Bzip2 is only splittable in newer versions of hadoop. On Jun 10, 2013 10:28 PM, "Alan Crosswell" <[email protected]> wrote:
> Ignore what I said and see > https://forums.aws.amazon.com/thread.jspa?threadID=51232 > > bzip2 was documented somewhere as being splittable but this appears to not > actually be implemented at least in AWS S3. > /a > > > On Mon, Jun 10, 2013 at 12:41 PM, Alan Crosswell <[email protected]> > wrote: > > > 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 > >> >> > > >> >> > >> > > >> > > >> > > >> > > > > >
