Avoid checking for existing tasks while pruning

When the distributor runs, it now stores a snapshot of pending
pushes and then removes from this snapshot all the RefUpdates
which were found while adding pending persisted tasks. The
remaining pushes in the snapshot can now be pruned without
needing to do an existence check on them since they were no
longer stored persistently (and thus no longer needed to be
executed). This effectively makes pruning I/O less, thereby
reducing the load put by distributor on disk I/O.

Change-Id: I0916a57b302fd7d207fd31ec26df65d262a76124
2 files changed
tree: c1f26226b71d5a1112b810530ed845f2ea506d7d
  1. .gitignore
  2. .mailmap
  3. .settings/
  4. BUILD
  5. LICENSE
  6. src/