Why LineRecordWriter.write(..) is synchronized

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Why LineRecordWriter.write(..) is synchronized

Sathwik B P
Hi,

LineRecordWriter.write(..) is synchronized. I did not find any other RecordWriter implementations define the write as synchronized.
Any specific reason for this.

regards,
sathwik
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Re: Why LineRecordWriter.write(..) is synchronized

Azuryy Yu

because we may use multi-threads to write a single file.

On Aug 8, 2013 2:54 PM, "Sathwik B P" <[hidden email]> wrote:
Hi,

LineRecordWriter.write(..) is synchronized. I did not find any other RecordWriter implementations define the write as synchronized.
Any specific reason for this.

regards,
sathwik
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Re: Why LineRecordWriter.write(..) is synchronized

Sathwik B P-2
Hi,
Thanks for your reply.
May I know where does hadoop fork multiple threads to use a single RecordWriter.

regards,
sathwik

On Thu, Aug 8, 2013 at 7:06 AM, Azuryy Yu <[hidden email]> wrote:

because we may use multi-threads to write a single file.

On Aug 8, 2013 2:54 PM, "Sathwik B P" <[hidden email]> wrote:
Hi,

LineRecordWriter.write(..) is synchronized. I did not find any other RecordWriter implementations define the write as synchronized.
Any specific reason for this.

regards,
sathwik

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Re: Why LineRecordWriter.write(..) is synchronized

Azuryy Yu

its not hadoop forked threads, we may create a line record writer, then call this writer concurrently.

On Aug 8, 2013 4:00 PM, "Sathwik B P" <[hidden email]> wrote:
Hi,
Thanks for your reply.
May I know where does hadoop fork multiple threads to use a single RecordWriter.

regards,
sathwik

On Thu, Aug 8, 2013 at 7:06 AM, Azuryy Yu <[hidden email]> wrote:

because we may use multi-threads to write a single file.

On Aug 8, 2013 2:54 PM, "Sathwik B P" <[hidden email]> wrote:
Hi,

LineRecordWriter.write(..) is synchronized. I did not find any other RecordWriter implementations define the write as synchronized.
Any specific reason for this.

regards,
sathwik

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Re: Why LineRecordWriter.write(..) is synchronized

Harsh J-2

While we don't fork by default, we do provide a MultithreadedMapper implementation that would require such synchronization. But if you are asking is it necessary, then perhaps the answer is no.

On Aug 8, 2013 3:43 PM, "Azuryy Yu" <[hidden email]> wrote:

its not hadoop forked threads, we may create a line record writer, then call this writer concurrently.

On Aug 8, 2013 4:00 PM, "Sathwik B P" <[hidden email]> wrote:
Hi,
Thanks for your reply.
May I know where does hadoop fork multiple threads to use a single RecordWriter.

regards,
sathwik

On Thu, Aug 8, 2013 at 7:06 AM, Azuryy Yu <[hidden email]> wrote:

because we may use multi-threads to write a single file.

On Aug 8, 2013 2:54 PM, "Sathwik B P" <[hidden email]> wrote:
Hi,

LineRecordWriter.write(..) is synchronized. I did not find any other RecordWriter implementations define the write as synchronized.
Any specific reason for this.

regards,
sathwik

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Re: Why LineRecordWriter.write(..) is synchronized

Niels Basjes
I may be nitpicking here but if "perhaps the answer is no" then I conclude: Perhaps the other implementations of RecordWriter are a race condition/file corruption ready to occur.


On Thu, Aug 8, 2013 at 12:50 PM, Harsh J <[hidden email]> wrote:

While we don't fork by default, we do provide a MultithreadedMapper implementation that would require such synchronization. But if you are asking is it necessary, then perhaps the answer is no.

On Aug 8, 2013 3:43 PM, "Azuryy Yu" <[hidden email]> wrote:

its not hadoop forked threads, we may create a line record writer, then call this writer concurrently.

