Package io.trino.sql.planner.iterative

Class Memo

  • public class Memo
extends Object
    Stores a plan in a form that's efficient to mutate locally (i.e. without having to do full ancestor tree rewrites due to plan nodes being immutable).

    Each node in a plan is placed in a group, and it's children are replaced with symbolic references to the corresponding groups.

    For example, a plan like: 

        A -> B -> C -> D
           \> E -> F
    would be stored as: 
     root: G0

 G0 : { A -> G1 }
 G1 : { B -> [G2, G3] }
 G2 : { C -> G4 }
 G3 : { E -> G5 }
 G4 : { D }
 G5 : { F }
    Groups are reference-counted, and groups that become unreachable from the root due to mutations in a subtree get garbage-collected.