1. if i enable batch mode, is it safe to assume that a batch will be assigned to a single hython?
   for example, if i use batch with say a size of 64, TOPs will assign 1 batch to 1 hython, then process 64 workitems in that hython?
   so if i have 256 workitems, HDA processor can create 4 batches?
   
2. will a batch be processed sequentially (by index)? or is it random?
   
3. if a workitem inside a batch get's an error, will it fail the batch associated with it?
   

Yea, a batch will process all of its work items in one process. Rather than cooking each work item individually, the batch itself is scheduled as a single logical job. For both ROP Fetch and HDA Processor batches are processed sequentially, however that's not a strict requirement. For example, if you're writing a custom work item job script that supports batching (or a Python Processor's onCookTask hook) you can process the items in the batch in whatever order you want.

The ROP Fetch node cooks batches by calling rop.render(..) over the whole frame range, so if an error occurs on a frame the entire operation ends early. Likewise for HDA Processor -- the work items are cooked in a loop, and a failure will cause the process to exit immediately.

thank you for the answers and confirmation ^_^