I think this kind of compatibility issue still could surface for HDFS, particularly for custom applications (i.e. something not executed via "hadoop jar" on a cluster node, where the client classes ought to be injected into the classpath automatically). Running DistCP between 2 clusters of different versions could result in a 2.4.0 client calling a 2.3.0 NameNode. Someone could potentially pick up the 2.4.0 WebHDFS client as a dependency and try to use it to make HTTP calls to a 2.3.0 HDFS cluster.
Chris Nauroth Hortonworks http://hortonworks.com/ On Wed, Mar 19, 2014 at 4:28 PM, Vinod Kumar Vavilapalli <vino...@apache.org > wrote: > It makes sense only for YARN today where we separated out the clients. > HDFS is still a monolithic jar so this compatibility issue is kind of > invalid there. > > +vinod > > On Mar 19, 2014, at 1:59 PM, Chris Nauroth <cnaur...@hortonworks.com> > wrote: > > > I'd like to discuss clarification of part of our compatibility policy. > > Here is a link to the compatibility documentation for release 2.3.0: > > > > > http://hadoop.apache.org/docs/r2.3.0/hadoop-project-dist/hadoop-common/Compatibility.html#Wire_compatibility > > > > For convenience, here are the specific lines in question: > > > > Client-Server compatibility is required to allow users to continue using > > the old clients even after upgrading the server (cluster) to a later > > version (or vice versa). For example, a Hadoop 2.1.0 client talking to a > > Hadoop 2.3.0 cluster. > > > > Client-Server compatibility is also required to allow upgrading > individual > > components without upgrading others. For example, upgrade HDFS from > version > > 2.1.0 to 2.2.0 without upgrading MapReduce. > > > > Server-Server compatibility is required to allow mixed versions within an > > active cluster so the cluster may be upgraded without downtime in a > rolling > > fashion. > > > > Notice that there is no specific mention of upgrading the client ahead of > > the server. (There is no clause for "upgraded client + old server".) > > Based on my experience, this is a valid use case when a user wants to > pick > > up a client-side bug fix ahead of the cluster administrator's upgrade > > schedule. > > > > Is it our policy to maintain client compatibility with old clusters > within > > the same major release? I think many of us have assumed that the answer > is > > yes and coded our new features accordingly, but it isn't made explicit in > > the documentation. Do we all agree that the answer is yes, or is it > > possibly up for debate depending on the change in question? In RFC 2119 > > lingo, is it a MUST or a SHOULD? Either way, I'd like to update the > policy > > text to make our decision clear. After we have consensus, I can > volunteer > > to file an issue and patch the text of the policy. > > > > This discussion started initially in MAPREDUCE-4052, which involved > > changing our scripting syntax for MapReduce YARN container submissions. > We > > settled the question there by gating the syntax change behind a > > configuration option. By default, it will continue using the existing > > syntax currently understood by the pre-2.4.0 NodeManager, thus preserving > > compatibility. We wanted to open the policy question for wider > discussion > > though. > > > > Thanks, everyone. > > > > Chris Nauroth > > Hortonworks > > http://hortonworks.com/ > > > > -- > > CONFIDENTIALITY NOTICE > > NOTICE: This message is intended for the use of the individual or entity > to > > which it is addressed and may contain information that is confidential, > > privileged and exempt from disclosure under applicable law. If the reader > > of this message is not the intended recipient, you are hereby notified > that > > any printing, copying, dissemination, distribution, disclosure or > > forwarding of this communication is strictly prohibited. If you have > > received this communication in error, please contact the sender > immediately > > and delete it from your system. Thank You. > > > -- > CONFIDENTIALITY NOTICE > NOTICE: This message is intended for the use of the individual or entity to > which it is addressed and may contain information that is confidential, > privileged and exempt from disclosure under applicable law. If the reader > of this message is not the intended recipient, you are hereby notified that > any printing, copying, dissemination, distribution, disclosure or > forwarding of this communication is strictly prohibited. If you have > received this communication in error, please contact the sender immediately > and delete it from your system. Thank You. > -- CONFIDENTIALITY NOTICE NOTICE: This message is intended for the use of the individual or entity to which it is addressed and may contain information that is confidential, privileged and exempt from disclosure under applicable law. If the reader of this message is not the intended recipient, you are hereby notified that any printing, copying, dissemination, distribution, disclosure or forwarding of this communication is strictly prohibited. If you have received this communication in error, please contact the sender immediately and delete it from your system. Thank You.
