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: '[email protected]'}) 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 cypher MATCH (u:User) WHERE u.age > $age RETURN u

  2. Create Indexes cypher CREATE INDEX ON :User(email)

  3. Limit Results cypher MATCH (u:User) RETURN u LIMIT 100

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

Next Steps#

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