On Aug 8, 2013 4:00 PM, "Sathwik B P" <[hidden email]> wrote:
Hi,
Thanks for your reply.
May I know where does hadoop fork multiple threads to use a single RecordWriter.

regards,
sathwik

On Thu, Aug 8, 2013 at 7:06 AM, Azuryy Yu <[hidden email]> wrote:

because we may use multi-threads to write a single file.

On Aug 8, 2013 2:54 PM, "Sathwik B P" <[hidden email]> wrote:
Hi,

LineRecordWriter.write(..) is synchronized. I did not find any other RecordWriter implementations define the write as synchronized.
Any specific reason for this.

regards,
sathwik




--
Best regards / Met vriendelijke groeten,

Niels Basjes
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Re: Why LineRecordWriter.write(..) is synchronized

jay vyas
In reply to this post by Harsh J-2
Then is this a bug?  Synchronization in absence of any race condition is normally considered "bad".

In any case id like to know why this writer is synchronized whereas the other one are not.. That is, I think, then point at issue: either other writers should be synchronized or else this one shouldn't be - consistency across the write implementations is probably desirable so that changes to output formats or record writers don't lead to bugs in multithreaded environments .

On Aug 8, 2013, at 6:50 AM, Harsh J <[hidden email]> wrote:

While we don't fork by default, we do provide a MultithreadedMapper implementation that would require such synchronization. But if you are asking is it necessary, then perhaps the answer is no.

On Aug 8, 2013 3:43 PM, "Azuryy Yu" <[hidden email]> wrote:

its not hadoop forked threads, we may create a line record writer, then call this writer concurrently.

On Aug 8, 2013 4:00 PM, "Sathwik B P" <[hidden email]> wrote:
Hi,
Thanks for your reply.
May I know where does hadoop fork multiple threads to use a single RecordWriter.

regards,
sathwik

On Thu, Aug 8, 2013 at 7:06 AM, Azuryy Yu <[hidden email]> wrote:

because we may use multi-threads to write a single file.

On Aug 8, 2013 2:54 PM, "Sathwik B P" <[hidden email]> wrote:
Hi,

LineRecordWriter.write(..) is synchronized. I did not find any other RecordWriter implementations define the write as synchronized.
Any specific reason for this.

regards,
sathwik

jay vyas
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Re: Why LineRecordWriter.write(..) is synchronized

Sathwik B P
Hi Harsh,

Do you want me to raise a Jira on this.

regards,
sathwik

On Thu, Aug 8, 2013 at 5:23 PM, Jay Vyas <[hidden email]> wrote:
Then is this a bug?  Synchronization in absence of any race condition is normally considered "bad".

In any case id like to know why this writer is synchronized whereas the other one are not.. That is, I think, then point at issue: either other writers should be synchronized or else this one shouldn't be - consistency across the write implementations is probably desirable so that changes to output formats or record writers don't lead to bugs in multithreaded environments .

On Aug 8, 2013, at 6:50 AM, Harsh J <[hidden email]> wrote:

While we don't fork by default, we do provide a MultithreadedMapper implementation that would require such synchronization. But if you are asking is it necessary, then perhaps the answer is no.

On Aug 8, 2013 3:43 PM, "Azuryy Yu" <[hidden email]> wrote:

its not hadoop forked threads, we may create a line record writer, then call this writer concurrently.

On Aug 8, 2013 4:00 PM, "Sathwik B P" <[hidden email]> wrote:
Hi,
Thanks for your reply.
May I know where does hadoop fork multiple threads to use a single RecordWriter.

regards,
sathwik

On Thu, Aug 8, 2013 at 7:06 AM, Azuryy Yu <[hidden email]> wrote:

because we may use multi-threads to write a single file.

