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Posted to common-user@hadoop.apache.org by Alex Feinberg <al...@socialmedia.com> on 2008/09/19 06:15:10 UTC
Data corruption when using Lzo Codec
Hello,
I am running a custom crawler (written internally) using hadoop
streaming. I am attempting to
compress the output using LZO, but instead I am receiving corrupted
output that is neither in the
format I am aiming for nor as a compressed lzo file. Is this a known
issue? Is there anything
I am doing inherently wrong?
Here is the command line I am using:
~/hadoop/bin/hadoop jar
/home/hadoop/hadoop/contrib/streaming/hadoop-0.17.2.1-streaming.jar
-inputformat org.apache.hadoop.mapred.SequenceFileAsTextInputFormat
-mapper /home/hadoop/crawl_map -reducer NONE -jobconf
mapred.output.compress=true -jobconf
mapred.output.compression.codec=org.apache.hadoop.io.compress.LzoCodec
-input pages -output crawl.lzo -jobconf mapred.reduce.tasks=0
The input is in in form of URLs stored as a SequenceFile
When running this without LZO compression, no such issue occurs.
Is there any way for me to recover the corrupted data as to be able to
process it by other
hadoop jobs or offline?
Thanks,
--
Alex Feinberg
Platform Engineer, SocialMedia Networks
Re: Data corruption when using Lzo Codec
Posted by Chris Douglas <ch...@yahoo-inc.com>.
If you're using TextInputFormat, you need to add LzoCodec to the list
of codecs in the io.compression.codecs property.
LzopCodec is only for reading/writing files produced/consumed by the C
tool; it's not in 0.17. The ".lzo" files produced in 0.17 are not
"real" .lzo files, but that's how you can get the codec to recognize
them in this version. In the future, you might want to just use the
lzo codec with SequenceFileOutputFormat (use BLOCK compression). -C
On Sep 19, 2008, at 8:46 AM, Alex Feinberg wrote:
> Hi Chris,
>
> I was also unable to decompress by simply doing a map/reducer with
> "cat"
> as a mapper and then doing dfs -get either.
>
> I will try using LzopCodec.
>
> Thanks,
> - Alex
>
> On Fri, Sep 19, 2008 at 2:34 AM, Chris Douglas <chrisdo@yahoo-
> inc.com> wrote:
>> It's probably not corrupted. If by "compressed lzo file" you mean
>> something
>> readable with lzop, you should use LzopCodec, not LzoCodec.
>> LzoCodec doesn't
>> write header information required by that tool.
>>
>> Guessing at the output format (length encoded blocks of data
>> compressed by
>> the lzo algorithm), it's probably readable by TextInputFormat, but
>> YMMV. If
>> you wanted to use the C tool, you'll have to add the appropriate
>> header (see
>> lzop source or LzopCodec) using a hex editor and four zero bytes to
>> the end
>> of the file. You can also use lzo compression in SequenceFiles. -C
>>
>> On Sep 18, 2008, at 9:15 PM, Alex Feinberg wrote:
>>
>>> Hello,
>>>
>>> I am running a custom crawler (written internally) using hadoop
>>> streaming. I am attempting to
>>> compress the output using LZO, but instead I am receiving corrupted
>>> output that is neither in the
>>> format I am aiming for nor as a compressed lzo file. Is this a known
>>> issue? Is there anything
>>> I am doing inherently wrong?
>>>
>>> Here is the command line I am using:
>>>
>>> ~/hadoop/bin/hadoop jar
>>> /home/hadoop/hadoop/contrib/streaming/hadoop-0.17.2.1-streaming.jar
>>> -inputformat org.apache.hadoop.mapred.SequenceFileAsTextInputFormat
>>> -mapper /home/hadoop/crawl_map -reducer NONE -jobconf
>>> mapred.output.compress=true -jobconf
>>> mapred
>>> .output.compression.codec=org.apache.hadoop.io.compress.LzoCodec
>>> -input pages -output crawl.lzo -jobconf mapred.reduce.tasks=0
>>>
>>> The input is in in form of URLs stored as a SequenceFile
>>>
>>> When running this without LZO compression, no such issue occurs.
>>>
>>> Is there any way for me to recover the corrupted data as to be
>>> able to
>>> process it by other
>>> hadoop jobs or offline?
>>>
>>> Thanks,
>>>
>>> --
>>> Alex Feinberg
>>> Platform Engineer, SocialMedia Networks
>>
>>
>
>
>
> --
> Alex Feinberg
> Platform Engineer, SocialMedia Networks
Re: Data corruption when using Lzo Codec
Posted by Alex Feinberg <al...@socialmedia.com>.
