This page attempts to draw a comparison between Dgraph and other popular graph databases/datastores. The summaries that follow are brief descriptions that may help a person decide if Dgraph will suit their needs.
Batch based graph processing frameworks provide a very high throughput to do periodic processing of data. This is useful to convert graph data into a shape readily usable by other systems to then serve the data to end users.
- Pregel, is a system for large-scale graph processing by Google. You can think of it as equivalent to MapReduce/Hadoop.
- Pregel isn't designed to be exposed directly to users, i.e. run with real-time updates and execute arbitrary complexity queries. Dgraph is designed to be able to respond to arbitrarily complex user queries in low latency and allow user interaction.
- Pregel can be used along side Dgraph for complementary processing of the graph, to allow for queries which would take over a minute to run via Dgraph, or produce too much data to be consumed by clients directly.
Graph databases optimize internal data representation to be able to do graph operations efficiently.
- Neo4j is the most popular graph database according to db-engines.com and has been around since 2007. Dgraph is a much newer graph database built to scale to Google web scale and for serious production usage as the primary database.
- Neo4j is written in Java and supports Cypher and Gremlin query language. Dgraph aims to support GraphQL, a query language created by Facebook. As opposed to Cypher or Gremlin, which produce results in simple list format, GraphQL allows results to be produced in a subgraph format, which has richer semantics. Also, GraphQL supports schema validation which is useful to ensure data correctness during both input and output.
- Neo4j is built similar to MySQL, run on a single machine with a global mutex lock to ensure full ACID-compliant transactional model. Dgraph is a distributed system built for low latency, high throughput query execution. It picks pages from Google's Bigtable and Facebook's Tao, both of which achieve high scalability at the cost of lack of full ACID compliant transactional support. Also see: Dgraph#Note on Transactions
For a more thorough comparison of Dgraph vs Neo4j, you can read our blog.
Graph datastores act like a graph layer above some other SQL/NoSQL database to do the data management for them. This other database is the one responsible for backups, snapshots, server failures and data integrity.
- Both Cayley and Dgraph are written primarily in Go language and inspired from different projects at Google.
- Cayley acts like a graph layer, providing a clean storage interface that could be implemented by various stores, for, e.g., PostGreSQL, RocksDB for a single machine, MongoDB to allow distribution. In other words, Cayley hands over data to other databases. While Dgraph uses RocksDB, it assumes complete ownership over the data and tightly couples data storage and management to allow for efficient distributed queries.
- Cayley's design suffers from high fan-out issues. In that, if intermediate steps cause a lot of results to be returned, and the data is distributed, it would result in many network calls between Cayley and the underlying data layer. Dgraph's design minimizes the number of network calls, to reduce the number of servers it needs to touch to respond to a query. This design produces better and predictable query latencies in a cluster, even as cluster size increases.