  Visual instance search involves retrieving from a collection of images the
ones that contain an instance of a visual query. Systems designed for visual
instance search face the major challenge of scalability: a collection of a few
million images used for instance search typically creates a few billion
features that must be indexed. Furthermore, as real image collections grow
rapidly, systems must also provide dynamicity, i.e., be able to handle on-line
insertions while concurrently serving retrieval operations. Durability, which
is the ability to recover correctly from software and hardware crashes, is the
natural complement of dynamicity. Durability, however, has rarely been
integrated within scalable and dynamic high-dimensional indexing solutions.
This article addresses the issue of dynamicity and durability for scalable
indexing of very large and rapidly growing collections of local features for
instance retrieval. By extending the NV-tree, a scalable disk-based
high-dimensional index, we show how to implement the ACID properties of
transactions which ensure both dynamicity and durability. We present a detailed
performance evaluation of the transactional NV-tree: (i) We show that the
insertion throughput is excellent despite the overhead for enforcing the ACID
properties; (ii) We also show that this transactional index is truly scalable
using a standard image benchmark embedded in collections of up to 28.5 billion
high-dimensional vectors; the largest single-server evaluations reported in the
literature.
