waynexia commented on PR #6336:
URL: https://github.com/apache/arrow-rs/pull/6336#issuecomment-2378646907

   > As I understand it this mechanism would require making every codepath that 
allocates arrays be generic on an Allocator and take an Allocator as a 
parameter.
   
   IMO this is not that horrible in two aspects:
   - I suspect the type param on struct would only reside on `MutableBuffer` 
for a long time, maybe until the `Allocator` gets stable. From `Buffer` and 
above the type param is erased (see #6455). Like how we interact with `Vec` 
which may or may not belong to a customized allocator: nothing is wrong if we 
just ignore it, only a "feature" is missing.
   - We can gain great progress after the major mechanisms of constructing an 
array like through `Vec` or `MutableBuffer` are handled. 
   
   There is still much work to do to adapt those methods. But they are not that 
tightly coupled together like `MutableBuffer` and `Buffer`.
   
   > Additionally the proposed use-cases appear to largely center around memory 
tracking, as opposed to altering the behaviour of the system allocator. As such 
we could potentially just store a std::sync::Weak<AtomicUsize> in thread local 
storage, with allocations decrementing / incrementing this as appropriate.
   
   If we don't need per-object tracking, simply replace the global allocator as 
@alamb mentioned before should be okay. And this is already viable in the 
current version as we don't need to do any change in the arrow side.
   
   And considering the arrow is a large group of libs, we don't have to take 
this `allocator` feature as "can or can't" for the entire project. It is 
acceptable from my side that this feature is only available in a few low-level 
APIs like `arrow-buffer` and isn't in others like `arrow-compute` in a specific 
period.


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