Gremlin standards compliance in Amazon Neptune

The following sections provide an overview of the Neptune implementation of Gremlin and how it differs from the Apache TinkerPop implementation.

Neptune implements some Gremlin steps natively in its engine, and uses the Apache TinkerPop Gremlin implementation to process others (see Native Gremlin step support in Amazon Neptune). The following sections provide an overview of cases where Neptune's implementation differs from the TinkerPop implementation.

Applicable Standards for Gremlin

• The Gremlin language is defined by Apache TinkerPop Documentation and the Apache TinkerPop implementation of Gremlin rather than by a formal specification.

• For numeric formats, Gremlin follows the IEEE 754 standard (IEEE 754-2019 - IEEE Standard for Floating-Point Arithmetic. For more information, also see the Wikipedia IEEE 754 page).

Neptune Gremlin Implementation Differences

There are a few important differences between the Amazon Neptune implementation of Gremlin and the implementation defined by Apache TinkerPop.

Note

For some concrete examples of these implementation differences shown in Gremlin Console and Amazon Neptune, see the Using Gremlin to access the graph in Amazon Neptune section of the Quick Start.

The following is a list of implementation differences:

Topics

• Pre-Bound Variables
• TinkerPop Enumerations
• Java Code
• Script Execution
• Sessions
• Transactions
• Vertex and Edge IDs
• User-Supplied IDs
• Vertex Property IDs
• Cardinality of Vertex Properties
• Updating a Vertex Property
• Labels
• Variables
• Escape Characters
• Groovy Limitations
• Serialization
• Lambda Steps
• Unsupported Gremlin Methods
• Unsupported Gremlin Steps
• Other Features
• Gremlin Graph Supported Features

Pre-Bound Variables

The traversal object g is Pre-bound. The graph object is not supported.

TinkerPop Enumerations

Neptune does not support fully qualified class names for enumeration values. For example, you must use single and not org.apache.tinkerpop.gremlin.structure.VertexProperty.Cardinality.single in your Groovy request.

The enumeration type is determined by parameter type.

The following table shows the allowed enumeration values and the related TinkerPop fully qualified name.

Allowed Values	Class
id, key, label, value	org.apache.tinkerpop.gremlin.structure.T
T.id, T.key, T.label, T.value	org.apache.tinkerpop.gremlin.structure.T
set, single	org.apache.tinkerpop.gremlin.structure.VertexProperty.Cardinality
asc, desc, shuffle	org.apache.tinkerpop.gremlin.process.traversal.Order
Order.asc, Order.desc, Order.shuffle	org.apache.tinkerpop.gremlin.process.traversal.Order
global, local	org.apache.tinkerpop.gremlin.process.traversal.Scope
Scope.global, Scope.local	org.apache.tinkerpop.gremlin.process.traversal.Scope
all, first, last, mixed	org.apache.tinkerpop.gremlin.process.traversal.Pop
normSack	org.apache.tinkerpop.gremlin.process.traversal.SackFunctions.Barrier
addAll, and, assign, div, max, min, minus, mult, or, sum, sumLong	org.apache.tinkerpop.gremlin.process.traversal.Operator
keys, values	org.apache.tinkerpop.gremlin.structure.Column
BOTH, IN, OUT	org.apache.tinkerpop.gremlin.structure.Direction
any, none	org.apache.tinkerpop.gremlin.process.traversal.step.TraversalOptionParent.Pick

Java Code

Neptune does not support calls to methods defined by arbitrary Java or Java library calls other than supported Gremlin APIs. For example, java.lang.*, Date(), and g.V().tryNext().orElseGet() are not allowed.

Script Execution

All queries must begin with g, the traversal object.

In String query submissions, multiple traversals can be issued separated by a semicolon (;) or a newline character (\n). To be executed, every statement other than the last must end with an .iterate() step. Only the final traversal data is returned. Note that this does not apply to GLV ByteCode query submissions.

Sessions

Sessions in Neptune are limited to only 10 minutes in duration. See Gremlin script-based sessions and the TinkerPop Session Reference for more information.

Transactions

Neptune opens a new transaction at the beginning of each Gremlin traversal and closes the transaction upon the successful completion of the traversal. The transaction is rolled back when there is an error.

