Bertrand: Your questions are quite common ones. Let me try clarifying a few. Andy or Gary should be able to give better answers.
For #1, there is no support for coprocessor if your code is not compiled and built in a jar. Need to get bit more familiar with Cascading :-) For #2, can you give us some scenarios when parameters should be passed to coprocessor at runtime ? For #3, can you clarify the type of multiple blocks involved ? As you know, HBase organizes data into regions. For #5, it is up to you how to partition work between coprocessor (executed on region servers) and your client code. Cheers On Tue, Jul 24, 2012 at 7:59 AM, Bertrand Dechoux <[email protected]>wrote: > Hello, > > I am learning about coprocessors and would like to know more about how to > choose between coprocessors and MapReduce. > > First, I thought coprocessors needed a restart but it seems a shell can be > used to add/remove them without requiring a restart. However, at the moment > the coprocessors are defined within jar and can not be dynamically created. > Could you confirm that? (I am thinking about the Cascading way of creating > the implementation which will then be serialized, send and executed.) > > Second, I didn't see any way to give parameters to coprocessors. Is that > really the case? If not, how would the parameters be handled? > > Third, I assume coprocessors are using the processus/thread of the region > server. Does that means that, if multiple blocks need to be processed, > MaReduce should be more efficient? Are there other ways to know whether > coprocessors or MapReduce should be chosen? > > Fourth, I know this is a really broad question but how would you compare > coprocessors to YARN? I have yet to know more about both subjects but I > feel that the concepts are not totally unrelated. > > Lastly, this is an implementation detail but how the client side waits for > the results? Is it possible to perform early aggregation or does the client > need to receive all the information before doing anything else? > > Regards > > Bertrand > > > Ps : My two sources for that subject are for HBase 0.92 : > * https://blogs.apache.org/hbase/entry/coprocessor_introduction > * HBase The Definitive Guide. >
