A ValTransaction that wraps a BTreeMap. It supports basic BTreeMap operations like get,
get_mut, insert and remove. Incremental modification of insert, remove and get_mut
are stored in staging. On commit, it will apply the changes stored in staging to the in
memory btree map. When serve get and get_mut, it merges the value stored in staging and
tree_ref.
A mutable guard to the value of the corresponding key of a BTreeMapTransaction.
The staging value is initialized in a lazy manner, that is, the staging value is only cloned
from the original value only when it’s being mutably deref.
Transaction wrapper for a variable.
In first deref_mut call, a copy of the original value will be assigned to new_value
and all subsequent modifications will be applied to the new_value.
When commit is called, the change to new_value will be applied to the orig_value_ref
When abort is called, the VarTransaction is dropped and the local memory value is
untouched.
The newly added no-shuffle actor dispatcher from upstream fragment to downstream fragment
upstream fragment_id -> downstream fragment_id -> upstream actor_id -> downstream actor_id