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Feb 11, 2024 420 likes •657 views

opencypher.org opencypher.org | opencypher@googlegroups.com opencypher.org opencypher.org | opencypher@googlegroups.com START john=node:Person(name="John") MATCH john-[:KNOWS]-friend-[:KNOWS]-foaf RETURN

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START john=node:Person(name="John") MATCH john-[:KNOWS]-friend-[:KNOWS]-foaf RETURN foaf

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START john=node:Person(name="John") MATCH (john)-[:KNOWS]-(friend)-[:KNOWS]-(foaf) WHERE NOT (john)-[:KNOWS]-(foaf) AND NOT (john)-[:RECOMMENDATION]->(foaf) CREATE (john)-[:RECOMMENDATION]->(foaf) RETURN foaf

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MATCH (john:Person{name:"John"}), (john)-[:KNOWS]-(friend)-[:KNOWS]-(foaf) WHERE NOT (john)-[:KNOWS]-(foaf) MERGE (john)-[:RECOMMENDATION]->(foaf)

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Query => AST => AST’ AST’ => Query Graph => Logical Plan L Plan => Instruction => CodeGen => JVM Class

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(query:String)-[:PARSED_TO]->(:AST {pos: $pos})

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SemanticState => SemanticState

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The AST is optimised and canonicalized Custom functional rewriting code

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Output: Logical Plans similar to relational query plans Expand/VarExpand are the main differences to normal relational algebra

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Similar to the System R - Dynamic Programming Quick Reminder, the Selinger Algorithm: 1. Enumerate all access paths for single relation 2. Consider all ways to join two relations 3. Consider all ways to join three relations, etc

[Access path selection in a relational database management system, Selinger et al]

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Neo4j Cost Planner 1. Enumerate all access paths for pattern nodes 2. Consider all ways to expand pattern relationships 3. Consider all ways to solve two pattern relationships, either by expand or join, etc for three, four patter relationships

[Iterative dynamic programming: a new class of query optimization algorithms, Kossman, Stocker]

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Pattern: (a)-[r1]->(b)<-[r2]-(c) |a| e-[r1]-> (b) e-[r2]-> (c) ⋈ |a| |c| e-[r1]-> (b) e(b)<-[r2]- Solutions:

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IDPSolver SingleComponentPlanner CardinalityCostModel

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  • accept(...)

L Plan => Instruction => CodeGen => JVM Class

[Efficiently Compiling Efficient Query Plans for Modern Hardware, Thomas Neumann]

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Cypher MATCH (n) WHERE n.x = 100 RETURN n Instruction

While(Variable("v1") -> ScanAllNodes()){ Selection( If("v1=100", AcceptVisitor( Map("n"-> NodeProjection(Variable("v1")))))) } )

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AllNodesScan Filter Project

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AllNodesScan Filter Project

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