Joe, You know you mentioned HBase, but have you thought about it?
This is actually a simple thing to do in HBase because in your map/reduce you hash your key and then check to see if HBase already has your key. (You make your hbase connection in setup() so you don't constantly open/close connections....[Sorry, its a common mistake...]) Actually reading from HDFS and writing to HBase is pretty simple in 20.x stuff. Also I tend to like SHA1 encryption for the keys. There's enough documentation to show that the SHA1 hash is almost guaranteeing a unique hash. There's some variations on this, but its pretty fast. Of course I'm assuming that you don't want to just dedup against the current job, but may want to dedupe againt prior jobs as well? Even if its for the same job and the table is temporary, it may be faster... -Mike > Date: Thu, 25 Mar 2010 14:35:23 -0400 > Subject: Re: DeDuplication Techniques > From: crypt...@gmail.com > To: common-user@hadoop.apache.org > > The thing is I have to check historic data (meaning data I have > already aggregated against) so I basically need to hold and read from > a file of hashes. > > So within the current data set yes this would work but I then have to > open a file, loop through the value, see it is not there. > > If it is there then throw it out, if not there add it to the end. > > To me this opening a file checking for dups is a map/reduce task in itself. > > What I was thinking is having my mapper take the data I wasn to > validate as unique. I then loop through the files filters. each data > point has a key that then allows me to get the file that has it's > data. e.g. a part of the data partions the hash of the data so each > file holds. So my map job takes the data and breaks it into the > key/value pair (the key allows me to look up my filter file). > > When it gets to the reducer... the key is the file I open up, I then > open the file... loop through it... if it is there throw the data > away. if it is not there then add the hash of my data to the filter > file and then output (as the reduce output) the value of the unique. > > This output of the unique is then the data I aggregate on which also > updated my historic filter so the next job (5 minutes later) see it, > etc. > > On Thu, Mar 25, 2010 at 2:25 PM, Mark Kerzner <markkerz...@gmail.com> wrote: > > Joe, > > > > what about this approach: > > > > using hashmap values as your keys in MR maps. Since they are sorted by keys, > > in reducer you will get all duplicates together, so that you can loop > > through them. As the simplest solution, you just take the first one. > > > > Sincerely, > > Mark > > > > On Thu, Mar 25, 2010 at 1:09 PM, Joseph Stein <crypt...@gmail.com> wrote: > > > >> I have been researching ways to handle de-dupping data while running a > >> map/reduce program (so as to not re-calculate/re-aggregate data that > >> we have seen before[possibly months before]). > >> > >> The data sets we have are littered with repeats of data from mobile > >> devices which continue to come in over time (so we may see duplicates > >> of data re-posted months after it originally posted...) > >> > >> I have 2 ways so far I can go about it (one way I do in production > >> without Hadoop) and interested to see if others have faced/solved this > >> in Hadoop/HDFS and what their experience might be. > >> > >> 1) handle my own hash filter (where I continually store and look up a > >> hash (MD5, bloom, whatever) of the data I am aggregating on as > >> existing already). We do this now without Hadoop perhaps a variant > >> can be ported into HDFS as map task, reducing the results to files and > >> restoring the hash table (maybe in Hive or something, dunno yet) > >> 2) push the data into Cassandra (our NoSQL solution of choice) and let > >> that hash/map system do it for us. As I get more into Hadoop looking > >> at HBas is tempting but then just one more thing to learn. > >> > >> I would really like to not have to reinvent a wheel here and even > >> contribute if something is going on as it is a use case in our work > >> effort. > >> > >> Thanx in advance =8^) Apologize I posted this on common dev yesterday > >> by accident (so this is not a repost spam but appropriate for this > >> list) > >> > >> Cheers. > >> > >> /* > >> Joe Stein > >> http://www.linkedin.com/in/charmalloc > >> */ > >> > > > > > > -- > /* > Joe Stein > http://www.linkedin.com/in/charmalloc > */ _________________________________________________________________ Hotmail is redefining busy with tools for the New Busy. Get more from your inbox. http://www.windowslive.com/campaign/thenewbusy?ocid=PID27925::T:WLMTAGL:ON:WL:en-US:WM_HMP:032010_2
