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Database / Qdrant Vector DB Interview questions

What is the difference between Qdrant and Weaviate?

Both are open-source vector databases with self-hosted and managed cloud options, but they differ in core data modeling philosophy and some architectural emphases.

QdrantWeaviate
Rust core; collections of points with flexible JSON payloads.Go core; schema-driven classes with defined properties.
Payload schema is flexible; fields are typically indexed opt-in.Encourages more explicit upfront schema definition per class.
Built-in scalar, binary, and product quantization options.Also supports quantization, with its own configuration model.
Hybrid search via the Query API's fusion methods (RRF, DBSF).Hybrid search natively supported, with its own fusion/ranking approach.

Both are commonly shortlisted together for production RAG systems, and the practical choice often comes down to team familiarity, specific quantization or filtering feature needs, and how a team prefers to model its data — more schema-flexible (Qdrant's payload style) versus more explicitly schema-driven (Weaviate's class style).

What language is Weaviate's core primarily written in?
What data modeling style does Weaviate encourage compared to Qdrant?

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What is Qdrant? What is the purpose of Qdrant? What are the key features of Qdrant? What is a collection in Qdrant? What is a point in Qdrant? What is a payload in Qdrant? What is the HNSW algorithm? What distance metrics does Qdrant support? How do you create a collection in Qdrant? How do you insert/upsert points into a collection? What is the difference between REST and gRPC APIs in Qdrant? What client libraries are available for Qdrant? What is payload filtering in Qdrant? Define scalar quantization in Qdrant? What is a segment in Qdrant? How do you perform a similarity search in Qdrant? What is the purpose of a payload index? List the supported field types for payload indexing? What is Qdrant Cloud? What is memmap storage in Qdrant? What is the difference between Qdrant and Pinecone? What is the difference between Qdrant and Weaviate? Why is Qdrant implemented in Rust? How does the HNSW graph work internally in Qdrant? What is the difference between scalar, binary, and product quantization? Explain the internal working of binary quantization and why it's fast? What is oversampling and rescoring in quantized search? How does Qdrant implement filtering during HNSW traversal? Explain the internal working of Qdrant's sharding and replication? What consensus protocol does Qdrant use for distributed clusters, and how does it work? What are named vectors, and when should you use them? What are sparse vectors in Qdrant? Explain hybrid search using the Query API and Prefetch? What is Reciprocal Rank Fusion (RRF) versus Distribution-Based Score Fusion (DBSF)? How do you implement multitenancy in Qdrant? Explain the lifecycle of a write operation in Qdrant (WAL, segments, optimizers)? What is the role of the Write-Ahead Log (WAL) in Qdrant? How do you take and restore snapshots in Qdrant? What is the difference between keeping vectors on-disk versus the HNSW index in RAM? Explain the execution flow of a filtered vector search query in Qdrant? When should you choose binary quantization versus scalar quantization? How do you optimize Qdrant for high-throughput production workloads? What is the ACORN-1 method, and why does it matter for filtered search? Explain the internal working of Qdrant's segment optimizer/merging? How do you implement multi-vector (late interaction / ColBERT-style) search in Qdrant? What is the role of the payload index in query planning? How does Qdrant handle consistency during a node failure? Explain the execution flow of a RAG pipeline built with Qdrant as the retrieval layer? What are the trade-offs of self-hosting Qdrant versus using Qdrant Cloud? What is Qdrant's Discovery/Recommendation API used for?
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