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Database / Qdrant Vector DB Interview questions

What are the key features of Qdrant?

Qdrant combines a set of capabilities focused specifically on production-grade vector search, several of which distinguish it from simpler embedded or prototype-focused vector stores.

FeatureWhat it Provides
HNSW indexingFast approximate nearest neighbor search over high-dimensional vectors
Payload filteringStructured metadata filters combined directly with vector search
QuantizationScalar, binary, and product quantization to reduce memory footprint
Distributed deploymentSharding and replication for horizontal scale and fault tolerance
Hybrid searchCombining dense and sparse vectors via the Query API's fusion methods
SnapshotsPoint-in-time backups of collections for recovery and migration

Taken together, these features are aimed at taking an application from an initial prototype (a single Qdrant instance on a laptop) through to a production deployment handling millions or billions of vectors across a replicated, sharded cluster, without switching to a different underlying system along the way.

What does quantization primarily help reduce in Qdrant?
What enables horizontal scale and fault tolerance in 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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