[Plasma] plasma pushes notifications to all subscribers when a new client subscribes #18902
Description
When a new client subscribes to plasma store, plasma would push notifications about existing objects to the new subscriber - while the current code pushes notifications to ALL subscribers in this case which is unnecessary.
Reporter: Zhijun Fu / @zhijunfu
PRs and other links:
Note: This issue was originally created as ARROW-2556. Please see the migration documentation for further details.