pg_variables - session variables with various types

Introduction

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

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

License

This module available under the same license as PostgreSQL.

Installation

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;"

Module functions

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_() functions required package and variable must exists. It is necessary to set variable with pgv_set_() functions to use pgv_get_() functions.

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

SELECT pgv_get_int('vars', 'int1');
ERROR:  unrecognized package "vars"

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

SELECT pgv_get_int('vars', 'int1');
ERROR:  unrecognized variable "int1"

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

SELECT pgv_get_text('vars', 'int1');
ERROR:  variable "int1" requires "integer" value

Integer variables

Function	Returns
pgv_set_int(package text, name text, value int)	void
pgv_get_int(package text, name text, strict bool default true)	int

Text variables

Function	Returns
pgv_set_text(package text, name text, value text)	void
pgv_get_text(package text, name text, strict bool default true)	text

Numeric variables

Function	Returns
pgv_set_numeric(package text, name text, value numeric)	void
pgv_get_numeric(package text, name text, strict bool default true)	numeric

Timestamp variables

Function	Returns
pgv_set_timestamp(package text, name text, value timestamp)	void
pgv_get_timestamp(package text, name text, strict bool default true)	timestamp

Timestamp with timezone variables

Function	Returns
pgv_set_timestamptz(package text, name text, value timestamptz)	void
pgv_get_timestamptz(package text, name text, strict bool default true)	timestamptz

Date variables

Function	Returns
pgv_set_date(package text, name text, value date)	void
pgv_get_date(package text, name text, strict bool default true)	date

Jsonb variables

Function	Returns
pgv_set_jsonb(package text, name text, value jsonb)	void
pgv_get_jsonb(package text, name text, strict bool default true)	jsonb

Records

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.

Function	Returns	Description
pgv_insert(package text, name text, r record)	void	Inserts a record to the variable collection. If package and variable do not exists they will be created. The first column of r will be a primary key. If exists a record with the same primary key the error will be raised. If this variable collection has other structure the error will be raised.
pgv_update(package text, name text, r record)	boolean	Updates a record with the corresponding primary key (the first column of r is a primary key). Returns true if a record was found. If this variable collection has other structure the error will be raised.
pgv_delete(package text, name text, value anynonarray)	boolean	Deletes a record with the corresponding primary key (the first column of r is a primary key). Returns true if a record was found.
pgv_select(package text, name text)	set of record	Returns the variable collection records.
pgv_select(package text, name text, value anynonarray)	record	Returns the record with the corresponding primary key (the first column of r is a primary key).
pgv_select(package text, name text, value anyarray)	set of record	Returns the variable collection records with the corresponding primary keys (the first column of r is a primary key).

Miscellaneous functions

Function	Returns	Description
pgv_exists(package text, name text)	bool	Returns true if package and variable exists.
pgv_exists(package text)	bool	Returns true if package exists.
pgv_remove(package text, name text)	void	Removes the variable with the corresponding name. Required package and variable must exists, otherwise the error will be raised.
pgv_remove(package text)	void	Removes the package and all package variables with the corresponding name. Required package must exists, otherwise the error will be raised.
pgv_free()	void	Removes all packages and variables.
pgv_list()	table(package text, name text)	Returns set of records of assigned packages and variables.
pgv_stats()	table(package text, used_memory bigint)	Returns list of assigned packages and used memory in bytes.

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

Examples

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

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

SELECT pgv_get_int('vars', 'int1');
 pgv_get_int 
-------------
         101
(1 row)

SELECT pgv_get_int('vars', 'int2');
 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();