Hyper performant kNN using Annoy for Apache Spark. For some backgrorund reading, I recommend this good-read by Mridang Agarwalla https://medium.com/@mridang.agarwalla/f4757b2b10eb
Unfortunately, Spartann is not available in any public Maven repositories except the GitHub Package Registry. For more information on how to install packages from the GitHub Package Registry, https://docs.github.com/en/packages/guides/configuring-gradle-for-use-with-github-packages#installing-a-package
The usage of Annoy is simple. Spartann accepts a dataset of identifier and vector pairs. To take the simplest object.
case class Book(isbn: String, features: Array[Double]) extends Embeddings[String]
All classes must implement the Embeddings[T] interface where T is the identifer of the object. T in this case is a String but may be anything. You must also specify the Annoy configuration.
final val annoyConfig: AnnoyConfig = AnnoyConfig(50, 256, annoy4s.Euclidean)
AnnoyConfig accepts the number of trees, the dimensionality of the the data and the distance algorithm. An increase in the dimensionality or the number of tress will also degrade performance.
Annoy indexes all items with a non-negative integer value and allocates memory for max(i)+1 items. As shown in both examples, the iterators are zipped so that each item is indexed. The order of the items is not relevant.
Assume you have a dataset of Dataset[Book] and you need to find the similar books published by a publisher.
val records: List[Book] = List(...)
sqlContext.createDataset(records)(Encoders.kryo[Book])
.mapPartitions((books: Iterator[Book]) => {
val vectors: Iterator[(Long, Book)] = books.zipWithIndex.map(_.swap)
.map(item => (item._1.toLong, item._2))
Annoyer.create(vectors, annoyConfig = annoyConfig, verbose = false, maxResults = 50)
})(Encoders.kryo[Neighbour[String]])
.show()
⚠ SpartAnn has been tested with mapPartitions and the code currently lacks comprehensive tests against mapGroups.
Assume you have a dataset of RDD[Book] and you need to find the similar books published by a publisher.
sc.parallelize(..)
.mapPartitions((books: Iterator[Book]) => {
val vectors: Iterator[(Long, Book)] = books.zipWithIndex.map(_.swap)
.map(item => (item._1.toLong, item._2))
Annoyer.create(vectors, annoyConfig = annoyConfig, verbose = false, maxResults = 50)
})
The current implementation doesn't allow on-disk Annoy indexes. Any upstream pull-requests that allow persisting indexes onto HDFS are welcome.
The current implemenntation doesn't allow querying the nearest neighbours by vectors as represented by the API method get_nns_by_vector.
The current implementation doesn't allow querying the distances between two items as represented by the API method get_distance.
Methods such as setting the seed using set_seed(int), querying the number of items using get_n_items(), querying the number of trees using get_n_trees() were deemed superflous and removed from SpartAnn. In the event that these are needed, upstream pull-requests are welcomed.
- Mridang Agarwalla mridang@nosto.com
Apache-2.0 License