Multiple statements separated by a semicolon (;) or a newline character (\n) are included in a single transaction. Every statement other than the last must end with a next() step to be executed. Only the final traversal data is returned.

Manual transaction logic using tx.commit() and tx.rollback() is not supported.

Important

This only applies to methods where you send the Gremlin query as a text string (see Gremlin transactions).

Vertex and Edge IDs

Neptune Gremlin Vertex and Edge IDs must be of type String. If you don't supply an ID when you add a vertex or an edge, a UUID is generated and converted to a string; for example, "48af8178-50ce-971a-fc41-8c9a954cea62". These ID strings support Unicode characters, and cannot exceed 55 MB in size.

Note

This means that user-supplied IDs are supported, but they are optional in normal usage. However, the Neptune Load command requires that all IDs be specified using the ~id field in the Neptune CSV format.

User-Supplied IDs

User-supplied IDs are allowed in Neptune Gremlin with the following stipulations.

• Supplied IDs are optional.

• Only vertexes and edges are supported.

• Only type String is supported.

To create a new vertex with a custom ID, use the property step with the id keyword: g.addV().property(id, 'customid').

Note

Do not put quotation marks around the id keyword. It refers to T.id.

All vertex IDs must be unique, and all edge IDs must be unique. However, Neptune does allow a vertex and an edge to have the same ID.

If you try to create a new vertex using the g.addV() and a vertex with that ID already exists, the operation fails. The exception to this is if you specify a new label for the vertex, the operation succeeds but adds the new label and any additional properties specified to the existing vertex. Nothing is overwritten. A new vertex is not created. The vertex ID does not change and remains unique.

For example, the following Gremlin Console commands succeed:

gremlin> g.addV('label1').property(id, 'customid')
gremlin> g.addV('label2').property(id, 'customid')
gremlin> g.V('customid').label()
  ==>label1::label2

Vertex Property IDs

Vertex property IDs are generated automatically and can show up as positive or negative numbers when queried.

Cardinality of Vertex Properties

Neptune supports set cardinality and single cardinality. If it isn't specified, set cardinality is selected. This means that if you set a property value, it adds a new value to the property, but only if it doesn't already appear in the set of values. This is the Gremlin enumeration value of Set.

List is not supported. For more information about property cardinality, see the Vertex topic in the Gremlin JavaDoc.

Updating a Vertex Property

To update a property value without adding an additional value to the set of values, specify single cardinality in the property step.

g.V('exampleid01').property(single, 'age', 25)

This removes all existing values for the property.

Labels

Neptune supports multiple labels for a vertex. When you create a label, you can specify multiple labels by separating them with ::. For example, g.addV("Label1::Label2::Label3") adds a vertex with three different labels. The hasLabel step matches this vertex with any of those three labels: hasLabel("Label1"), hasLabel("Label2"), and hasLabel("Label3").

Important

The :: delimiter is reserved for this use only. You cannot specify multiple labels in the hasLabel step. For example, hasLabel("Label1::Label2") does not match anything.

Variables

Neptune does not support Gremlin variables and does not support the bindings property.

Escape Characters

Neptune resolves all escape characters as described in the Escaping Special Characters section of the Apache Groovy language documentation.

Groovy Limitations

Neptune doesn't support Groovy commands that don't start with g. This includes math (for example, 1+1), system calls (for example, System.nanoTime()), and variable definitions (for example, 1+1).

Important

Neptune does not support fully qualified class names. For example, you must use single and not org.apache.tinkerpop.gremlin.structure.VertexProperty.Cardinality.single in your Groovy request.

Serialization

Neptune supports the following serializations based on the requested MIME type.

