The Dgraph uses data structures and algorithms to issue real-time responses to queries.
The Dgraph stores the ingested data in the Dgraph databases it creates for the indexed data sets. The Dgraph receives client requests from Studio, queries its databases, and returns the results. The Dgraph is stateless. This design requires that a complete query is sent to it for each request. The stateless design facilitates the addition of Dgraph instances for load balancing and redundancy. Any instance of a Dgraph can reply to queries independently of other instances.
A Big Data Discovery cluster can include two or more Dgraph instances. They handle end-user query requests and store Dgraph databases on shared storage. For each data set, the leader Dgraph (once it is automatically appointed in BDD) handles all write operations, such as updates and configuration changes to that data set. The remaining Dgraphs serve as read-only followers for that data set. The Dgraph Gateway performs the routing of requests to the Dgraph nodes. It handles query caching, business logic, and cluster services for the Dgraph nodes.
The deployment of Dgraphs occurs at the installation time. For information, see the Installation Guide.
The Dgraph Tracing Utility
The Dgraph Tracing Utility is a Dgraph diagnostic program used by Oracle Support. It stores the Dgraph trace data, which are useful in troubleshooting the Dgraph. It starts when the Dgraph starts and keeps track of all Dgraph operations. It stops when the Dgraph shuts down. You can save and download trace data to share it with Oracle Support.
The bdd-admin script
Use the bdd-admin script to run administrative operations on the BDD cluster deployment, such as starting components, backing up, restoring, and updating the configuration. For information on the bdd-admin script, see the Administrator's Guide.
The Dgraph HDFS Agent
The Dgraph HDFS Agent loads data into the Dgraph. It reads the Avro files from the data processing workflow and formats them for data loading. It then sends them to the Dgraph. For information on the Dgraph HDFS Agent, see the Data Processing Guide.