On Tue, Dec 5, 2017 at 1:33 PM, Chris Thunes <[email protected]> wrote:
> Thanks Feng. It seems like the GeneratedMessage / GeneratedMessageV3 split
> introduced between 3.0.0-beta-4 and the 3.0.0 final release caused the
> java/compatability_tests suite to start failing when run against 2.5.0 /
> 2.6.1 ("java/compatibility_tests/v2.5.0/test.sh 2.5.0" passes at git tag
> v3.0.0-beta-4 but fails at v3.0.0).
>
This is expected. Only 3.0.0-beta-4 is intended to be compatible with 2.5.0/
2.6.1. The final 3.0.0 release is not compatible with 2.5.0/2.6.1. 3.0.0
release is compatible with 3.0.0-beta-4 though. So a migration path could
be:
1. Move individual components to depend on 3.0.0-beta-4 instead of 2.5.0/
2.6.1. Since 3.0.0-beta-4 is compatible with 2.5.0/2.6.1 you don't need to
upgrade everything at once but can do it incrementally.
2. Once every component is on 3.0.0-beta-4, upgrade the dependency to 3.x.x.
This is how we do the migration inside google, but I guess it's hard to do
the same in the opensource world because you don't have control over your
dependencies.
> In 3.0.0 and newer, what is the role of the non-V3 variants of
> GeneratedMessage, SingleFieldBuilder, etc? Are these classes simply
> vestigial at this point or do they still provide some benefit to
> compatibility (even if not 100%).
>
They are still needed to be compatible with older beta releases like
3.0.0-beta-3 etc.
>
> Thanks again,
> Chris
>
> On Mon, Dec 4, 2017 at 8:24 PM, Feng Xiao <[email protected]> wrote:
>
>>
>>
>> On Mon, Dec 4, 2017 at 9:00 AM, Chris Thunes <[email protected]> wrote:
>>
>>>
>>> I'm looking at options for moving some applications that currently
>>> depend on protobuf-java 2.5.0 to a more recent version. This is made
>>> complicated by the fact that we have a mixure of internal and external
>>> dependencies (Hadoop & HBase) which depend on protobuf-java. My
>>> understanding is that this will require these dependencies to move to a 3.x
>>> release sychronously (i.e. regenerate using a 3.x protoc and update
>>> protobuf-java to a corresponding release).
>>>
>>> However, looking through release notes and protobuf source code it seems
>>> like some attempts have been made to address the source and binary
>>> compatibility issues between 2.5/2.6.1 and 3.x. Specifically,
>>>
>>> - The 3.0.0-beta-4 release notes
>>> <https://github.com/google/protobuf/blob/v3.0.0-beta-4/CHANGES.txt>
>>> mention runtime updates "to be compatible with 2.5.0/2.6.1 generated
>>> protos".
>>> - A number of classes have "V3" variants where the non-V3 variants
>>> appear to exist solely in an attempt to maintain binary compatibility
>>> with
>>> pre-3.x generated code.
>>>
>>> Running the compatibility tests in java/compatibility_tests/v2.5.0 it
>>> appears that source and binary incompatibilities still exist.
>>>
>>>
>>> I'm curious if anyone can shed some light on this effort and its status
>>> or provide suggestions for migrating to a recent protobuf release under
>>> these circumstances.
>>>
>> Protobuf 2.5.0/2.6.1 should be compatible with 3.0.0-beta-4 if you only
>> uses protobuf public APIs. That's unfortunately not the case with Hadoop &
>> HBase though. They introduced a class into com.google.protobuf package
>> with the sole purpose to access protobuf package private classes
>> <https://github.com/apache/hbase/blob/master/hbase-protocol/src/main/java/com/google/protobuf/HBaseZeroCopyByteString.java>.
>> As
>> such there is no way you can upgrade to protobuf 3.x if the version of
>> Hadoop & HBase you use still depends on protobuf 2.5/2.6 private symbols.
>>
>>
>>> Thanks,
>>>
>>> Chris
>>>
>>>
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>>
>>
>
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