On 13/05/2015 17:13, Chris Nauroth wrote:
It was important to complete this upgrade before Hadoop 2.x came out of beta. After that, we committed to a policy of backwards-compatibility within the 2.x release line. I can't find a statement about whether or not Protocol Buffers 2.6.1 is backwards-compatible with 2.5.0 (both at compile time and on the wire). Do you know the answer? If it's backwards-incompatible, then we wouldn't be able to do this upgrade within Hadoop 2.x, though we could consider it for 3.x (trunk).
I'm not sure about the wire format, what's the best way of checking for wire format issues?
http://upstream-tracker.org/versions/protobuf.html suggests there are are some source-level issues which will require investigation.
In general, we upgrade dependencies when a new release offers a compelling benefit, not solely to keep up with the latest. In the case of 2.5.0, there was a performance benefit. Looking at the release notes for 2.6.0 and 2.6.1, I don't see anything particularly compelling. (That's just my opinion though, and others might disagree.)
I think bundling or forking is the only practical option. I was looking to see if we could provide ProtocolBuffers as an installable option on our platform, if it's a version-compatibility nightmare as you say, that's going to be difficult as we really don't want to have to provide multiple versions.
BTW, if anyone is curious, it's possible to try a custom build right now linked against 2.6.1. You'd pass -Dprotobuf.version=2.6.1 and -Dprotoc.path=<path to protoc 2.6.1 binary> when you run the mvn command.
Once I have fixed all the other source portability issues I'll circle back around and take a look at this.
-- Alan Burlison --
