The pg_variables module provides functions to work with variables of various types. Created variables live only in the current user session.

Note that the module does not support transactions and savepoints. For example:

SELECT pgv_set('vars', 'int1', 101);
BEGIN;
SELECT pgv_set('vars', 'int2', 102);
ROLLBACK;

SELECT * FROM pgv_list() order by package, name;
 package | name
---------+------
 vars    | int1
 vars    | int2
(2 rows)

This module available under the same license as PostgreSQL.

Typical installation procedure may look like this:

$ cd pg_variables
$ make USE_PGXS=1
$ sudo make USE_PGXS=1 install
$ make USE_PGXS=1 installcheck
$ psql DB -c "CREATE EXTENSION pg_variables;"

The functions provided by the pg_variables module are shown in the tables below. The module supports the following scalar and record types.

To use pgv_get() function required package and variable must exists. It is necessary to set variable with pgv_set() function to use pgv_get() function.

If a package does not exists you will get the following error:

SELECT pgv_get('vars', 'int1', NULL::int);
ERROR:  unrecognized package "vars"

If a variable does not exists you will get the following error:

SELECT pgv_get('vars', 'int1', NULL::int);
ERROR:  unrecognized variable "int1"

pgv_get() function check the variable type. If the variable type does not match with the function type the error will be raised:

SELECT pgv_get('vars', 'int1', NULL::text);
ERROR:  variable "int1" requires "integer" value

The following functions are provided by the module to work with collections of record types.

To use pgv_update(), pgv_delete() and pgv_select() functions required package and variable must exists. Otherwise the error will be raised. It is necessary to set variable with pgv_insert() function to use these functions.

pgv_update(), pgv_delete() and pgv_select() functions check the variable type. If the variable type does not record type the error will be raised.

Note that pgv_stats() works only with the PostgreSQL 9.6 and newer.

It is easy to use functions to work with scalar variables:

SELECT pgv_set('vars', 'int1', 101);
SELECT pgv_set('vars', 'int2', 102);

SELECT pgv_get('vars', 'int1', NULL::int);
 pgv_get_int 
-------------
         101
(1 row)

SELECT pgv_get('vars', 'int2', NULL::int);
 pgv_get_int 
-------------
         102
(1 row)

Let's assume we have a tab table:

CREATE TABLE tab (id int, t varchar);
INSERT INTO tab VALUES (0, 'str00'), (1, 'str11');

Then you can use functions to work with record variables:

SELECT pgv_insert('vars', 'r1', tab) FROM tab;

SELECT pgv_select('vars', 'r1');
 pgv_select
------------
 (1,str11)
 (0,str00)
(2 rows)

SELECT pgv_select('vars', 'r1', 1);
 pgv_select
------------
 (1,str11)
(1 row)

SELECT pgv_select('vars', 'r1', 0);
 pgv_select
------------
 (0,str00)
(1 row)

SELECT pgv_select('vars', 'r1', ARRAY[1, 0]);
 pgv_select
------------
 (1,str11)
 (0,str00)
(2 rows)

SELECT pgv_delete('vars', 'r1', 1);

SELECT pgv_select('vars', 'r1');
 pgv_select
------------
 (0,str00)
(1 row)

You can list packages and variables:

SELECT * FROM pgv_list() order by package, name;
 package | name 
---------+------
 vars    | int1
 vars    | int2
 vars    | r1
(3 rows)

And get used memory in bytes:

SELECT * FROM pgv_stats() order by package;
 package | used_memory
---------+-------------
 vars    |       16736
(1 row)

You can delete variables or hole packages:

SELECT pgv_remove('vars', 'int1');
SELECT pgv_remove('vars');

You can delete all packages and variables:

SELECT pgv_free();