On Aug 8, 2013 2:54 PM, "Sathwik B P" <[hidden email]> wrote:
Hi,

LineRecordWriter.write(..) is synchronized. I did not find any other RecordWriter implementations define the write as synchronized.
Any specific reason for this.

regards,
sathwik


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Re: Why LineRecordWriter.write(..) is synchronized

Niels Basjes
I would say yes make this a Jira.
The actual change can fall (as proposed by Jay) in two directions: Put in synchronization in all implementations OR take it out of all implementations.

I think the first thing to determine is why the synchronization was put into the  LineRecordWriter in the first place.


The oldest I have been able to find is a commit on 2009-05-18 for HADOOP-4687 that is about moving stuff around (i.e. this code is even older than that).

Niels 



On Thu, Aug 8, 2013 at 2:21 PM, Sathwik B P <[hidden email]> wrote:
Hi Harsh,

Do you want me to raise a Jira on this.

regards,
sathwik


On Thu, Aug 8, 2013 at 5:23 PM, Jay Vyas <[hidden email]> wrote:
Then is this a bug?  Synchronization in absence of any race condition is normally considered "bad".

In any case id like to know why this writer is synchronized whereas the other one are not.. That is, I think, then point at issue: either other writers should be synchronized or else this one shouldn't be - consistency across the write implementations is probably desirable so that changes to output formats or record writers don't lead to bugs in multithreaded environments .

On Aug 8, 2013, at 6:50 AM, Harsh J <[hidden email]> wrote:

While we don't fork by default, we do provide a MultithreadedMapper implementation that would require such synchronization. But if you are asking is it necessary, then perhaps the answer is no.

On Aug 8, 2013 3:43 PM, "Azuryy Yu" <[hidden email]> wrote:

its not hadoop forked threads, we may create a line record writer, then call this writer concurrently.

On Aug 8, 2013 4:00 PM, "Sathwik B P" <[hidden email]> wrote:
Hi,
Thanks for your reply.
May I know where does hadoop fork multiple threads to use a single RecordWriter.

regards,
sathwik

On Thu, Aug 8, 2013 at 7:06 AM, Azuryy Yu <[hidden email]> wrote:

because we may use multi-threads to write a single file.

On Aug 8, 2013 2:54 PM, "Sathwik B P" <[hidden email]> wrote:
Hi,

LineRecordWriter.write(..) is synchronized. I did not find any other RecordWriter implementations define the write as synchronized.
Any specific reason for this.

regards,
sathwik





--
Best regards / Met vriendelijke groeten,

Niels Basjes
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Re: Why LineRecordWriter.write(..) is synchronized

Azuryy Yu
In reply to this post by jay vyas

sequence writer is also synchronized, I dont think this is bad.

if you call HDFS api to write concurrently, then its necessary.

On Aug 8, 2013 7:53 PM, "Jay Vyas" <[hidden email]> wrote:
Then is this a bug?  Synchronization in absence of any race condition is normally considered "bad".

In any case id like to know why this writer is synchronized whereas the other one are not.. That is, I think, then point at issue: either other writers should be synchronized or else this one shouldn't be - consistency across the write implementations is probably desirable so that changes to output formats or record writers don't lead to bugs in multithreaded environments .

On Aug 8, 2013, at 6:50 AM, Harsh J <[hidden email]> wrote:

While we don't fork by default, we do provide a MultithreadedMapper implementation that would require such synchronization. But if you are asking is it necessary, then perhaps the answer is no.

On Aug 8, 2013 3:43 PM, "Azuryy Yu" <[hidden email]> wrote:

its not hadoop forked threads, we may create a line record writer, then call this writer concurrently.

On Aug 8, 2013 4:00 PM, "Sathwik B P" <[hidden email]> wrote:
Hi,
Thanks for your reply.
May I know where does hadoop fork multiple threads to use a single RecordWriter.

regards,
sathwik

On Thu, Aug 8, 2013 at 7:06 AM, Azuryy Yu <[hidden email]> wrote:

because we may use multi-threads to write a single file.

