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https://issues.apache.org/jira/browse/HBASE-16567?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15470479#comment-15470479
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stack commented on HBASE-16567:
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HBASE-15638 is where I'm trying to find the classloader magic. tl;dr I've not
found it yet. [~Apache9]
> Upgrade to protobuf3
> --------------------
>
> Key: HBASE-16567
> URL: https://issues.apache.org/jira/browse/HBASE-16567
> Project: HBase
> Issue Type: Task
> Components: Protobufs
> Affects Versions: 2.0.0
> Reporter: stack
> Assignee: stack
> Priority: Critical
> Attachments: HBASE-16567.master.001.patch
>
>
> Move master branch on to protobuf3. See
> https://github.com/google/protobuf/releases We'd do it because pb3 saves some
> on byte copies can work with offheap buffers -- needed for the off-heap write
> path project -- though read-time is still a TODO (this means pb3 is not
> enough; we'll have to patch it -- or patch pb2.5).
> HBASE-15638 has us first shading protobufs before upgrading. Let us list here
> issues just going to pb3 without shading if only for completeness sake; i.e.
> do we have to shade?
> * pb3 is by default wire compatible with pb2.
> * protoc3 run against our .protos works fine except pb3 breaks our
> HBaseZeroCopyLiteralByteString hack so this has to be removed (possibly
> recast using new pb3 types)
> * Starting up a cluster that is all pb3 seems to work fine.
> * A pb2 branch-1 can read and write against the pb3 master cluster.
> What will break if we just upgrade to pb3?
> * We should be able to write HDFS messages on our AsyncWAL using pb3; the
> pb2 HDFS should be able to read them (not tested). Or maybe not. See policy
> here: https://github.com/google/protobuf/issues/1852 which seems to indicate
> pb3s will not be able to write compatible pb2 Messages. TODO.
> * Core Coprocessor Endpoints such as AccessControl seem to just work (their
> protos will have been protoc3'd). I did simple test with a server from master
> branch up on pb3 and then going against it with a branch-1 client on pb2. I
> was able to add grants.
> * For non-core CPEPs where the protos are pb2 still, it might just work. To
> test. It would not be the end-of-the-world if they did not.
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