Isolation Levels

Read Committed Snapshot Isolation

Read-Only Queries are evaluated under Snapshot Isolation. Mutation Queries (i.e. write queries) are executed under Read Committed isolation.

Query Interface

SPARQL Gremlin

Neptune supports both Gremlin and SPARQL. Specifically, Neptune supports three Gremlin variants:

• Gremlin-Groovy
• Gremlin-Java
• Gremlin-Python

Concurrency Control

Multi-version Concurrency Control (MVCC)

Read-Only queries are evaluated under snapshot isolation. That is, read-only queries operate on a single consistent snapshot of the database which is taken right when the query begins. Snapshot isolation is achieved via multiversion concurrency control and guarantees that dirty reads, non-repeatable reads, and phantom reads do not occur. Read-Only queries may be performed on read replicas causing a small replication lag between the given query results and what the result should be.

For Mutation Queries (i.e. write queries), Neptune locks records and ranges of records when reading data. This ensures consistency of data.

Foreign Keys

Supported

The edges/relationships in the graph are foreign keys.

Indexes

Hash Table

Neptune maintains three indices on quads:

• SPOG - Key composed of Subject + Predicate + Object + Graph
• POGS - Key composed of Predicate + Object + Graph + Subject
• GPSO - Key composed of Graph + Predicate + Subject + Object

Amazon Neptune uses Hash Tables for its indexes.

Storage Model

Custom

Neptune stores data as a Neptune Quad.

Data Model

Graph Triplestore / RDF

Neptune uses four-position (quad) element called a Neptune Quad. A Neptune quad is composed of a subject, predicate, object, and a graph identifier. A quad is an assertion about one or more resources. For example, an edge is described by a quad and so is each property of a node. A graph is a set of quad statements with the same graph identifier.

System Architecture

Shared-Disk

Data is stored in a cluster volume which is a single, virtual volume on solid-state disks.

Compression

Naïve (Page-Level)

Neptune supports compression of single files using the gzip format.

Storage Architecture

Disk-oriented

Neptune utilizes Amazon S3 to store data.

Joins

Hash Join Sort-Merge Join

Query Compilation

Code Generation