General questions about Arrow & Plasma

[Matthias Vallentin]

Two question about Plasma; my use case is sharing Arrow data between a 
C++ and Python application (eventually also R). 

1. What's the typical memory allocation procedure when using Plasma and 
  Arrow? Do I first construct a builder, populate it, finish it, and 
  *then* copy it into mmaped buffer? Or do I obtain mmaped buffer from 
  Plasma first, in which the builder operates incrementally until it's 
  full? If I understand it correctly, a Plasma buffer has a fixed size, 
  so I wonder how you accommodate the fact that the Arrow builder 
  constructs a record batches incrementally, while at the same time 
  avoiding extra copying of large memory chunks after finishing the 
  builder.

1. Do I need Plasma to exchange the mmapped buffers between the two 
  apps? Or could I mmap my Arrow data manually and tell pyarrow through 
  a different mechanism to obtain the shared buffer? 

   Matthias