GDS Sessions

A GDS Session is a temporary compute environment for running GDS workloads. It is a service offered by Neo4j and runs within Neo4j’s Aura cloud platform. A GDS Session reads data from a Neo4j DBMS through a remote projection, runs computations on the projected graph, and optionally writes the results back to the DBMS using remote write-back.

GDS Sessions are not available by default. Contact your account manager to get the features enabled.

1. GDS Session management

The GdsSessions object is the API entry point to the following operations:

get_or_create: Create a new GDS Session, or connect to an existing one.
list: List all currently active GDS Sessions.
delete: Delete a GDS Session.

You need Neo4j Aura API credentials (CLIENT_ID and CLIENT_SECRET) to create a GdsSessions object. See the Aura documentation for instructions on how to create API credentials from your Neo4j Aura account.

Creating a GdsSessions object:

from graphdatascience.session import GdsSessions, AuraAPICredentials

CLIENT_ID = "my-aura-api-client-id"
CLIENT_SECRET = "my-aura-api-client-secret"

# Create a new GdsSessions object
sessions = GdsSessions(api_credentials=AuraAPICredentials(CLIENT_ID, CLIENT_SECRET))

1.1. Creating a GDS Session

To create a GDS Session, use the get_or_create() method. It will create a new session if it does not exist, or connect to an existing one if it does. If the session options differ from the existing one, an error is thrown.

The return value of get_or_create() is an AuraGraphDataScience object. It offers a similar API to the GraphDataScience object, but it is configured to run on a GDS Session. As a convention, always use the variable name gds for the return value of get_or_create().

1.1.1. Syntax

To create a GDS Session, you need to provide the following information:

Session name. The name must be unique.
Session memory. This configuration determines the amount of memory and CPU available to the session. It also determines the cost of running the session. Available configurations are listed in our API reference. You can use the sessions.estimate() method to estimate the size required.
DBMS connection. This is a DbmsConnectionInfo object that contains the URI of an Neo4j instance, a username, and a password.
TTL. This optional parameter specifies the time-to-live of the session. The session will be automatically deleted if the session was unused for the provided duration. Usage is defined as the computation of an algorithm or the projection of a graph.
Cloud location. This is a CloudLocation object that specifies the cloud provider and region where the GDS Session will run. Required if the DBMS connection is for a self-managed database.

1.1.2. Examples

Creating a GDS Session for an AuraDB instance:

from datetime import timedelta
from graphdatascience.session import DbmsConnectionInfo, AlgorithmCategory

name = "my-new-session"
memory = sessions.estimate(
    node_count=20,
    relationship_count=50,
    algorithm_categories=[AlgorithmCategory.CENTRALITY, AlgorithmCategory.NODE_EMBEDDING],
)
db_connection_info = DbmsConnectionInfo("neo4j+s://mydbid.databases.neo4j.io", "my-user", "my-password")

gds = sessions.get_or_create(
    session_name=name,
    memory=memory,
    db_connection=db_connection_info,
    ttl=timedelta(hours=5),
)

Creating a GDS Session for a self-managed Neo4j database:

from datetime import timedelta
from graphdatascience.session import DbmsConnectionInfo, AlgorithmCategory, CloudLocation

name = "my-new-session-sm"
memory = sessions.estimate(
    node_count=20,
    relationship_count=50,
    algorithm_categories=[AlgorithmCategory.CENTRALITY, AlgorithmCategory.NODE_EMBEDDING],
)
db_connection_info = DbmsConnectionInfo("neo4j://localhost", "my-user", "my-password")
cloud_location = CloudLocation(provider="gcp", region="europe-west1")

gds = sessions.get_or_create(
    session_name=name,
    memory=memory,
    db_connection=db_connection_info,
    ttl=timedelta(hours=5),
    cloud_location=cloud_location,
)

1.2. Listing GDS Sessions

The list() method returns the name and size of memory of all currently active GDS Sessions.

Listing GDS Sessions:

sessions.list()

1.3. Deleting a GDS Session

Use the delete() method to delete a GDS Session. This will terminate the session and stop any running costs from accumulating further. Deleting a session will not affect the configured Neo4j data source. However, any data not written back to the Neo4j instance will be lost.

