16.2.2 Storing a Graph Snapshot on Disk

After reading a graph into memory, you can make any changes to the graph (such as running the PageRank algorithm and storing the values as vertex properties), and then store this snapshot of the graph on disk.

If you want to save the state of the graph in memory, then a snapshot of a graph can be saved as a file in binary format (PGB file).

In general, if you must shut down the graph server, then it is recommended that you store all the graph queries and analytics APIs that have been run on the graph. Once the graph server (PGX) is restarted, you can reload the graph and rerun the APIs.

However, if you must save the state of the graph, then the following example explains how to store the graph snapshot on disk.

As a prerequisite for storing the graph snapshot, you need to explicitly authorize access to the corresponding directories by defining a directory object pointing to the directory (on the graph server) that contains the files to read or write.

CREATE OR REPLACE DIRECTORY pgx_file_location AS '<path_to_dir>';
GRANT READ, WRITE ON directory pgx_file_location to GRAPH_DEVELOPER;

Also, note the following:

• The directory in the CREATE DIRECTORY statement must exist on the graph server (PGX).
• The directory must be readable (and/or writable) at the OS level by the graph server (PGX).

The preceding code grants the privileges on the directory to the GRAPH_DEVELOPER role. However, you can also grant permissions to an individual user:

GRANT READ, WRITE ON DIRECTORY pgx_file_location TO <graph_user>;

You can then run the following code to load a PGQL property graph into the graph server (PGX) and save the graph snapshot as a file. Note that multiple PGB files will be generated, one for each vertex and edge provider in the graph.

opg4j> var g = session.readGraphByName("BANK_GRAPH", GraphSource.PG_VIEW)
g ==> PgxGraph[name=BANK_GRAPH_NEW,N=999,E=4993,created=1676021791568]

opg4j> analyst.pagerank(graph)
$8 ==> VertexProperty[name=pagerank,type=double,graph=BANK_GRAPH]

// Now save the state of this graph
opg4j>  var storedPgbConfig = graph.store(ProviderFormat.PGB, "<path_to_dir>")

In a three-tier deployment, the file is written on the server-side file system. You must also ensure that the file location to write is specified in the graph server (PGX). (As explained in Three-Tier Deployments of Oracle Graph with Autonomous Database, in a three-tier deployment, access to the PGX server file system requires a list of allowed locations to be specified.)