Hi Chris,
I was also unable to decompress by simply doing a map/reducer with "cat"
as a mapper and then doing dfs -get either.
I will try using LzopCodec.
Thanks,
- Alex
On Fri, Sep 19, 2008 at 2:34 AM, Chris Douglas <ch...@yahoo-inc.com> wrote:
> It's probably not corrupted. If by "compressed lzo file" you mean something
> readable with lzop, you should use LzopCodec, not LzoCodec. LzoCodec doesn't
> write header information required by that tool.
>
> Guessing at the output format (length encoded blocks of data compressed by
> the lzo algorithm), it's probably readable by TextInputFormat, but YMMV. If
> you wanted to use the C tool, you'll have to add the appropriate header (see
> lzop source or LzopCodec) using a hex editor and four zero bytes to the end
> of the file. You can also use lzo compression in SequenceFiles. -C
>
> On Sep 18, 2008, at 9:15 PM, Alex Feinberg wrote:
>
>> Hello,
>>
>> I am running a custom crawler (written internally) using hadoop
>> streaming. I am attempting to
>> compress the output using LZO, but instead I am receiving corrupted
>> output that is neither in the
>> format I am aiming for nor as a compressed lzo file. Is this a known
>> issue? Is there anything
>> I am doing inherently wrong?
>>
>> Here is the command line I am using:
>>
>> ~/hadoop/bin/hadoop jar
>> /home/hadoop/hadoop/contrib/streaming/hadoop-0.17.2.1-streaming.jar
>> -inputformat org.apache.hadoop.mapred.SequenceFileAsTextInputFormat
>> -mapper /home/hadoop/crawl_map -reducer NONE -jobconf
>> mapred.output.compress=true -jobconf
>> mapred.output.compression.codec=org.apache.hadoop.io.compress.LzoCodec
>> -input pages -output crawl.lzo -jobconf mapred.reduce.tasks=0
>>
>> The input is in in form of URLs stored as a SequenceFile
>>
>> When running this without LZO compression, no such issue occurs.
>>
>> Is there any way for me to recover the corrupted data as to be able to
>> process it by other
>> hadoop jobs or offline?
>>
>> Thanks,
>>
>> --
>> Alex Feinberg
>> Platform Engineer, SocialMedia Networks
>
>
--
Alex Feinberg
Platform Engineer, SocialMedia Networks
Re: Data corruption when using Lzo Codec
Posted by Chris Douglas <ch...@yahoo-inc.com>.
It's probably not corrupted. If by "compressed lzo file" you mean
something readable with lzop, you should use LzopCodec, not LzoCodec.
LzoCodec doesn't write header information required by that tool.
Guessing at the output format (length encoded blocks of data
compressed by the lzo algorithm), it's probably readable by
TextInputFormat, but YMMV. If you wanted to use the C tool, you'll
have to add the appropriate header (see lzop source or LzopCodec)
using a hex editor and four zero bytes to the end of the file. You can
also use lzo compression in SequenceFiles. -C
On Sep 18, 2008, at 9:15 PM, Alex Feinberg wrote:
> Hello,
>
> I am running a custom crawler (written internally) using hadoop
> streaming. I am attempting to
> compress the output using LZO, but instead I am receiving corrupted
> output that is neither in the
> format I am aiming for nor as a compressed lzo file. Is this a known
> issue? Is there anything
> I am doing inherently wrong?
>
> Here is the command line I am using:
>
> ~/hadoop/bin/hadoop jar
> /home/hadoop/hadoop/contrib/streaming/hadoop-0.17.2.1-streaming.jar
> -inputformat org.apache.hadoop.mapred.SequenceFileAsTextInputFormat
> -mapper /home/hadoop/crawl_map -reducer NONE -jobconf
> mapred.output.compress=true -jobconf
> mapred.output.compression.codec=org.apache.hadoop.io.compress.LzoCodec
> -input pages -output crawl.lzo -jobconf mapred.reduce.tasks=0
>
> The input is in in form of URLs stored as a SequenceFile
>
> When running this without LZO compression, no such issue occurs.
>
> Is there any way for me to recover the corrupted data as to be able to
> process it by other
> hadoop jobs or offline?
>
> Thanks,
>
> --
> Alex Feinberg
> Platform Engineer, SocialMedia Networks