Deleting a GDS Session:

sessions.delete(session_name="my-new-session")

2. Projecting graphs into a GDS Session

Once you have a GDS Session, you can project a graph into it. This operation is called remote projection because the data source is not a co-located database, but rather a remote one.

You can create a remote projection using the gds.graph.project() endpoint with a graph name, a Cypher query, and additional optional parameters. The Cypher query must contain the gds.graph.project.remote() function to project the graph into the GDS Session.

2.1. Syntax

Remote projection:

gds.graph.project(
    graph_name: str,
    query: str,
    concurrency: int = 4,
    undirected_relationship_types: Optional[List[str]] = None,
    inverse_indexed_relationship_types: Optional[List[str]] = None,
): (Graph, Series[Any])

Table 1. Parameters:
Name	Optional	Default	Description
`graph_name`	no	`-`	Name of the graph.
`query`	no	`-`	Projection query.
`concurrency`	yes	`4`	Concurrency to use for building the graph within the session.
`batch_size`	yes	`10000`	Size of batches transmitted from the DBMS to the session.
`undirected_relationship_types`	yes	`[]`	List of relationship type names that should be treated as undirected.
`inverse_indexed_relationship_types`	yes	`[]`	List of relationship type names that should be indexed in reverse.

Table 2. Results:
Name	Type	Description
`graph`	`Graph`	Graph object representing the projected graph.
`result`	`Series[Any]`	Statistical data about the projection.

The concurrency and batch_size configuration parameters can be used to tune the performance of the remote projection.

The concurrency of the remote projection query is controlled by the Cypher runtime on the DBMS server. Use CYPHER runtime=parallel as a query prefix to maximise performance. The actual concurrency used depends on the DBMS server’s available processors and current operational load.

2.1.1. Remote projection query syntax

The remote projection query supports the same syntax as a Cypher projection, with two key differences:

The graph name is not a parameter. Instead, the graph name is provided to the gds.graph.project() endpoint.
The gds.graph.project.remote() function must be used, instead of the gds.graph.project() function.

For full details and examples on how to write Cypher projection queries, see the Cypher projection documentation in the GDS Manual.

2.1.2. Relationship type undirectedness and inverse indexing

The optional parameters undirectedRelationshipTypes and inverseIndexedRelationshipTypes are used to configure undirectedness and inverse indexing of relationships. These have the same behavior as documented in the GDS Manual.

2.2. Example

This example shows how to project a graph into a GDS Session. The example graph is heterogeneous and models users and products. Users can know each other, and users can buy products. The database connection is to a new, empty AuraDB instance.

Create a GDS Session and add some data to the database:

import os # for reading environment variables
from graphdatascience.session import SessionMemory, DbmsConnectionInfo, GdsSessions, AuraAPICredentials

sessions = GdsSessions(api_credentials=AuraAPICredentials(os.environ["CLIENT_ID"], os.environ["CLIENT_SECRET"]))

db_connection = DbmsConnectionInfo(os.environ["DB_URI"], os.environ["DB_USER"], os.environ["DB_PASSWORD"])
gds = sessions.get_or_create(
    session_name="my-new-session",
    memory=SessionMemory.m_8GB,
    db_connection=db_connection,
)

gds.run_cypher(
    """
    CREATE
     (u1:User {name: 'Mats'}),
     (u2:User {name: 'Florentin'}),
     (p1:Product {name: 'ice cream', cost: 4.2}),
     (p2:Product {name: 'computer', cost: 13.37})

    CREATE
     (u1)-[:KNOWS {since: 2020}]->(u2),
     (u2)-[:BOUGHT {price: 7474}]->(p1),
     (u1)-[:BOUGHT {price: 1337}]->(p2)
    """
)

With the gds GDS Session active, project the graph and specify node and relationship property schemas as follows:

Project a graph into the GDS Session:

