Graph RAG uses explicit relationships to retrieve evidence for a generated answer. Vector RAG retrieves passages by similarity to a query. A graph is useful when the question depends on connections that are difficult to recover from one passage, but it brings extraction, identity, and maintenance work that a simpler retrieval system may not need.

Choose between them by the questions you must answer. A product FAQ and a dependency investigation can use the same documents while requiring very different retrieval behavior.

Distinguish the question types

Question	First approach to test	Reason
“How do I configure retries?”	Lexical or vector passage retrieval	A relevant section may contain the full answer
“Which services depend on this database?”	A structured dependency graph or database query	The answer requires explicit edges
“What themes recur across these reports?”	Corpus summaries or a graph-assisted global method	No single nearest passage necessarily represents the corpus
“What did this customer prefer last quarter?”	Time-aware records and retrieval	Historical validity matters more than choosing a graph label

You do not need a graph merely because the answer uses two documents. A well-designed retrieval system may return both passages. Conversely, storing edges does not guarantee that an extracted relationship is correct.

What counts as Graph RAG?

The term covers several designs. Some retrieve neighboring entities and their source passages. Others build communities or summaries to answer broader corpus questions. Microsoft's GraphRAG project is a particular implementation of graph-assisted retrieval and summarization, not a name for every system that stores relationships.

Be precise when comparing experiments. A vector baseline answering local fact questions and a graph system answering corpus-wide themes are not solving an identical task. Compare matched questions, source versions, generation settings, and costs.

Follow a relationship with its evidence

Imagine a fictional service map:

checkout-api -> depends_on -> pricing-service
pricing-service -> depends_on -> catalog-db
support-api -> depends_on -> customer-db

“Could a catalog-db outage affect checkout?” has a two-edge candidate path. To turn that into a reliable answer, the system needs evidence that those dependencies are current, that the direction is correct, and that the user may see the service map. It should also distinguish dependency from guaranteed failure: caching or fallback behavior may change the impact.

Attach a source revision and observation time to each edge. If one relationship was inferred from a stale design document, disclose that limitation or verify it against current configuration. A graph path can make reasoning inspectable while still being wrong at its inputs.

Budget for entity resolution and updates

“Catalog,” “catalog service,” and “catalog-db” might refer to different components. Merging them because their names look similar can create false paths. Failing to merge genuine aliases can disconnect relevant evidence.

Start with stable IDs from an authoritative system where available. Use model extraction to propose relationships when needed, but validate the relationship types and retain provenance. A generic “related to” edge often adds less value than a precise relation the query can actually use.

Updates are equally important. When a service migrates databases, the old dependency should stop answering present-tense questions. Preserve it only if historical questions are part of the product. The temporal-memory guide covers effective time and late-arriving evidence.

Combine retrieval methods at clear boundaries

A practical design can use lexical or vector search to identify the likely entity, traverse a bounded set of relationships, and fetch the original supporting passages. Limit the expansion by relation type, access scope, depth, and relevance.

Unbounded graph expansion can produce a large neighborhood with little useful evidence. The answer model then faces the same context-selection problem as an oversized vector result set. Record which paths contributed to the answer, rather than dumping every connected node into the prompt.

For the distinction between lexical/vector fusion and graph traversal, see hybrid search.

Evaluate the graph's incremental value

Build a fixture with direct lookups, explicit relationship questions, two-step paths, missing edges, conflicting sources, and changed relationships. Compare a passage-retrieval baseline with the graph-assisted path.

For each answer, inspect whether the required evidence was present, whether the cited path is valid, and whether the conclusion goes beyond what the path proves. Also measure ingestion work, extraction corrections, graph-query time, and context size.

A useful release criterion is not “we have a knowledge graph.” It is “the dependency questions that previously failed now receive supported answers, without worsening simpler questions or exposing inaccessible relationships.” Weigh the improvement against graph maintenance costs and the impact of the remaining failures.

Where does agent memory fit?

An agent memory graph may represent relationships between remembered facts and their updates. A domain knowledge graph may represent suppliers, services, accounts, or contracts. They can coexist, but they are not interchangeable schemas.

Supermemory documents relationships such as updates and extensions in its memory graph. That does not imply an arbitrary domain graph or a Neo4j-style query interface. Verify the operations you need before selecting it for a graph-specific workload.

Start with ten questions your existing retrieval fails. If the missing piece is a stable relationship path, prototype the smallest graph that can supply it. If the problem is poor chunking, stale documents, or missing exact-term retrieval, fix that first.

Build the first two-hop query with the small knowledge-graph tutorial, then test it against your failed questions.

If your use case is relationships between remembered facts, try Supermemory’s memory graph with the documented operations above. Use a changed decision as the first case and inspect what gets retrieved; keep domain-graph requirements in a separate evaluation.

Graph RAG vs Vector RAG: When Relationships Matter