MIME type	Serialization	Configuration
application/vnd.gremlin-v1.0+gryo	GryoMessageSerializerV1d0	ioRegistries: [org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerIoRegistryV1d0]
application/vnd.gremlin-v1.0+gryo-stringd	GryoMessageSerializerV1d0	serializeResultToString: true}
application/vnd.gremlin-v3.0+gryo	GryoMessageSerializerV3d0	ioRegistries: [org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerIoRegistryV3d0]
application/vnd.gremlin-v3.0+gryo-stringd	GryoMessageSerializerV3d0	serializeResultToString: true
application/vnd.gremlin-v1.0+json	GraphSONMessageSerializerGremlinV1d0	ioRegistries: [org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerIoRegistryV1d0]
application/vnd.gremlin-v2.0+json	GraphSONMessageSerializerV2d0   (only works with WebSockets)	ioRegistries: [org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerIoRegistryV2d0]
application/vnd.gremlin-v3.0+json	GraphSONMessageSerializerV3d0
application/json	GraphSONMessageSerializerV3d0	ioRegistries: [org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerIoRegistryV3d0]
application/vnd.graphbinary-v1.0	GraphBinaryMessageSerializerV1

Lambda Steps

Neptune does not support Lambda Steps.

Unsupported Gremlin Methods

Neptune does not support the following Gremlin methods:

• org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversal.program(org.apache.tinkerpop.gremlin.process.computer.VertexProgram)

• org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversal.sideEffect(java.util.function.Consumer)

• org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversal.from(org.apache.tinkerpop.gremlin.structure.Vertex)

• org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversal.to(org.apache.tinkerpop.gremlin.structure.Vertex)

For example, the following traversal is not allowed: g.V().addE('something').from(__.V().next()).to(__.V().next()).

Important

This only applies to methods where you send the Gremlin query as a text string.

Unsupported Gremlin Steps

Neptune does not support the following Gremlin steps:

• The Gremlin io( ) Step is only partially supported in Neptune. It can be used in a read context, as in g.io((url)).read(), but not to write.

Other Features

The Neptune implementation of Gremlin does not expose the graph object. The following section describes the supported and unsupported graph features.

Gremlin Graph Supported Features

The following is a set of features as implemented by the Neptune Gremlin graph. These features are the same as would be returned by the graph.features() command.

Graph Feature	Enabled
Transactions	true
ThreadedTransactions	false
Computer	false
Persistence	true
ConcurrentAccess	true

Variable Feature	Enabled
Variables	false
SerializableValues	false
UniformListValues	false
BooleanArrayValues	false
DoubleArrayValues	false
IntegerArrayValues	false
StringArrayValues	false
BooleanValues	false
ByteValues	false
DoubleValues	false
FloatValues	false
IntegerValues	false
LongValues	false
MapValues	false
MixedListValues	false
StringValues	false
ByteArrayValues	false
FloatArrayValues	false
LongArrayValues	false

Vertex Feature	Enabled
MetaProperties	false
DuplicateMultiProperties	false
AddVertices	true
RemoveVertices	true
MultiProperties	true
UserSuppliedIds	true
AddProperty	true
RemoveProperty	true
NumericIds	false
StringIds	true
UuidIds	false
CustomIds	false
AnyIds	false

Vertex Property Feature	Enabled
UserSuppliedIds	false
AddProperty	true
RemoveProperty	true
NumericIds	true
StringIds	true
UuidIds	false
CustomIds	false
AnyIds	false
Properties	true
SerializableValues	false
UniformListValues	false
BooleanArrayValues	false
DoubleArrayValues	false
IntegerArrayValues	false
StringArrayValues	false
BooleanValues	true
ByteValues	true
DoubleValues	true
FloatValues	true
IntegerValues	true
LongValues	true
MapValues	false
MixedListValues	false
StringValues	true
ByteArrayValues	false
FloatArrayValues	false
LongArrayValues	false

Edge Feature	Enabled
AddEdges	true
RemoveEdges	true
UserSuppliedIds	true
AddProperty	true
RemoveProperty	true
NumericIds	false
StringIds	true
UuidIds	false
CustomIds	false
AnyIds	false

Edge Property Feature	Enabled
Properties	true
SerializableValues	false
UniformListValues	false
BooleanArrayValues	false
DoubleArrayValues	false
IntegerArrayValues	false
StringArrayValues	false
BooleanValues	true
ByteValues	true
DoubleValues	true
FloatValues	true
IntegerValues	true
LongValues	true
MapValues	false
MixedListValues	false
StringValues	true
ByteArrayValues	false
FloatArrayValues	false
LongArrayValues	false