On Aug 8, 2013 2:54 PM, "Sathwik B P" <[hidden email]> wrote:
Hi,

LineRecordWriter.write(..) is synchronized. I did not find any other RecordWriter implementations define the write as synchronized.
Any specific reason for this.

regards,
sathwik

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Re: Why LineRecordWriter.write(..) is synchronized

Harsh J-2
I suppose I should have been clearer. There's no problem out of box if
people stick to the libraries we offer :)

Yes the LRW was marked synchronized at some point over 8 years ago [1]
in support for multi-threaded maps, but the framework has changed much
since then. The MultithreadedMapper/etc. API we offer now
automatically shields the devs away from having to think of output
thread safety [2].

I can imagine there can only be a problem if a user writes their own
unsafe multi threaded task. I suppose we could document that in the
Mapper/MapRunner and Reducer APIs.

[1] - http://svn.apache.org/viewvc?view=revision&revision=171186 -
Commit added a synchronized to the write call.
[2] - MultiThreadedMapper/etc. synchronize over the collector -
http://svn.apache.org/viewvc/hadoop/common/trunk/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/lib/map/MultithreadedMapper.java?view=markup

On Thu, Aug 8, 2013 at 7:52 PM, Azuryy Yu <[hidden email]> wrote:

> sequence writer is also synchronized, I dont think this is bad.
>
> if you call HDFS api to write concurrently, then its necessary.
>
> On Aug 8, 2013 7:53 PM, "Jay Vyas" <[hidden email]> wrote:
>>
>> Then is this a bug?  Synchronization in absence of any race condition is
>> normally considered "bad".
>>
>> In any case id like to know why this writer is synchronized whereas the
>> other one are not.. That is, I think, then point at issue: either other
>> writers should be synchronized or else this one shouldn't be - consistency
>> across the write implementations is probably desirable so that changes to
>> output formats or record writers don't lead to bugs in multithreaded
>> environments .
>>
>> On Aug 8, 2013, at 6:50 AM, Harsh J <[hidden email]> wrote:
>>
>> While we don't fork by default, we do provide a MultithreadedMapper
>> implementation that would require such synchronization. But if you are
>> asking is it necessary, then perhaps the answer is no.
>>
>> On Aug 8, 2013 3:43 PM, "Azuryy Yu" <[hidden email]> wrote:
>>>
>>> its not hadoop forked threads, we may create a line record writer, then
>>> call this writer concurrently.
>>>
>>> On Aug 8, 2013 4:00 PM, "Sathwik B P" <[hidden email]> wrote:
>>>>
>>>> Hi,
>>>> Thanks for your reply.
>>>> May I know where does hadoop fork multiple threads to use a single
>>>> RecordWriter.
>>>>
>>>> regards,
>>>> sathwik
>>>>
>>>> On Thu, Aug 8, 2013 at 7:06 AM, Azuryy Yu <[hidden email]> wrote:
>>>>>
>>>>> because we may use multi-threads to write a single file.
>>>>>
>>>>> On Aug 8, 2013 2:54 PM, "Sathwik B P" <[hidden email]> wrote:
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> LineRecordWriter.write(..) is synchronized. I did not find any other
>>>>>> RecordWriter implementations define the write as synchronized.
>>>>>> Any specific reason for this.
>>>>>>
>>>>>> regards,
>>>>>> sathwik
>>>>
>>>>
>



--
Harsh J
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Re: Why LineRecordWriter.write(..) is synchronized

Sathwik B P-2
Hi Harsh,

Does it make any sense to keep the method in LRW still synchronized. Isn't it creating unnecessary overhead for non multi threaded implementations.

regards,
sathwik

On Fri, Aug 9, 2013 at 7:16 AM, Harsh J <[hidden email]> wrote:
I suppose I should have been clearer. There's no problem out of box if
people stick to the libraries we offer :)

Yes the LRW was marked synchronized at some point over 8 years ago [1]
in support for multi-threaded maps, but the framework has changed much
since then. The MultithreadedMapper/etc. API we offer now
automatically shields the devs away from having to think of output
thread safety [2].

