14.8.2 Creating a Snapshot via Refreshing

You can create a snapshot via refreshing by performing the following steps:

1. Create a session and load the graph into memory.
2. Check the available snapshots of the graph with PgxSession.getAvailableSnapshots() method.
   • JShell
   • Java
   • Python

   opg4j> session.getAvailableSnapshots(G)
   ==> GraphMetaData [getNumVertices()=4, getNumEdges()=4, memoryMb=0, dataSourceVersion=1453315103000, creationRequestTimestamp=1453315122669 (2016-01-20 10:38:42.669), creationTimestamp=1453315122685 (2016-01-20 10:38:42.685), vertexIdType=integer, edgeIdType=long]

   Deque<GraphMetaData> snapshots = session.getAvailableSnapshots(G);
   for( GraphMetaData metaData : snapshots ) {
     System.out.println( metaData );
   }

   snapshots = session.get_available_snapshots(G)
   for metadata in snapshots:
       print(metadata)

3. Edit the source file to contain an additional vertex and an additional edge or insert two rows in the database.
4. Reload the updated graph within the same session as you loaded the original graph. A new snapshot is created.
   • JShell
   • Java
   • Python

   opg4j> var G = session.readGraphWithProperties( G.getConfig(), true )
   ==> PGX Graph named 'sample_2' bound to PGX session 'a1744e86-65fb-4bd1-b2dc-5458b20954a9' registered at PGX Server Instance running in embedded mode
   opg4j> session.getAvailableSnapshots(G)
   ==> GraphMetaData [getNumVertices()=4, getNumEdges()=4, memoryMb=0, dataSourceVersion=1453315103000, creationRequestTimestamp=1453315122669 (2016-01-20 10:38:42.669), creationTimestamp=1453315122685 (2016-01-20 10:38:42.685), vertexIdType=integer, edgeIdType=long]
   ==> GraphMetaData [getNumVertices()=5, getNumEdges()=5, memoryMb=3, dataSourceVersion=1452083654000, creationRequestTimestamp=1453314938744 (2016-01-20 10:35:38.744), creationTimestamp=1453314938833 (2016-01-20 10:35:38.833), vertexIdType=integer, edgeIdType=long]

   G = session.readGraphWithProperties( G.getConfig(), true );
   
   Deque<GraphMetaData> snapshots = session.getAvailableSnapshots( G );

   G = session.read_graph_with_properties(G.config,update_if_not_fresh=True)

   Note that there are two GraphMetaData objects in the call for available snapshots, one with 4 vertices and 4 edges and one with 5 vertices and 5 edges.
5. Verify that the graph variable points to the newly loaded graph using getNumVertices() and getNumEdges() methods.
   • JShell
   • Java
   • Python

   opg4j> G.getNumVertices()
   ==> 5
   opg4j> G.geNumEdges()
   ==> 5

   int vertices = G.getNumVertices();
   long edges = G.getNumEdges();

   vertices = G.num_vertices
   edges = G.num_edges