Introduction
The following article I am going to let you know more about what is going inside the Apache AGE back-end from the perspective of PostgreSQL and give you a brief introduction about the graph creation on PostgreSQL using Apache AGE.
Prerequisites
- PostgreSQL
- Apache AGE
if you don't have them visit my blogs and you will learn how to install them
The beginning
Mostly everything in Apache AGE is a function that is written in C and being loaded to PostgreSQL as any PL/SQL function
So, create_graph is a function and it is defined on age--1.3.0.sql for example (varies based on version being used)
That how does it look like
CREATE FUNCTION ag_catalog.create_graph(graph_name name)
RETURNS void
LANGUAGE c
AS 'MODULE_PATHNAME';
How it is implemented?
PG_FUNCTION_INFO_V1(create_graph);
/* function that is evoked for creating a graph */
Datum create_graph(PG_FUNCTION_ARGS)
{
char *graph;
Name graph_name;
char *graph_name_str;
Oid nsp_id;
//if no argument is passed with the function, graph name cannot be null
if (PG_ARGISNULL(0))
{
ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("graph name can not be NULL")));
}
//gets graph name as function argument
graph_name = PG_GETARG_NAME(0);
graph_name_str = NameStr(*graph_name);
//checking if the name of the graph falls under the pre-decided graph naming conventions(regex)
if (!is_valid_graph_name(graph_name_str))
{
ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("graph name is invalid")));
}
//graph name must be unique, a graph with the same name should not exist
if (graph_exists(graph_name_str))
{
ereport(ERROR,
(errcode(ERRCODE_UNDEFINED_SCHEMA),
errmsg("graph \"%s\" already exists", graph_name_str)));
}
nsp_id = create_schema_for_graph(graph_name);
//inserts the graph info into the relation which has all the other existing graphs info
insert_graph(graph_name, nsp_id);
//Increment the Command counter before create the generic labels.
CommandCounterIncrement();
//Create the default label tables
graph = graph_name->data;
create_label(graph, AG_DEFAULT_LABEL_VERTEX, LABEL_TYPE_VERTEX, NIL);
create_label(graph, AG_DEFAULT_LABEL_EDGE, LABEL_TYPE_EDGE, NIL);
ereport(NOTICE,
(errmsg("graph \"%s\" has been created", NameStr(*graph_name))));
//according to postgres specification of c-language functions if function returns void this is the syntax
PG_RETURN_VOID();
}
What are the most interesting parts
- Creating a namespace (schema) for that graph
/*
* This is the same with running the following SQL statement.
*
* CREATE SCHEMA `graph_name`
* CREATE SEQUENCE `LABEL_ID_SEQ_NAME`
* AS integer
* MAXVALUE `LABEL_ID_MAX`
* CYCLE
* The sequence will be used to assign a unique id to a label in the graph.
*
* schemaname doesn't have to be graph_name but the same name is used so
* that users can find the backed schema for a graph only by its name.
*
* ProcessUtilityContext of this command is PROCESS_UTILITY_SUBCOMMAND
* so the event trigger will not be fired.
*/
nsp_id = create_schema_for_graph(graph_name);
- Creates new entry on the ag_catalog at the graphs table
// INSERT INTO ag_catalog.ag_graph VALUES (graph_name, nsp_id)
// =
insert_graph(graph_name, nsp_id);
- The following statements creates a table for holding the labels of (vertex and edges)
graph = graph_name->data;
create_label(graph, AG_DEFAULT_LABEL_VERTEX, LABEL_TYPE_VERTEX, NIL);
create_label(graph, AG_DEFAULT_LABEL_EDGE, LABEL_TYPE_EDGE, NIL);
Conclusion
- Create namespace (schema)
- Insert into ag_catalog graphs table a new entry for it
- Create Vertex labels table inside the create namespace
- Create Edge labels table inside the create namespace
See you in next AGE statement under the hood
Resources and References
- AGE GitHub: https://github.com/apache/age
- AGE Website: https://age.apache.org/
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