Parent-child in Vespa

Vespa's new parent-child feature allows for efficient modeling of hierarchical data relationships, providing a middle ground between the traditional relational database approach and the scalability-focused NoSQL model. This feature is particularly beneficial for cases where data can be represented as a directed acyclic graph, such as in a hypothetical startup serving cat picture advertisements, where Advertisers have multiple Campaigns, each with multiple Ads. Parent-child relationships enable faster updates across related data points, like campaign budgets, by using reference fields and imported fields instead of conventional joins, which are challenging to scale. While this approach incurs a minor performance penalty during search queries, it significantly speeds up data updates and avoids the complexities of maintaining denormalized data models. Vespa's implementation contrasts with ElasticSearch by offering real-time parent-child reference management without the need for manual shard management or experiencing significant query slowdowns. Despite some limitations, such as the inability to query parents based on child properties, Vespa's parent-child feature is a powerful tool for applications requiring scalable, hierarchical data modeling.