Memory Architectures for AI Agents

When an agent hallucinates, the first instinct is to blame the model. Nine times out of ten that is the wrong diagnosis — the model is fine, the retrieval layer is broken. This decision guide maps three long-term memory architectures to the shape of your data: Vector RAG for unstructured text (Pinecone, Qdrant, ChromaDB, pgvector), Knowledge Graphs for relationship reasoning (Neo4j, LightRAG, GraphRAG), and Tabular/SQL for deterministic record lookup (PostgreSQL, SQLite, text-to-SQL). The full guide includes the 4-tier memory model, an animated decision flowchart with five sharpening questions, a 10-row head-to-head comparison, in-depth detail pages per architecture with strengths and failure modes, and the hybrid Memory Router pattern that production agents actually run.