Home | About | Sematext search-lucene.com search-hadoop.com
 Search Hadoop and all its subprojects:

Switch to Threaded View
Pig, mail # user - prep for cassandra storage from pig


Copy link to this message
-
Re: prep for cassandra storage from pig
William Oberman 2011-06-15, 19:08
My problem is the column names are dynamic (a date), and pygmalion seems to
want the column names to be fixed at "compile time" (the script).

On Wed, Jun 15, 2011 at 3:04 PM, Jeremy Hanna <[EMAIL PROTECTED]>wrote:

> Hi Will,
>
> That's partly why I like to use FromCassandraBag and ToCassandraBag from
> pygmalion - it does the work for you to get it back into a form that
> cassandra understands.
>
> Others may know better how to massage the data into that form using just
> pig, but if all else fails, you could write a udf to do that.
>
> Jeremy
>
> On Jun 15, 2011, at 1:17 PM, William Oberman wrote:
>
> > I think I'm stuck on typing issues trying to store data in cassandra.  To
> verify, cassandra wants (key, {tuples})
> >
> > My pig script is fairly brief:
> > raw = LOAD 'cassandra://test_in/test_cf' USING CassandraStorage() AS
> (key:chararray, columns:bag {column:tuple (name, value)});
> > --colums == timeUUID -> JSON
> > rows = FOREACH raw GENERATE key, FLATTEN(columns);
> > alias_target_day = FOREACH rows {
> >     --I wrote a specialized parser that does exactly what I need
> >     observation_map = com.civicscience.pig.ParseObservation($2);
> >     GENERATE $0 as alias, observation_map#'_fqt' as target,
> observation_map#'_day' as day;
> > };
> > grouping = GROUP alias_target_day BY ((chararray)target,(chararray)day);
> > X = FOREACH grouping GENERATE group.$0 as target, TOTUPLE(group.$1,
> COUNT($1)) as day_count;
> >
> > This gets me:
> > (targetA, (day1, count))
> > (targetA, (day2, count))
> > (targetB, (day1, count))
> > ....
> >
> > But, cassandra wants the 2nd item to be a bag.  So, I tried:
> > X = FOREACH grouping GENERATE group.$0 as target, TOBAG(TOTUPLE(group.$1,
> COUNT($1))) as day_count;
> >
> > But this results in:
> > (targetA, {((day1, count))})
> > (targetA, {((day2, count))})
> > (targetB, {((day1, count))})
> > It's hard to see, but the 2nd item now has a nested tuple as the first
> value, which is still bad.
> >
> > How to I get (key, {tuple})???  I wasn't sure where to post this (pig or
> cassandra), so I'm posting to the pig list too.
> >
> > will
>
>
--
Will Oberman
Civic Science, Inc.
3030 Penn Avenue., First Floor
Pittsburgh, PA 15201
(M) 412-480-7835
(E) [EMAIL PROTECTED]