I can imagine there can only be a problem if a user writes their own
unsafe multi threaded task. I suppose we could document that in the
Mapper/MapRunner and Reducer APIs.

[1] - http://svn.apache.org/viewvc?view=revision&revision=171186 -
Commit added a synchronized to the write call.
[2] - MultiThreadedMapper/etc. synchronize over the collector -
http://svn.apache.org/viewvc/hadoop/common/trunk/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/lib/map/MultithreadedMapper.java?view=markup

On Thu, Aug 8, 2013 at 7:52 PM, Azuryy Yu <[hidden email]> wrote:
> sequence writer is also synchronized, I dont think this is bad.
>
> if you call HDFS api to write concurrently, then its necessary.
>
> On Aug 8, 2013 7:53 PM, "Jay Vyas" <[hidden email]> wrote:
>>
>> Then is this a bug?  Synchronization in absence of any race condition is
>> normally considered "bad".
>>
>> In any case id like to know why this writer is synchronized whereas the
>> other one are not.. That is, I think, then point at issue: either other
>> writers should be synchronized or else this one shouldn't be - consistency
>> across the write implementations is probably desirable so that changes to
>> output formats or record writers don't lead to bugs in multithreaded
>> environments .
>>
>> On Aug 8, 2013, at 6:50 AM, Harsh J <[hidden email]> wrote:
>>
>> While we don't fork by default, we do provide a MultithreadedMapper
>> implementation that would require such synchronization. But if you are
>> asking is it necessary, then perhaps the answer is no.
>>
>> On Aug 8, 2013 3:43 PM, "Azuryy Yu" <[hidden email]> wrote:
>>>
>>> its not hadoop forked threads, we may create a line record writer, then
>>> call this writer concurrently.
>>>
>>> On Aug 8, 2013 4:00 PM, "Sathwik B P" <[hidden email]> wrote:
>>>>
>>>> Hi,
>>>> Thanks for your reply.
>>>> May I know where does hadoop fork multiple threads to use a single
>>>> RecordWriter.
>>>>
>>>> regards,
>>>> sathwik
>>>>
>>>> On Thu, Aug 8, 2013 at 7:06 AM, Azuryy Yu <[hidden email]> wrote:
>>>>>
>>>>> because we may use multi-threads to write a single file.
>>>>>
>>>>> On Aug 8, 2013 2:54 PM, "Sathwik B P" <[hidden email]> wrote:
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> LineRecordWriter.write(..) is synchronized. I did not find any other
>>>>>> RecordWriter implementations define the write as synchronized.
>>>>>> Any specific reason for this.
>>>>>>
>>>>>> regards,
>>>>>> sathwik
>>>>
>>>>
>



--
Harsh J

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Re: Why LineRecordWriter.write(..) is synchronized

Harsh J-2
Yes, I feel we could discuss this over a JIRA to remove it if it hurts
perf. too much, but it would have to be a marked incompatible change,
and we have to add a note about the lack of thread safety in the
javadoc of base Mapper/Reducer classes.

On Sun, Aug 11, 2013 at 1:26 PM, Sathwik B P <[hidden email]> wrote:

