API Endpoint

The foundation of any endpoint is its address. The Base URL (e.g., https://api.vectordb.com) specifies the server location. The Path (e.g., /v1/collections/{id}/query) identifies the specific resource or operation. Paths often include path parameters (like {id}) to target specific database entities such as a particular collection or vector ID.

The HTTP verb defines the action to be performed on the resource identified by the endpoint path. Core methods for vector databases include:

• POST: Create resources (e.g., insert vectors, create a collection).
• GET: Retrieve data (e.g., fetch a vector by ID, get collection info).
• PUT/PATCH: Update resources (e.g., modify metadata, upsert vectors).
• DELETE: Remove resources (e.g., delete a vector or collection). The method is a fundamental contract; using GET for a data insertion will fail.

This defines the exact structure of data exchanged. The Request Schema specifies the required payload format for operations like inserting vectors, including fields for the vector array, id, and metadata object. The Response Schema defines the structure returned, such as a list of nearest neighbors with their IDs, distances, and metadata. These schemas are often formally described using OpenAPI Specification or Protocol Buffers.

Headers convey metadata about the request or response. Critical headers for vector database endpoints include:

• Authorization: Contains the API Key or Bearer token (e.g., Authorization: Bearer sk_123abc).
• Content-Type: Declares the media type of the request body (e.g., application/json).
• User-Agent: Identifies the client software. Headers are also used for advanced security protocols like mTLS (Mutual TLS) for certificate-based authentication.

These are key-value pairs appended to the endpoint URL (after a ?) to modify the request. They are used for optional, non-hierarchical instructions. Common examples in vector search include:

• top_k=10: Limit the number of nearest neighbors returned.
• include_metadata=true: Control whether metadata is included in results.
• ef_search=64: Tune the search accuracy/performance trade-off for HNSW indexes. Unlike path parameters, query parameters are often optional and order-independent.

The HTTP status code is the server's immediate response about the request's outcome. Standard codes include:

• 200 OK: Success.
• 201 Created: Resource successfully created.
• 400 Bad Request: Client error (invalid payload).
• 429 Too Many Requests: Rate limiting triggered.
• 500 Internal Server Error: Server-side failure. Accompanying error responses provide a structured payload with a error code, message, and sometimes a trace_id for debugging, allowing clients to implement robust retry logic.

A REST API is an architectural style for a vector database interface that uses standard HTTP methods (GET, POST, PUT, DELETE) and resource-oriented URLs (like /v1/collections/{id}) to perform operations. It is stateless, cacheable, and relies on HTTP status codes for communication, making it the most common and interoperable API design for web-based integrations.

• Key Methods: POST /vectors to insert, GET /vectors/search to query.
• Advantages: Simple, human-readable, and widely supported by all programming languages and tools.
• Use Case: The primary interface for most public-facing vector database services and web applications.

A gRPC API is a high-performance, schema-driven interface that uses the HTTP/2 protocol and Protocol Buffers (protobuf) for efficient, low-latency binary serialization. It is ideal for internal service-to-service communication where speed and bandwidth efficiency are critical.

• Core Features: Strongly-typed contracts, bidirectional streaming, and built-in connection multiplexing.
• Performance: Typically offers lower latency and higher throughput than REST for large-scale or real-time vector operations.
• Use Case: Internal microservices within a data platform that require frequent, high-volume vector ingestion and search.

A Client SDK (Software Development Kit) is a language-specific library that provides a high-level abstraction over raw API endpoint calls. It handles connection management, serialization, and error handling, simplifying developer interaction with a vector database.

• Common Abstractions: Provides objects like Collection, Index, and Query with intuitive methods.
• Built-in Features: Often includes connection pooling, retry logic with exponential backoff, and request timeouts.
• Example: A Python SDK might offer a client.search(vectors=[...], top_k=10) method that constructs and sends the underlying HTTP request to the /search endpoint.

An API Gateway is an intermediary service that sits in front of one or more vector database API endpoints. It acts as a unified entry point, handling cross-cutting concerns so the core database service remains focused on data operations.

• Primary Functions: Request routing, authentication/authorization, rate limiting, request/response transformation, and monitoring.
• Security Role: Centralizes enforcement of API key validation, OAuth 2.0 flows, and mTLS termination.
• Operational Benefit: Enables versioning, canary deployments, and provides a single point for analytics and logging.

The Request Payload is the structured data (typically JSON or protobuf) sent in the body of an API request. For a vector database, this includes vectors, metadata, and query parameters. Idempotency is a critical property of certain API operations where making the same request multiple times yields the same result as making it once.

• Payload Example: A POST /vectors payload contains an array of vectors and their associated IDs and metadata.
• Idempotent Operations: A PUT /vectors/{id} or a delete operation. This is crucial for reliable retries in distributed systems.
• Non-Idempotent Warning: A standard POST to create a resource is not idempotent; submitting it twice may create two identical vectors.

Rate Limiting is a control mechanism that restricts the number of requests a client can make to an endpoint within a time window (e.g., 1000 requests per minute). API Versioning is the practice of managing breaking changes to the API interface by assigning version identifiers to endpoints (e.g., /v1/ vs. /v2/).

• Rate Limit Purpose: Prevents abuse, ensures fair usage, and protects backend services from being overwhelmed.
• Versioning Strategies: Path-based (/v1/search), header-based, or query parameter. Path-based is most common for clarity.
• Stability: Versioning allows developers to upgrade on their own schedule, while deprecated endpoints follow a sunset policy.