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I was working with Apache AGE and I came across a code:

SET search_path = ag_catalog, "$user", public;

Could someone explain what is the meaning of all three parts of the code? Also what other values can these take?

abhishek2046
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10 Answers10

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This is basically used to set the search PATH in Apache Age. The 'search_path' is a variable that determines the order in which database schemas are searched for objects.

'ag_catalog' : Here Apache age store its systems catalogs and metadata.

"$user" : This refer to schema that has name as current user.

 'public':

and this refer default schema in Apache age that accessible to all users.

farrukh raja
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The use of SET search_path here is to set the 'ag_catalog' schema to create objects into the schema by default. The three variables that are assigned are all schemas that are ordered based on the precedence determined by the user.

ag_catalog is a schema with AGE system catalogs, "$user" is the schema of the same name as the current user, and public is the default public schema.

Also whenever objects are referenced, the search path is traversed until the matching object is found.

Ken W.
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There are different schemas or namespaces in PostgreSQL. In each schema there can be numerous tables. Tables are often referred to by unqualified names, which consist of just the table name. The system determines which table is meant by following a search path, which is a list of schemas to look in. The first matching table in the search path is taken to be the one wanted. If there is no match in the search path, an error is reported, even if matching table names exist in other schemas in the database.

    SET search_path = ag_catalog, "$user", public;

The flow of search for a particular search query will be in the order ag_catalog, "$user", public.

Hrishikesh Mallick
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Set the schema for Apache Age with this:

CREATE EXTENSION age;
LOAD 'age';
SET search_path = ag_catalog, "$user", public;

To create a graph, use the create_graph function located in the ag_catalog namespace.

SELECT create_graph('graph_name');

To create a single vertex, use the CREATE clause.

SELECT * FROM cypher('graph_name', $$ CREATE (n) $$) as (v agtype);

for e.g:

SELECT * FROM cypher('mygraph', $$
    CREATE (n:Person {name: 'John Doe', age: 30})
$$) as (v agtype);
MOIEZ IBRAR
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search_path is kind of an environment variable used to store different values for the schemas to be searched.

We can also store values of a particular schema and its attributes like tables, for customized searches.

So modifying search_path allows us to alter search operations to our desires.

Jawad Ali Abbasi
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This is used in PostgreSQL to set the schema search path for the current session.

The schema search path determines the order in which PostgreSQL looks for tables, views, and other database objects when an unqualified object name is referenced in a query.

ag_catalog is a specific schema where Apache AGE stores its metadata, so PostgreSQL will search this schema first when resolving unqualified object names.$user is a special placeholder that refers to the schema named after the current user executing the command. This allows each user to have their own dedicated schema where they can create and manage their objects without interfering with other users.public is the default schema in PostgreSQL where most of the tables and views are typically created if no specific schema is specified.

Chidera Stella Onumajuru
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Without setting the search_path when you need to use age functions like create_graph, drop_graph, cypher and many more, even custom types like agtype you'll have to append the namespace for every query, so in postgres database by default when you run a query and you don't specify the namespace/schema to use it runs the query on the public schema, unless you specify the schema to use like schema_name.object_name then it uses that schema. That's why in the docs you'll see something like ag_catalog.create_graph(), ag_catalog.cypher(). ag_catalog is the schema created in the database when you install the extension. To prevent appending the ag_catalog to any function, custom types etc every time, you'll need to tell postgres the first namespace to look (by default it's public), that's why we SET search_path

Peter
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Set search_path is parameter of PostgreSQL, which is used to control schema search path for a session. The schema search path determines the order in which PostgreSQL looks for objects (tables, functions, etc.)

You can read further by this official Document-1 and Document-2.

Pawan Kukreja
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The system determines which table is meant by following a search path, which is a list of schemas to look in.

To show the current search path, use the following command:

SHOW search_path;

In the default setup this returns:

search_path
--------------
 "$user", public

This is the general/default path of search_path but, you can explicitly define the intended path to get desired results.

Vinay-Agens
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The code sets the schema search path for the current session in PostgreSQL. The search path specifies the order in which PostgreSQL looks for tables and objects in different schemas.

Mahina Sheikh
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