> Hi Harsh,
>
> Does it make any sense to keep the method in LRW still synchronized. Isn't
> it creating unnecessary overhead for non multi threaded implementations.
>
> regards,
> sathwik
>
>
> On Fri, Aug 9, 2013 at 7:16 AM, Harsh J <[hidden email]> wrote:
>>
>> I suppose I should have been clearer. There's no problem out of box if
>> people stick to the libraries we offer :)
>>
>> Yes the LRW was marked synchronized at some point over 8 years ago [1]
>> in support for multi-threaded maps, but the framework has changed much
>> since then. The MultithreadedMapper/etc. API we offer now
>> automatically shields the devs away from having to think of output
>> thread safety [2].
>>
>> I can imagine there can only be a problem if a user writes their own
>> unsafe multi threaded task. I suppose we could document that in the
>> Mapper/MapRunner and Reducer APIs.
>>
>> [1] - http://svn.apache.org/viewvc?view=revision&revision=171186 -
>> Commit added a synchronized to the write call.
>> [2] - MultiThreadedMapper/etc. synchronize over the collector -
>>
>> http://svn.apache.org/viewvc/hadoop/common/trunk/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/lib/map/MultithreadedMapper.java?view=markup
>>
>> On Thu, Aug 8, 2013 at 7:52 PM, Azuryy Yu <[hidden email]> wrote:
>> > sequence writer is also synchronized, I dont think this is bad.
>> >
>> > if you call HDFS api to write concurrently, then its necessary.
>> >
>> > On Aug 8, 2013 7:53 PM, "Jay Vyas" <[hidden email]> wrote:
>> >>
>> >> Then is this a bug?  Synchronization in absence of any race condition
>> >> is
>> >> normally considered "bad".
>> >>
>> >> In any case id like to know why this writer is synchronized whereas the
>> >> other one are not.. That is, I think, then point at issue: either other
>> >> writers should be synchronized or else this one shouldn't be -
>> >> consistency
>> >> across the write implementations is probably desirable so that changes
>> >> to
>> >> output formats or record writers don't lead to bugs in multithreaded
>> >> environments .
>> >>
>> >> On Aug 8, 2013, at 6:50 AM, Harsh J <[hidden email]> wrote:
>> >>
>> >> While we don't fork by default, we do provide a MultithreadedMapper
>> >> implementation that would require such synchronization. But if you are
>> >> asking is it necessary, then perhaps the answer is no.
>> >>
>> >> On Aug 8, 2013 3:43 PM, "Azuryy Yu" <[hidden email]> wrote:
>> >>>
>> >>> its not hadoop forked threads, we may create a line record writer,
>> >>> then
>> >>> call this writer concurrently.
>> >>>
>> >>> On Aug 8, 2013 4:00 PM, "Sathwik B P" <[hidden email]> wrote:
>> >>>>
>> >>>> Hi,
>> >>>> Thanks for your reply.
>> >>>> May I know where does hadoop fork multiple threads to use a single
>> >>>> RecordWriter.
>> >>>>
>> >>>> regards,
>> >>>> sathwik
>> >>>>
>> >>>> On Thu, Aug 8, 2013 at 7:06 AM, Azuryy Yu <[hidden email]> wrote:
>> >>>>>
>> >>>>> because we may use multi-threads to write a single file.
>> >>>>>
>> >>>>> On Aug 8, 2013 2:54 PM, "Sathwik B P" <[hidden email]> wrote:
>> >>>>>>
>> >>>>>> Hi,
>> >>>>>>
>> >>>>>> LineRecordWriter.write(..) is synchronized. I did not find any
>> >>>>>> other
>> >>>>>> RecordWriter implementations define the write as synchronized.
>> >>>>>> Any specific reason for this.
>> >>>>>>
>> >>>>>> regards,
>> >>>>>> sathwik
>> >>>>
>> >>>>
>> >
>>
>>
>>
>> --
>> Harsh J
>
>



--
Harsh J
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Re: Why LineRecordWriter.write(..) is synchronized

Niels Basjes

I expect the impact on the IO speed to be almost 0 because waiting for a single disk seek is longer than many thousands of calls to a synchronized method.

Niels

On Aug 11, 2013 3:00 PM, "Harsh J" <[hidden email]> wrote:
Yes, I feel we could discuss this over a JIRA to remove it if it hurts
perf. too much, but it would have to be a marked incompatible change,
and we have to add a note about the lack of thread safety in the
javadoc of base Mapper/Reducer classes.

