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HDFS >> mail # user >> hflush not working for me?


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Re: hflush not working for me?
Thank you for figuring it Nicholas.
St.Ack

On Fri, Oct 9, 2009 at 3:27 PM, Tsz Wo (Nicholas), Sze <
[EMAIL PROTECTED]> wrote:

> Hi St.Ack,
>
> HLog uses SequenceFile.Reader.  When a SequenceFile.Reader is constructed,
> it calls fs.getFileStatus(file).getLen().  However,
> fs.getFileStatus(file).getLen() does not return the hflushed length for
> un-closed file since the Namenode does not know the hflushed length.
> DFSClient have to ask a datanode for the length last block which is being
> written; see also HDFS-570.  That's why "hflush not working for you".  Sorry
> ...
>
> We have to change SequenceFile.Reader in order to support reading on
> unclosed SequenceFile.
>
> Nicholas
>
>
> *From:* "Tsz Wo (Nicholas), Sze" <[EMAIL PROTECTED]>
> *To:* [EMAIL PROTECTED]
> *Sent:* Fri, October 9, 2009 2:40:34 PM
>
> *Subject:* Re: hflush not working for me?
>
> Soft lease is for another writer to obtain the file lease if the original
> writer appears to abandon the file.  In the current TestReadWhileWriting
> (not counting part (c) and (d)), there is only one writer.  So soft lease is
> not related.
>
> Will check your test.
>
> Nicholas
>
>
> *From:* stack <[EMAIL PROTECTED]>
> *To:* [EMAIL PROTECTED]
> *Sent:* Fri, October 9, 2009 2:32:02 PM
> *Subject:* Re: hflush not working for me?
>
> On Fri, Oct 9, 2009 at 1:27 PM, Tsz Wo (Nicholas), Sze <
> [EMAIL PROTECTED]> wrote:
>
>> Hi St.Ack,
>>
>> > ... soft lease to 1 second ...
>> You are right that you don't have to change soft lease.  It is for append
>> but not related to hflash.
>>
>
> I should not have to set it then?  I can remove this 70 second pause in
> middle of my test?
>
>
>
>>
>> > Do I have to do open as another user?
>> This should not be necessary.
>>
>> Could you send me/post your test?
>>
>>
> Sure, as long as you don't hold this ugly code against me ever after.
>
> I checked in the code so you could try it:
> http://svn.apache.org/repos/asf/hadoop/hbase/trunk/src/test/org/apache/hadoop/hbase/regionserver/TestHLog.java
>
> Its the first test, testSync.
>
> It starts out by copying whats down in the hdfs testReadWhileWriting.  That
> bit works fine.
>
> Then comes the ugly stuff.
>
> HLog is our write-ahead log wrapper.  Internally it writes out to a
> SequenceFile.Writer.  The SequenceFile.Writer has been doctored using
> reflection so the out datamember is non-private.  A call to HLog.sync runs
> the SequenceFile.Writer.sync -- which DOES NOT call sync on the backing
> output stream -- and then it calls sync on the now accessible out stream
> (Sorry its so ugly -- I'm trying to hack stuff up fast so all of hbase gets
> access to this new facility).  If I trace in the debugger, I can see that
> the sync on the out data member goes down into hflush.  Queued up edits are
> flushed.  It seems like it should be working.
>
> Do I have to do some doctoring of the reader? (It doesn't seem so given
> that the code at the head of this test works).
>
> Thanks for taking a look Nicholas.
>
> To run the test, you can do "ant clean jar test -Dtestcase=TestHLog".
>
> (Let me know if you want an eclipse .project + .classpath so you can get it
> up in an ide to run debugger).
>
> St.Ack
>
>
>
>
>
>> Nicholas Sze
>>
>>
>> *From:* stack <[EMAIL PROTECTED]>
>> *To:* [EMAIL PROTECTED]
>> *Sent:* Fri, October 9, 2009 1:13:37 PM
>> *Subject:* hflush not working for me?
>>
>> I'm putting together some unit tests up in our application that exercise
>> hflush.  I'm using minidfscluster and a jar made by building head of the
>> 0.21 branch of hdfs (from about a minute ago).
>>
>> Code opens a file, writes a bunch of edits, invokes hflush (by calling
>> sync on DFSDataOutputStream instance) and then, without closing the Writer,
>> opens a Reader on same file.  This Reader does not see any edits not to mind
>> edits up to the sync invocation.
>>
>> I can trace the code and see how on hflush it sends the queued packets of
>> edits.
>>
>
NEW: Monitor These Apps!
elasticsearch, apache solr, apache hbase, hadoop, redis, casssandra, amazon cloudwatch, mysql, memcached, apache kafka, apache zookeeper, apache storm, ubuntu, centOS, red hat, debian, puppet labs, java, senseiDB