27 August 2026

#FAISS


Key Concepts


S.No Topic Sub topic
1 FAISS Fundamentals Facebook AI Similarity Search, vector similarity, embeddings, nearest-neighbor search, index, Top-K, use cases
2 Installation & Setup faiss-cpu , faiss-gpu , Python installation, environment setup, NumPy integration, GPU setup, version compatibility
3 Vectors & Embeddings Dense vectors, embedding models, dimensions, float32, normalization, query vectors, document vectors
4 Similarity Metrics L2 distance, inner product, cosine similarity, normalized vectors, metric selection, distance interpretation, ranking
5 Exact Search Brute-force search, exhaustive search, IndexFlatL2 , IndexFlatIP , exact nearest neighbors, Top-K, baseline evaluation
6 Index Architecture FAISS index classes, training, adding vectors, searching, index parameters, index factory, index composition
7 IndexFlat IndexFlatL2 , IndexFlatIP , exact search, memory usage, search speed, reconstruction, use cases
8 IVF Index IndexIVFFlat , inverted file, coarse quantizer, nlist , nprobe , training, search
9 IVF Optimization nlist tuning, nprobe tuning, recall, latency, memory, training dataset, performance
10 HNSW IndexHNSWFlat , graph search, M , efConstruction , efSearch , recall, latency
11 HNSW Optimization Graph parameters, M tuning, efConstruction, efSearch, memory, index build time, search performance
12 Product Quantization PQ, IndexPQ , sub-vectors, codebooks, compression, quantization error, memory reduction
13 IVF-PQ IndexIVFPQ , coarse quantization, product quantization, nlist , nprobe , code size, recall
14 Scalar Quantization IndexScalarQuantizer , INT8, FP16, compression, memory optimization, precision, performance
15 Binary Indexing Binary vectors, Hamming distance, binary indexes, bit representation, memory efficiency, search, use cases
16 GPU Acceleration GPU indexes, StandardGpuResources , CPU-to-GPU transfer, GPU search, GPU memory, multi-GPU, performance
17 Index Factory index_factory , index strings, Flat, IVF, HNSW, PQ, composite indexes
18 Index Training train() , training vectors, clustering, centroids, training size, retraining, training quality
19 Add & Search add() , add_with_ids() , search() , query vectors, Top-K, distances, labels
20 ID Management IndexIDMap , IndexIDMap2 , custom IDs, integer IDs, vector mapping, retrieval, ID persistence
21 Metadata Management External metadata, ID mapping, document IDs, payload storage, relational storage, JSON metadata, result enrichment
22 Index Persistence write_index() , read_index() , index serialization, loading indexes, backups, portability, version compatibility
23 Incremental Updates Adding vectors, removing vectors, remove_ids() , index updates, rebuilding, synchronization, lifecycle management
24 Filtering Metadata filtering, pre-filtering, post-filtering, ID filtering, external filtering, limitations, hybrid approaches
25 Range Search range_search() , distance threshold, radius search, result boundaries, similarity threshold, memory usage, use cases
26 Batch Search Batch queries, batch insertion, NumPy arrays, vectorized operations, throughput, memory management, optimization
27 LangChain Integration FAISS vector store, embeddings, similarity search, retrievers, metadata, persistence, RAG
28 LlamaIndex Integration FAISS vector store, VectorStoreIndex, embeddings, nodes, retrievers, query engine, RAG
29 RAG Pipeline Document loading, chunking, embeddings, FAISS indexing, retrieval, reranking, LLM generation
30 Performance & Production Recall@K, latency, throughput, memory optimization, CPU/GPU scaling, index selection, production RAG architecture

Interview question

What is FAISS?
What problem does FAISS solve?
What is a vector index in FAISS?
What is vector similarity search?
What is nearest neighbor search?
What is approximate nearest neighbor search?
What is exact nearest neighbor search?
What is an embedding vector?
What is vector dimensionality?
What is vector space?
What is cosine similarity?
What is Euclidean distance in FAISS?
What is inner product in FAISS?
What is L2 distance?
What is IndexFlatL2?
What is IndexFlatIP?
What is IndexFlatCodes?
What is IndexHNSWFlat?
What is IndexIVFFlat?
What is IndexIVFPQ?
What is IndexIVFSQ?
What is IndexPQ?
What is IndexLSH?
What is IndexScalarQuantizer?
What is IndexBinaryFlat?
What is IndexBinaryIVF?
What is an IVF index?
What is an inverted file index?
What is a centroid in FAISS?
What is clustering in FAISS?
What is k-means in FAISS?
What is IndexIVF?
What is nlist in FAISS?