On Sun, Aug 11, 2013 at 1:26 PM, Sathwik B P <[hidden email]> wrote:
> Hi Harsh,
>
> Does it make any sense to keep the method in LRW still synchronized. Isn't
> it creating unnecessary overhead for non multi threaded implementations.
>
> regards,
> sathwik
>
>
> On Fri, Aug 9, 2013 at 7:16 AM, Harsh J <[hidden email]> wrote:
>>
>> I suppose I should have been clearer. There's no problem out of box if
>> people stick to the libraries we offer :)
>>
>> Yes the LRW was marked synchronized at some point over 8 years ago [1]
>> in support for multi-threaded maps, but the framework has changed much
>> since then. The MultithreadedMapper/etc. API we offer now
>> automatically shields the devs away from having to think of output
>> thread safety [2].
>>
>> I can imagine there can only be a problem if a user writes their own
>> unsafe multi threaded task. I suppose we could document that in the
>> Mapper/MapRunner and Reducer APIs.
>>
>> [1] - http://svn.apache.org/viewvc?view=revision&revision=171186 -
>> Commit added a synchronized to the write call.
>> [2] - MultiThreadedMapper/etc. synchronize over the collector -
>>
>> http://svn.apache.org/viewvc/hadoop/common/trunk/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/lib/map/MultithreadedMapper.java?view=markup
>>
>> On Thu, Aug 8, 2013 at 7:52 PM, Azuryy Yu <[hidden email]> wrote:
>> > sequence writer is also synchronized, I dont think this is bad.
>> >
>> > if you call HDFS api to write concurrently, then its necessary.
>> >
>> > On Aug 8, 2013 7:53 PM, "Jay Vyas" <[hidden email]> wrote:
>> >>
>> >> Then is this a bug?  Synchronization in absence of any race condition
>> >> is
>> >> normally considered "bad".
>> >>
>> >> In any case id like to know why this writer is synchronized whereas the
>> >> other one are not.. That is, I think, then point at issue: either other
>> >> writers should be synchronized or else this one shouldn't be -
>> >> consistency
>> >> across the write implementations is probably desirable so that changes
>> >> to
>> >> output formats or record writers don't lead to bugs in multithreaded
>> >> environments .
>> >>
>> >> On Aug 8, 2013, at 6:50 AM, Harsh J <[hidden email]> wrote:
>> >>
>> >> While we don't fork by default, we do provide a MultithreadedMapper
>> >> implementation that would require such synchronization. But if you are
>> >> asking is it necessary, then perhaps the answer is no.
>> >>
>> >> On Aug 8, 2013 3:43 PM, "Azuryy Yu" <[hidden email]> wrote:
>> >>>
>> >>> its not hadoop forked threads, we may create a line record writer,
>> >>> then
>> >>> call this writer concurrently.
>> >>>
>> >>> On Aug 8, 2013 4:00 PM, "Sathwik B P" <[hidden email]> wrote:
>> >>>>
>> >>>> Hi,
>> >>>> Thanks for your reply.
>> >>>> May I know where does hadoop fork multiple threads to use a single
>> >>>> RecordWriter.
>> >>>>
>> >>>> regards,
>> >>>> sathwik
>> >>>>
>> >>>> On Thu, Aug 8, 2013 at 7:06 AM, Azuryy Yu <[hidden email]> wrote:
>> >>>>>
>> >>>>> because we may use multi-threads to write a single file.
>> >>>>>
>> >>>>> On Aug 8, 2013 2:54 PM, "Sathwik B P" <[hidden email]> wrote:
>> >>>>>>
>> >>>>>> Hi,
>> >>>>>>
>> >>>>>> LineRecordWriter.write(..) is synchronized. I did not find any
>> >>>>>> other
>> >>>>>> RecordWriter implementations define the write as synchronized.
>> >>>>>> Any specific reason for this.
>> >>>>>>
>> >>>>>> regards,
>> >>>>>> sathwik
>> >>>>
>> >>>>
>> >
>>
>>
>>
>> --
>> Harsh J
>
>



--
Harsh J