Feature management plays an important role in the AI(artificial intelligence) pipeline. Feature stores are designed to offer effective versioning of features during the model training and inference stages. Feature stores must ensure real-time feature updates and version management to collaborate with the upstream data ingestion tasks and power the model serving system. In AI-powered online decision augmentation applications, the model serving system responds to requests in real time to provide better user experience, and feature stores face the challenge of low-latency online feature retrieval. Focusing on this challenge, we developed FeaDB, an in-memory based multi-version online feature store, which adopts a time series model and provides feature versioning semantics to automatically manage features from ingestion to serving. Moreover, an append-write operation was applied to ensure ingestion performance, and version indexing was optimized to improve read operations. A snapshot mechanism is proposed, and it was experimentally proven that snapshot read operations improve performance of lookup and range lookup.