What is nprobe in FAISS?
What is product quantization?
What is PQ?
What is OPQ?
What is Optimized Product Quantization?
What is residual quantization?
What is scalar quantization?
What is binary quantization?
What is vector compression?
What is vector reconstruction?
What is add() in FAISS?
What is add_with_ids() in FAISS?
What is search() in FAISS?
What is range_search() in FAISS?
What is train() in FAISS?
What is is_trained in FAISS?
What is ntotal in FAISS?
What is d in FAISS?
What is IndexIDMap?
What is IndexIDMap2?
What is IndexShards?
What is IndexReplicas?
What is IndexPreTransform?
What is IndexRefineFlat?
What is a composite FAISS index?
What is an index factory in FAISS?
What is the FAISS index factory string?
What is IndexFlat?
What is IndexIVFFlat's training requirement?
What is the role of training vectors in FAISS?
What is a training set for FAISS?
What is search recall in FAISS?
What is search latency in FAISS?
What is throughput in FAISS?
What is memory footprint in FAISS?
What is vector normalization in FAISS?
What is cosine search using inner product?
What is the relationship between cosine similarity and normalized vectors?
What is top-k search in FAISS?
What is k in FAISS search?
What is the distance output of FAISS search?
What are labels returned by FAISS search?
What is a deleted vector in FAISS?
What is IndexIVF deletion?
What is DirectMap in FAISS?
What is remove_ids()?
What is reconstruct()?
What is reconstruct_n()?
What is search_and_reconstruct()?
What is write_index()?
What is read_index()?
What is FAISS index serialization?
What is FAISS persistence?
What is memory-mapped FAISS index loading?
What is GPU support in FAISS?
What is a FAISS GPU index?
What is CPU-GPU index transfer?
What is GpuIndexFlatL2?
What is GpuIndexFlatIP?
What is GPU resource management in FAISS?
What is multi-GPU FAISS?
What is FAISS batch search?
What is batched vector insertion?
What is parallel search in FAISS?
What is OpenMP in FAISS?
What is FAISS threading?
What is FAISS for RAG?
What is FAISS in a retrieval pipeline?
What is FAISS with LangChain?
What is FAISS with LlamaIndex?
What is FAISS with sentence-transformers?
What is FAISS with OpenAI embeddings?
Why use FAISS?
Why use FAISS for vector similarity search?
Why is FAISS fast?
Why use approximate nearest neighbor search?
Why use exact nearest neighbor search?
Why choose IndexFlatL2?
Why choose IndexFlatIP?
Why use HNSW?
Why use IVF?
Why use IVFFlat?
Why use IVFPQ?
Why use Product Quantization?
Why use OPQ?
Why use scalar quantization?
Why use binary indexes?
Why normalize vectors for cosine search?
Why use inner product for normalized embeddings?
Why train an IVF index?
Why does FAISS require training for some indexes?
Why choose an appropriate nlist value?
Why tune nprobe?
Why does increasing nprobe improve recall?
Why does increasing nprobe increase latency?
Why use Product Quantization for large datasets?
Why compress vectors?
Why use IndexRefineFlat?
Why use IndexPreTransform?
Why use IndexIDMap?
Why use custom vector IDs?
Why persist a FAISS index?
Why use memory-mapped indexes?
Why use GPU acceleration?
Why use multiple GPUs?
Why batch FAISS queries?
Why batch vector insertion?
Why use OpenMP?
Why use FAISS for RAG?
Why use FAISS with sentence-transformers?
Why use FAISS with LangChain?
Why use FAISS with LlamaIndex?
Why use FAISS for semantic search?
Why use FAISS for recommendation systems?
Why use FAISS for image similarity?
Why use FAISS for duplicate detection?
Why use FAISS for clustering-related retrieval?
Why is memory usage important in FAISS?
Why is recall important in approximate search?
Why is latency important in vector retrieval?
Why should the training dataset represent production vectors?
Why should embedding dimensions remain consistent?
Why should index configuration be versioned?
Why benchmark FAISS before production deployment?
Why use a metadata store alongside FAISS?
When should you use FAISS?
When should you not use FAISS?
When should you use IndexFlatL2?
When should you use IndexFlatIP?
When should you use HNSW?
When should you use IVFFlat?
When should you use IVFPQ?
When should you use PQ?
When should you use OPQ?
When should you use scalar quantization?
When should you use binary indexes?
When should you use exact search?
When should you use approximate search?
When should you normalize embeddings?
When should you use cosine similarity?
When should you use inner product?
When should you use L2 distance?
When should you use range search?
When should you use top-k search?
When should you use IndexIDMap?
When should you use IndexIDMap2?
