Hmm... not sure about that. IMHO, if the old format is detected, then a 4-byte EOS marker should be used. If the new format is detected, then a 8-byte EOS marker should be used.
Regards Antoine. Le 07/08/2019 à 16:16, Wes McKinney a écrit : > You make a good point. For backward compatibility reasons, bytes 5 > through 8 would need to be unspecified padding bytes, I think. Does > that sound right? > > On Wed, Aug 7, 2019 at 9:02 AM Antoine Pitrou <anto...@python.org> wrote: >> >> >> 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 >>>
