some question about new go plan

[nevermore3]

Is your feature request related to a problem? Please describe.

The go statement is divided into two operators, expand operator and expandAll operator. expand is responsible for expansion and does not take attributes. expandAll is responsible for expansion and take attributes that user need.

go 3 steps from 'Tim Duncan' over like yield like._dst as id limit [2, 2, 2]

previous plan

When there is a limit in each step, the previous plan is that the limit operator in each step is pushed down to the storage layer, and then do limit in graph layer again

new plan

In expand & expandAll, use the adjacency list to save the already visited vertex and corresponding edges. When the visited vertex are visited again, the data is fetched from the adjacency list instead of RPC.

When there is a limit in each step, In order to ensure the integrity of the data in the adjacency list, limit will not be push down to storage, so there will be a loss in performance in this scenario

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