When should you use DirectMap?
When should you use remove_ids()?
When should you use reconstruct()?
When should you use IndexRefineFlat?
When should you use IndexPreTransform?
When should you use IndexShards?
When should you use IndexReplicas?
When should you train an IVF index?
When should you retrain an IVF or PQ index?
When should you increase nprobe?
When should you decrease nprobe?
When should you increase nlist?
When should you decrease nlist?
When should you increase HNSW search parameters?
When should you use GPU FAISS?
When should you use multi-GPU FAISS?
When should you use batch search?
When should you use memory-mapped indexes?
When should you serialize a FAISS index?
When should you rebuild an index?
When should you use a metadata database with FAISS?
When should you use FAISS for RAG?
When should you use FAISS for recommendations?
When should you use FAISS for image search?
When should you use FAISS for duplicate detection?
When should you consider a distributed vector database instead of FAISS?
When should you shard a FAISS index?
When should you replicate a FAISS index?
When should you benchmark recall?
When should you benchmark latency?
When should you monitor memory consumption?
Which FAISS index should you choose?
Which FAISS index is best for small datasets?
Which FAISS index is best for large datasets?
Which index is best for exact search?
Which index is best for approximate search?
Which is better for your workload, HNSW or IVF?
Which is better, IVFFlat or IVFPQ?
Which distance metric should you choose?
Which index should you use for cosine similarity?
Which index should you use for inner product?
Which index should you use for L2 distance?
Which vector dimension should you choose?
Which embedding model should you choose for FAISS?
Which value of k should you use?
Which nlist value should you choose?
Which nprobe value should you choose?
Which HNSW M value should you choose?
Which HNSW efConstruction value should you choose?
Which HNSW efSearch value should you choose?
Which PQ code size should you choose?
Which number of subquantizers should you choose?
Which quantization method should you choose?
Which precision should you use for embeddings?
Which GPU should you use for FAISS?
Which CPU configuration is suitable for FAISS?
Which metadata database should you use with FAISS?
Which persistence strategy should you use?
Which sharding strategy should you use?
Which replication strategy should you use?
Which batching strategy should you use?
Which training dataset should you use for IVF?
Which vectors should be used to train PQ?
Which index should you use for RAG?
Which index should you use for recommendation systems?
Which index should you use for image similarity?
Which index should you use for high recall?
Which index should you use for low latency?
Which index should you use for low memory?
Which index should you use for billions of vectors?
Which index should you use for frequent updates?
Which index should you use for frequent deletions?
Which FAISS API should you use to add vectors?
Which FAISS API should you use to search vectors?
Which FAISS API should you use to remove vectors?
Which FAISS API should you use to save an index?
Which FAISS API should you use to load an index?
Which FAISS wrapper should you use with LangChain?
Which embedding library works well with FAISS?
Which monitoring metrics should you track?
Which evaluation metrics should you use for vector retrieval?
How does FAISS work?
How does exact nearest neighbor search work in FAISS?
How does approximate nearest neighbor search work?
How does IndexFlatL2 work?
How does IndexFlatIP work?
How does HNSW work in FAISS?
How does IVFFlat work?
How does IVFPQ work?
How does Product Quantization work?
How does OPQ work?
How does scalar quantization work?
How does k-means training work in FAISS?
How does FAISS select IVF centroids?
How does nlist affect search?
How does nprobe affect search?
How does HNSW affect recall and latency?
How does vector normalization enable cosine search?
How does FAISS calculate distance?
How does FAISS return top-k results?
How does range search work?
How do you install FAISS?
How do you create a FAISS index?
How do you add vectors to FAISS?
How do you add vectors with custom IDs?
How do you search vectors in FAISS?
How do you perform cosine similarity search?
How do you perform L2 search?
How do you perform inner-product search?
How do you train an IVF index?
How do you choose training vectors?
How do you configure nlist?
How do you configure nprobe?
How do you configure HNSW parameters?
How do you configure PQ?
How do you remove vectors from FAISS?
How do you reconstruct a vector?
How do you save a FAISS index?
How do you load a FAISS index?
How do you memory-map a FAISS index?
How do you move a FAISS index to GPU?
How do you move a GPU index back to CPU?
How do you use multiple GPUs?
How do you shard a FAISS index?
How do you replicate a FAISS index?
How do you batch vector queries?
How do you optimize FAISS search latency?
How do you improve FAISS recall?
How do you reduce FAISS memory usage?
How do you use FAISS in a RAG pipeline?
How do you integrate FAISS with LangChain?
How do you integrate FAISS with LlamaIndex?
How do you integrate FAISS with sentence-transformers?
Where is FAISS used?
