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Query Engine

QilbeeDB's query engine implements OpenCypher with cost-based optimization and vectorized execution.

Architecture

Cypher Query → Parser → Planner → Optimizer → Executor

Query Processing

1. Parsing

Convert Cypher text into Abstract Syntax Tree (AST):

MATCH (u:User {name: 'Alice'})-[:KNOWS]->(f)
RETURN f.name

2. Planning

Generate optimized execution plan with cost-based optimization:

Return[f.name]
  ↑
Expand[(u)-[:KNOWS]->(f)]
  ↑
IndexSeek[User.name = 'Alice']

3. Execution

Execute plan using physical operators:

  • NodeScan: Scan all nodes with label
  • IndexSeek: Use index for exact match
  • Filter: Apply WHERE predicate
  • Expand: Traverse relationships
  • Project: Select output columns

Optimization Techniques

Index Selection

Automatically uses indexes when available:

-- Create index
CREATE INDEX ON :User(email)

-- Fast lookup
MATCH (u:User {email: 'alice@example.com'}) RETURN u

Predicate Pushdown

Move filters close to data source to reduce scanned data.

Cardinality Estimation

Estimate result sizes for better planning.

Join Reordering

Choose optimal join order based on estimated costs.

Performance Tips

  1. Use Parameters 

    MATCH (u:User) WHERE u.age > $age RETURN u

  2. Create Indexes 

    CREATE INDEX ON :User(email)

  3. Limit Results 

    MATCH (u:User) RETURN u LIMIT 100

  4. Use EXPLAIN 

    EXPLAIN MATCH (u:User)-[:KNOWS*2..3]->(f) RETURN f

Next Steps