Vespa - Yahoo's big data serving engine

Vespa is an engine for low-latency computation over large data sets. It stores and indexes your data such that queries, selection and processing over the data can be performed at serving time. Vespa is serving platform for Yahoo.com, Yahoo News, Yahoo Sports, Yahoo Finance, Yahoo Gemini, Flickr.

Queries can use both structured filters and unstructured text search to select data. All the matching data is then ranked according to a ranking function - typically machine learned - to implement such use cases as search relevance, recommendation, targeting and personalization.

Vespa is scalable. System sizes up to hundreds of nodes handling tens of billions of documents are not uncommon, and no harder to set up and modify than single node systems. Since all system components, as well as stored data is redundant and self-correcting, hardware failures are not operational emergencies and can be handled by re-adding capacity when convenient.

Its feature include:

• Text search - Combine structured query and text search to select data
• Advanced Ranking - Machine learned ranking
• Aggregation
• Elastic, Scalable
• High Availability
• Auto repair data corruption
• Simple HTTP API interface 
• lot more...