G, result = gds.graph.project(
    graph_name="my-graph",
    query="""
    CALL {
        MATCH (u1:User)
        OPTIONAL MATCH (u1)-[r:KNOWS]->(u2:User)
        RETURN u1 AS source, r AS rel, u2 AS target, {} AS sourceNodeProperties, {} AS targetNodeProperties
        UNION
        MATCH (p:Product)
        OPTIONAL MATCH (p)<-[r:BOUGHT]-(user:User)
        RETURN user AS source, r AS rel, p AS target, {} AS sourceNodeProperties, {cost: p.cost} AS targetNodeProperties
    }
    RETURN gds.graph.project.remote(source, target, {
      sourceNodeProperties: sourceNodeProperties,
      targetNodeProperties: targetNodeProperties,
      sourceNodeLabels: labels(source),
      targetNodeLabels: labels(target),
      relationshipType: type(rel),
      relationshipProperties: properties(rel)
    })
    """,
)

3. Running algorithms

You can run algorithms on a remotely projected graph in the same way you would on any projected graph. For instance, you can run the PageRank and FastRP algorithms on the projected graph from the previous example as follows:

Run algorithms and stream back results:

gds.pageRank.mutate(G, mutateProperty="pr")
gds.fastRP.mutate(G, featureProperties=["pr"], embeddingDimension=2, nodeSelfInfluence=0.1, mutateProperty="embedding")

# Stream the results back together with the `name` property fetched from the database
gds.graph.nodeProperties.stream(G, db_node_properties=["name"], node_properties=["pr", "embedding"])

For a full list of the available algorithms, see the API reference.

3.1. Limitations

Model Catalog is supported with limitations:
- Trained models can only be used for prediction using the same Session in which they were trained. After the Session is deleted, all trained models will be lost.
- Model publishing is not supported, including
  - gds.model.publish
- Model persistence is not supported, including
  - gds.model.store
  - gds.model.load
  - gds.model.delete
Topological Link Prediction algorithms are not supported, including
- gds.alpha.linkprediction.adamicAdar
- gds.alpha.linkprediction.commonNeighbors
- gds.alpha.linkprediction.preferentialAttachment
- gds.alpha.linkprediction.resourceAllocation
- gds.alpha.linkprediction.sameCommunity
- gds.alpha.linkprediction.totalNeighbors

4. Remote write-back

The GDS Session’s in-memory graph was projected from data in AuraDB, so write-back operations will persist the data back to the same AuraDB instance. When calling any write operations, the GDS Python client will automatically use the remote write-back functionality. This includes all .write algorithm modes as well as all .write graph operations.

By default, write back will happen concurrently, in one transaction per batch. The behaviour is controlled by three aspects:

the size of the dataset (e.g., node count or relationship count)
the configured batch size
the configured concurrency

4.1. Syntax

Remote graph write-back:

gds.graph.<operation>.write(
    graph_name: str,
    # additional parameters,
    **config: Any,
): Series[Any]

Remote graph write-back:

gds.<algo>.write(
    graph_name: str,
    **config: Any,
): Series[Any]

All write-back endpoints support the following additional configuration:

Table 3. Parameters:
Name	Optional	Default	Description
`concurrency`	yes	dynamic ^[1]	Concurrency to use for writing back to the DBMS.
`arrowConfiguration`	yes	-	Dict containing additional configuration for the connection from the DBMS to the GDS Arrow Server.
1. Twice the number of processors on the DBMS server

Table 4. Arrow configuration:
Name	Optional	Default	Description
`batchSize`	yes	`10000`	Size of batches retrieved by the DBMS from the session.

4.2. Examples

Extending the previous example, we can write back the FastRP embeddings to the AuraDB instance as follows:

Write mutated FastRP embeddings back to the database:

gds.graph.nodeProperties.write(G, "embedding")

If we want to tune the performance of the write-back, we can configure batchSize and concurrency. In this example we show how to do this with an algorithm .write mode:

Compute WCC and write the component ids back as node properties, with custom concurrency configuration:

gds.wcc.write(
  G,
  writeProperty="wcc",
  concurrency=12,
  arrowConfiguration={"batchSize": 25000}
)

5. Querying the database

You can run Cypher queries on the AuraDB instance using the run_cypher() method. There is no restriction on the type of query that can be run, but it is important to note that the query will be run on the AuraDB instance, and not on the GDS Session. Therefore, you will not be able to call any GDS procedures from the run_cypher() method.

Run a Cypher query to find our written-back embeddings:

gds.run_cypher("MATCH (n:User) RETURN n.name, n.embedding")