This may be coming a bit late, but I realize we could take the opportunity to *also* make the end-of-stream marker a 8-bytes marker (rather than 4-bytes). What do you think?
Regards Antoine. Le 06/08/2019 à 22:15, Wes McKinney a écrit : > hi all, > > As we've been discussing for the last 5 weeks or so [1], there is a > need to introduce 4 bytes of padding into the preamble of the > "encapsulated IPC message" format to ensure that the Flatbuffers > metadata payload begins on an 8-byte aligned memory offset. The > alternative to this would be for Arrow implementations where alignment > is important (e.g. C or C++) to copy the metadata (which is not always > small) into memory when it is unaligned. > > Micah has proposed to address this by adding a 4-byte "continuation" > value at the beginning of the payload having the value 0xFFFFFFFF. The > reason to do it this way is that old clients will see an invalid > length (what is currently the first 4 bytes of the message -- a 32-bit > little endian signed integer indicating the metadata length) rather > than potentially crashing on a valid length. > > This would be a backwards incompatible protocol change, so older Arrow > libraries would not be able to read these new messages. Maintaining > forward compatibility (reading data produced by older libraries) would > be possible as we can reason that a value other than the continuation > value was produced by an older library (and then validate the > Flatbuffer message of course). Arrow implementations could offer a > backward compatibility mode for the sake of old readers if they desire > (this may also assist with testing). > > The PR making these changes to the IPC documentation is here > > https://github.com/apache/arrow/pull/4951 > > Please vote to accept this change. This vote will be open for at least 72 > hours > > [ ] +1 Adopt the Arrow protocol change > [ ] +0 > [ ] -1 I disagree because... > > Here is my vote: +1 > > Thanks, > Wes > > [1]: > https://lists.apache.org/thread.html/8440be572c49b7b2ffb76b63e6d935ada9efd9c1c2021369b6d27786@%3Cdev.arrow.apache.org%3E >
