[SPARK-2365] Add IndexedRDD, an efficient updatable key-value store

• Type: New Feature
• Status: Closed
• Priority: Major
• Resolution: Later
• Component/s: GraphX, Spark Core
• Assignee: Ankur Dave
• Reporter: Ankur Dave
• Created: 04/Jul/14 03:23
• Updated: 14/Sep/16 03:26
• Resolved: 17/Dec/15 06:43

Description

RDDs currently provide a bulk-updatable, iterator-based interface. This imposes minimal requirements on the storage layer, which only needs to support sequential access, enabling on-disk and serialized storage.

However, many applications would benefit from a richer interface. Efficient support for point lookups would enable serving data out of RDDs, but it currently requires iterating over an entire partition to find the desired element. Point updates similarly require copying an entire iterator. Joins are also expensive, requiring a shuffle and local hash joins.

To address these problems, we propose IndexedRDD, an efficient key-value store built on RDDs. IndexedRDD would extend RDD[(Long, V)] by enforcing key uniqueness and pre-indexing the entries for efficient joins and point lookups, updates, and deletions.

It would be implemented by (1) hash-partitioning the entries by key, (2) maintaining a hash index within each partition, and (3) using purely functional (immutable and efficiently updatable) data structures to enable efficient modifications and deletions.

GraphX would be the first user of IndexedRDD, since it currently implements a limited form of this functionality in VertexRDD. We envision a variety of other uses for IndexedRDD, including streaming updates to RDDs, direct serving from RDDs, and as an execution strategy for Spark SQL.

Issue Links

• incorporates: SPARK-1955 VertexRDD can incorrectly assume index sharing
• links to: [Github] Pull Request #1297 (ankurdave)
• links to: IndexedRDD on Spark Packages

Sub-Tasks

• Support for arbitrary key types in IndexedRDD: Resolved
• Extract IndexedRDD interface: Resolved
• Add log-structured updates with merge: Resolved
• Add a non-updatable implementation for read performance: Resolved
• Batch multiput updates within partitions: Resolved
• Move IndexedRDD from a pull request into a separate repository: Resolved