Remove vertex ID recycle function #2558
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why: It is not safe in general to recycle vertex IDs while the `RocksDb` cache has `VertexID` rather than `RootedVertexID` where the former type seems preferable. In some fringe cases one might remove a vertex with key `(root1,vid)` and insert another vertex with key `(root2,vid)` while re-using the vertex ID `vid`. Without knowledge of `root1` and `root2`, the LRU cache will return the same vertex for `(root2,vid)` also for `(root1,vid)`.
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why:
It is not safe in general to recycle vertex IDs while the
RocksDbcache has
VertexIDrather thanRootedVertexIDwhere the formertype seems preferable.
In some fringe cases one might remove a vertex with key
(root1,vid)and insert another vertex with key
(root2,vid)while re-using thevertex ID
vid. Without knowledge ofroot1androot2, the LRUcache will return the same vertex for
(root2,vid)also for(root1,vid).