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Pig, mail # user - problems with .gz


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Re: problems with .gz
Alan Crosswell 2013-06-10, 16:41
Suggest that if you have a choice, you use bzip2 compression instead of
gzip as bzip2 is block-based and Pig can split reading a large bzipped file
across multiple mappers while gzip can't be split that way.
On Mon, Jun 10, 2013 at 12:06 PM, William Oberman
<[EMAIL PROTECTED]>wrote:

> I still don't fully understand (and am still debugging), but I have a
> "problem file" and a theory.
>
> The file has a "corrupt line" that is a huge block of null characters
> followed by a "\n" (other lines are json followed by "\n").  I'm thinking
> that's a problem with my cassandra -> s3 process, but is out of scope for
> this thread....  I wrote scripts to examine the file directly, and if I
> stop counting at the weird line, I get the "gz" count.   If I count all
> lines (e.g. don't fail at the corrupt line) I get the "uncompressed" count.
>
> I don't know how to debug hadoop/pig quite as well, though I'm trying now.
>  But, my working theory is that some combination of pig/hadoop aborts
> processing the gz stream on a null character, but keeps chugging on a
> non-gz stream.  Does that sound familiar?
>
> will
>
>
> On Sat, Jun 8, 2013 at 8:00 AM, William Oberman <[EMAIL PROTECTED]
> >wrote:
>
> > They are all *.gz, I confirmed that first :-)
> >
> >
> > On Saturday, June 8, 2013, Niels Basjes wrote:
> >
> >> What are the exact filenames you used?
> >> The decompression of input files is based on the filename extention.
> >>
> >> Niels
> >> On Jun 7, 2013 11:11 PM, "William Oberman" <[EMAIL PROTECTED]>
> >> wrote:
> >>
> >> > I'm using pig 0.11.2.
> >> >
> >> > I had been processing ASCII files of json with schema: (key:chararray,
> >> > columns:bag {column:tuple (timeUUID:chararray, value:chararray,
> >> > timestamp:long)})
> >> > For what it's worth, this is cassandra data, at a fairly low level.
> >> >
> >> > But, this was getting big, so I compressed it all with gzip (my "ETL"
> >> > process is already chunking the data into 1GB parts, making the .gz
> >> files
> >> > ~100MB).
> >> >
> >> > As a sanity check, I decided to do a quick check of pre/post, and the
> >> > numbers aren't matching.  Then I've done a lot of messing around
> trying
> >> to
> >> > figure out why and I'm getting more and more puzzled.
> >> >
> >> > My "quick check" was to get an overall count.  It looked like
> (assuming
> >> A
> >> > is a LOAD given the schema above):
> >> > -------
> >> > allGrp = GROUP A ALL;
> >> > aCount = FOREACH allGrp GENERATE group, COUNT(A);
> >> > DUMP aCount;
> >> > -------
> >> >
> >> > Basically the original data returned a number GREATER than the
> >> compressed
> >> > data number (not by a lot, but still...).
> >> >
> >> > Then I uncompressed all of the compressed files, and did a size check
> of
> >> > original vs. uncompressed.  They were the same.  Then I "quick
> checked"
> >> the
> >> > uncompressed, and the count of that was == original!  So, the way in
> >> which
> >> > pig processes the gzip'ed data is actually somehow different.
> >> >
> >> > Then I tried to see if there are nulls floating around, so I loaded
> >> "orig"
> >> > and "comp" and tried to catch the "missing keys" with outer joins:
> >> > -----------
> >> > joined = JOIN orig by key LEFT OUTER, comp BY key;
> >> > filtered = FILTER joined BY (comp::key is null);
> >> > -----------
> >> > And filtered was empty!  I then tried the reverse (which makes no
> sense
> >> I
> >> > know, as this was the smaller set), and filtered is still empty!
> >> >
> >> > All of these loads are through a custom UDF that extends LoadFunc.
>  But,
> >> > there isn't much to that UDF (and it's been in use for many months
> now).
> >> >  Basically, the "raw" data is JSON (from cassandra's sstable2json
> >> program).
> >> >  And I parse the json and turn it into the pig structure of the schema
> >> > noted above.
> >> >
> >> > Does anything make sense here?
> >> >
> >> > Thanks!
> >> >
> >> > will
> >> >
> >>
> >
> >
> >
>