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HBase, mail # dev - Does compatibility between versions also mean binary compatibility?


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Re: Does compatibility between versions also mean binary compatibility?
Andrew Purtell 2013-04-05, 00:53
Thanks for taking the time for the thoughtful feedback James.

> - between 0.94.3 and 0.94.4, new methods were introduced on
RegionScanner. Often coprocessors will have their own implementation of
these so that they can aggregate in the postScannerOpen. Though this broke
binary compat, it improved scan performance as well. Where does the binary
compatible line stop?
> - between 0.94.3 and 0.94.4, the class loading changed for coprocessors.
If a coprocessor was on the classpath, it didn't matter what the jar path
was, it would load. In 0.94.4, that was no longer the case - if the jar
path was invalid, the coprocessor would no longer load. Though this broke
compatibility, it was a good cleanup for the class loading logic. Call it a
bug fix or a change in behavior, but either way it was an incompatible
change. Is a change in behavior that causes incompatibilities still meet
the binary compatible criteria?

As "owner" of this space, I will claim that no binary compatibility nor
even interface compatibility should be expected at this time even among
point releases. This is for two reasons, the first being most important:

    1) The Coprocessor API caters to only a few users currently, so feels
the pull of the gravity of these major (new) users, e.g. security, Francis
Liu's work, Phoenix. We can expect this to lessen naturally over time as --
exactly here -- users like Phoenix become satisfied with the status quo and
begin to push back. Your input going forward will be valuable.

    2) Coprocessors are an extension surface for internals

On Thu, Apr 4, 2013 at 4:29 PM, James Taylor <[EMAIL PROTECTED]> wrote:

> The binary compat is a slippery slope. It'd be a bummer if we couldn't
> take advantage of all the innovation you guys are doing. At the same time,
> it's tough to require the Phoenix user community, for example, to upgrade
> their HBase servers to be able to move to the latest version of Phoenix. I
> don't know what the right answer is, but here are a couple of concrete
> cases:
> - between 0.94.3 and 0.94.4, new methods were introduced on RegionScanner.
> Often coprocessors will have their own implementation of these so that they
> can aggregate in the postScannerOpen. Though this broke binary compat, it
> improved scan performance as well. Where does the binary compatible line
> stop?
> - between 0.94.3 and 0.94.4, the class loading changed for coprocessors.
> If a coprocessor was on the classpath, it didn't matter what the jar path
> was, it would load. In 0.94.4, that was no longer the case - if the jar
> path was invalid, the coprocessor would no longer load. Though this broke
> compatibility, it was a good cleanup for the class loading logic. Call it a
> bug fix or a change in behavior, but either way it was an incompatible
> change. Is a change in behavior that causes incompatibilities still meet
> the binary compatible criteria?
> - between 0.94.4 and 0.94.5, the essential column family feature was
> introduced. This is an example of one that is binary compatible. We're able
> to take advantage of the feature and maintain binary compatibility with
> 0.94.4 (in which case the feature simple wouldn't be available).
>
> Maybe if we just explicitly identified compatibility issues, that would be
> a good start? We'd likely need a way to find them, though.
>
>     James
>
> On 04/04/2013 03:59 PM, lars hofhansl wrote:
>
>> I agree we need both, but I'm afraid that ship has sailed.
>> It's not something we paid a lot of attention to especially being
>> forward-binary-compatible. I would guess that there will be many more of
>> these issues.
>>
>> Also, we have to qualify this statement somewhere. If you extend
>> HRegionServer you cannot expect compatibility between releases. Of course
>> that is silly, but it serves the point I am making.
>>
>> For client visible classes (such as in this case) we should make it work,
>> we identifies issues with Filters and Coprocessors in the past and kept
>> them binary compatible on a best effort basis.
Best regards,

   - Andy

Problems worthy of attack prove their worth by hitting back. - Piet Hein
(via Tom White)