying Group-wal impl returns a WALService
>instance based on its grouping.
I would prefer this. Let HRS not deal with these things. The HRS at any point
of time should only say instantiate WAL and based on what grouping or mechanism
we select those many HLogs should be instantiated and the supporting feature
like syncer,writers and replication for every HLog should be done inside the
Group-WAL impl.
Another API which I was not sure how to go about was the rollWriter() called
from admin. Currently it returns set of regions that were flushed on calling
rollWriter.
Now it should be an array of regions or a list of regions. We can discuss
offline, fine with it.
> 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
> Attachments: 10378-1.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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