Where does FAISS fit in a RAG architecture?
Where should embeddings be generated?
Where should vectors be stored?
Where should metadata be stored when using FAISS?
Where should document IDs be stored?
Where should chunk IDs be stored?
Where should vector indexes be created?
Where should FAISS run in a microservices architecture?
Where should the embedding service run?
Where should document preprocessing happen?
Where should chunking happen?
Where should vector normalization happen?
Where should FAISS training happen?
Where should IVF centroids be trained?
Where should PQ codebooks be trained?
Where should GPU FAISS run?
Where should FAISS indexes be persisted?
Where should FAISS backups be stored?
Where should index versions be stored?
Where should metadata filtering happen?
Where should authorization happen?
Where should tenant isolation happen?
Where should reranking happen?
Where should retrieved context be passed to the LLM?
Where should prompt construction happen?
Where should query caching happen?
Where should embedding caching happen?
Where should duplicate detection happen?
Where should document deletion be handled?
Where should document updates be handled?
Where should index rebuilding happen?
Where should FAISS monitoring happen?
Where should retrieval metrics be collected?
Where should latency metrics be collected?
Where should memory metrics be collected?
Where should GPU metrics be collected?
Where should logs be stored?
Where should failure alerts be configured?
Where should FAISS be used instead of Pinecone?
Where should FAISS be used instead of Qdrant?
Where should FAISS be used instead of pgvector?
Where should FAISS be used instead of Redis Vector Search?
Where should FAISS be used for recommendation systems?
Where should FAISS be used for image search?
Where should FAISS be used for semantic search?
Where should FAISS be used for duplicate detection?
Where should FAISS be used for multimodal retrieval?
Where should FAISS be used for offline batch retrieval?
What is the difference between FAISS and Pinecone?
What is the difference between FAISS and Qdrant?
What is the difference between FAISS and Weaviate?
What is the difference between FAISS and ChromaDB?
What is the difference between FAISS and pgvector?
What is the difference between FAISS and Redis Vector Search?
What is the difference between FAISS and Milvus?
What is the difference between FAISS and Elasticsearch?
What is the difference between HNSW and IVF?
What is the difference between IVFFlat and IVFPQ?
What is the difference between PQ and OPQ?
What is the difference between exact and approximate search?
What is the difference between L2 distance and inner product?
What is the difference between cosine similarity and inner product?
What is the difference between CPU and GPU FAISS?
What is the difference between IndexIDMap and IndexIDMap2?
What is the difference between IndexShards and IndexReplicas?
What is the difference between vector indexing and metadata indexing?
What is the difference between FAISS and a managed vector database?
What is the difference between FAISS and a distributed vector database?
Your FAISS search latency suddenly increases. How would you troubleshoot it?
Your FAISS recall is too low. Which parameters would you investigate?
Your IVFFlat index returns poor results. How would you improve recall?
Your nprobe value is high but recall is still poor. What would you investigate?
Your HNSW index consumes too much memory. How would you optimize it?
Your FAISS index does not fit into RAM. How would you redesign the index?
You need to search 100 million vectors with low latency. Which FAISS index would you choose and why?
You need to search one billion vectors on a limited-memory machine. How would you design the FAISS solution?
You need very high recall with acceptable latency. How would you tune FAISS?
You need extremely low latency for millions of vectors. How would you optimize FAISS?
Your IVF index is not trained. How would you diagnose and fix the problem?
Your production embeddings have a different distribution from your training embeddings. What would you do?
Your embedding dimension changed from 768 to 1536. How would you migrate the FAISS index?
Your application requires frequent vector deletions. How would you design the FAISS data model?
Your application requires frequent vector updates. How would you handle index maintenance?
You need custom document IDs instead of FAISS-generated IDs. How would you implement them?
You need metadata filtering such as tenant, document type, and date. How would you implement it with FAISS?
You need multi-tenant RAG using FAISS. How would you ensure tenant isolation?
You need high availability for a FAISS-based retrieval service. How would you architect it?
Your FAISS process crashes and the in-memory index is lost. How would you recover?
You need zero-downtime FAISS index updates. How would you design index versioning and swapping?
You need to migrate from Pinecone to FAISS with minimal downtime. How would you perform the migration?
Your FAISS RAG system retrieves relevant documents but generates incorrect answers. How would you troubleshoot the complete pipeline?
Design a production-grade FAISS RAG system supporting millions of documents, embeddings, metadata, filtering, HNSW or IVF, persistence, GPU acceleration, multi-tenancy, monitoring, and index updates.
Your FAISS application must support both CPU-only deployments and GPU deployments. How would you design a portable architecture?

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