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Date: Sat, 22 Sep 2012 03:21:08 +1100 (NCT)
From: "Flavio Junqueira (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
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Subject: [jira] [Commented] (HBASE-5937) Refactor HLog into an interface.
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    [ https://issues.apache.org/jira/browse/HBASE-5937?page=3Dcom.atlassian=
.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=3D1346=
0592#comment-13460592 ]=20

Flavio Junqueira commented on HBASE-5937:
-----------------------------------------

Thanks for responding, Stack.

bq. Sorry for not getting to your log. What have you been having to do to g=
et tests to pass? How did you fix TestMultiParallel? It is stuff to do w/ t=
his refactoring?

It was our bug.

bq.  Currently Reader and Writer are Interfaces defined inside HLog. You ge=
t one by calling a static method on HLog. You'd like to getReader non-stati=
c, an invocation on a particular instance of HLog.
bq. That seems fine by me. It makes sense given what you are trying to do. =
It is less flexible than what we currently have but its flexible because it=
 presumes a particular implementation of HLog.

It is simpler to leave getReader and getWriter as static methods. Given tha=
t a reader/writer is for a concrete WAL, Ivan and I thought that it would b=
e best to have these methods available as instance methods. However, it is =
not looking simple to implement because we don't have HLog objects availabl=
e in all places we need a reader or a writer, and the initialization of HLo=
g objects makes it tricky to instantiate it only to get a reader or a write=
r. At this point, I'm tempted to leave them as static methods for now, unle=
ss anyone has a strong preference otherwise.

bq. I hope you call your HLog Inteface WAL!

It is fine with me to make the change.

bq. I think this work trying to make an Interface for WAL is kinda importan=
t. There is this bookeeping project but the multi-WAL dev =E2=80=93 i.e. ma=
king the regionserver write more than one WAL at a time (into HDFS) =E2=80=
=93 could use the result of this effort too.

BookKeeper provides the ability to write multiple concurrent logs, but if t=
he regionserver code is not prepared, then we won't be able to benefit from=
 this feature. Consequently, it does sound very important to have the regio=
nserver writing to more than one WAL at a time.

Currently there is one test failing consistently for me:

{noformat}
org.apache.hadoop.hbase.TestLocalHBaseCluster
{noformat}

and I believe the culprit is this:

{noformat}
WARNING! File system needs to be upgraded.  You have version null and I wan=
t version 7.  Run the '${HBASE_HOME}/bin/hbase migrate' script.
2012-09-21 17:27:06,075 FATAL [Master:0;perfectsalt-lm.barcelona.corp.yahoo=
.com,52906,1348241225714] master.HMaster(1838): Unhandled exception. Starti=
ng shutdown.
org.apache.hadoop.hbase.util.FileSystemVersionException: File system needs =
to be upgraded.  You have version null and I want version 7.  Run the '${HB=
ASE_HOME}/bin/hbase migrate' script.
{noformat}

Any clue of why this could be happening?
               =20
> Refactor HLog into an interface.
> --------------------------------
>
>                 Key: HBASE-5937
>                 URL: https://issues.apache.org/jira/browse/HBASE-5937
>             Project: HBase
>          Issue Type: Sub-task
>            Reporter: Li Pi
>            Assignee: Flavio Junqueira
>            Priority: Minor
>         Attachments: org.apache.hadoop.hbase.client.TestMultiParallel-out=
put.txt
>
>
> What the summary says. Create HLog interface. Make current implementation=
 use it.

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