Hadoop: The Definitive Guide has a good section on this. Chapter 12: Hive: User Defined Functions. It has a diagram that shows how things are called and when. The example I'm looking at shows this sequence:
(first instance) init() iterate(1) iterate(2) iterate(3) terminatePartial() (second instance) init() iterate(4) iterate(2) terminatePartial() (then) init() merge(3) merge(4) terminate() The UDAF being described is a max integer function, hence the merge ending up with the highest integer from each instance. -Aurora On Mar 11, 2011, at 9:54 AM, Christopher, Pat wrote: > Ahh, perfect. The docs don't agree terribly well but the case study is > great. The context for when merge() gets called was not clear to me. > > Thanks guys! > > Pat > > -----Original Message----- > From: Steven Wong [mailto:sw...@netflix.com] > Sent: Thursday, March 10, 2011 6:24 PM > To: user@hive.apache.org > Cc: Christopher, Pat > Subject: RE: UDAF documentation > > Take a look at http://wiki.apache.org/hadoop/Hive/GenericUDAFCaseStudy, in > case you haven't found it already. > > > -----Original Message----- > From: Edward Capriolo [mailto:edlinuxg...@gmail.com] > Sent: Thursday, March 10, 2011 6:18 PM > To: user@hive.apache.org > Cc: Christopher, Pat > Subject: Re: UDAF documentation > > On Thu, Mar 10, 2011 at 8:27 PM, Christopher, Pat > <patrick.christop...@hp.com> wrote: >> Hi Guys, >> >> I'm writing a UDAF to run against hive 0.5 or hive 0.7. The documentation I >> can find says to implement UDAFEvaluator and ensure that you implement >> init() , aggregate() and evaluate(). However, all of the examples I can >> find implement init(), iterate(), merge(), terminatePartial() and >> terminate(). >> >> >> >> What's the difference and where I can find the documentation on how to write >> a UDAF? >> >> >> >> Thanks, >> >> Pat > > At time the documentation may lag behind the code. I would checkout > the hive source code for the version you are working with and base > your work on other already existing UDAF's that are similar. > > Edward >
