在apache时代的create_graph的引擎盖下
#教程 #database #apacheage #graphdatabas

介绍

以下文章，我将从PostgreSQL的角度让您更多地了解Apache Age Age后端的情况，并为您提供有关使用Apache Age在Postgresql上的图形创建的简短介绍。


under-the-hood

让我们

先决条件

  • PostgreSQL
  • Apache Age

如果您没有他们访问我的博客，您将学习如何安装它们

开始

主要是Apache Age中的所有内容都是用C编写并加载到PostgreSQL的函数，作为任何PL/SQL函数

so， create_graph 是一个函数，它在age-1.3.0.sql中定义（例如，根据使用的版本而变化）

看起来如何

CREATE FUNCTION ag_catalog.create_graph(graph_name name)
RETURNS void
LANGUAGE c
AS 'MODULE_PATHNAME';

如何实施？


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(); 
}

最有趣的部分是什么

  • 为该图创建一个名称空间（架构） 
    /*
     * 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);
  • 在图表上的AG_CATALOG上创建新条目 
// INSERT INTO ag_catalog.ag_graph VALUES (graph_name, nsp_id)
// = 
    insert_graph(graph_name, nsp_id);
  • 以下语句创建了一个表格，用于保留（顶点和边缘）的标签 
    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);

结论

  • 创建名称空间（schema）
  • 插入ag_catalog图表表
  • 在创建名称空间内创建顶点标签表
  • 创建边缘标签表格中的“创建名称空间”

在引擎盖下的下一个年龄陈述中与您见面

资源和参考