--
-- test.sql
--
create extension pg_readonly;
--
select unset_cluster_readonly();
 unset_cluster_readonly 
------------------------
 t
(1 row)

select get_cluster_readonly();
 get_cluster_readonly 
----------------------
 f
(1 row)

--
drop table t;
ERROR:  table "t" does not exist
drop function f;
ERROR:  could not find a function named "f"
--
create table t(i int);
create function f(IN p int, OUT i int) returns int as $$
begin
    insert into t(i) values (f.p) returning t.i into f.i;
end$$
language plpgsql;
select set_cluster_readonly();
 set_cluster_readonly 
----------------------
 t
(1 row)

select * from t;
 i 
---
(0 rows)

insert into t values (1);
ERROR:  cannot execute INSERT in a read-only transaction
select f(1);
ERROR:  pg_readonly: cannot execute query containing volatile functions because cluster is read-only
-- However, in this same session, if you call f() before entering in read only mode,
-- it is then able to write during read only mode:
select unset_cluster_readonly();
 unset_cluster_readonly 
------------------------
 t
(1 row)

select f(1);
 f 
---
 1
(1 row)

select set_cluster_readonly();
 set_cluster_readonly 
----------------------
 t
(1 row)

insert into t values (2);
ERROR:  cannot execute INSERT in a read-only transaction
select f(2);
ERROR:  pg_readonly: cannot execute query containing volatile functions because cluster is read-only
select get_cluster_readonly();
 get_cluster_readonly 
----------------------
 t
(1 row)

select f(3);
ERROR:  pg_readonly: cannot execute query containing volatile functions because cluster is read-only
select * from t;
 i 
---
 1
(1 row)

with inserted as (insert into t values(3) returning 3) select * from inserted;
ERROR:  cannot execute SELECT in a read-only transaction
select * from t;
 i 
---
 1
(1 row)

-- DDL is also blocked via ProcessUtility hook
CREATE TABLE t2(i int);
ERROR:  cannot execute CREATE TABLE in a read-only transaction
-- DO block: INSERT inside a DO block should be blocked by the executor hook
DO $$ BEGIN INSERT INTO t VALUES (99); END $$;
ERROR:  cannot execute INSERT in a read-only transaction
CONTEXT:  SQL statement "INSERT INTO t VALUES (99)"
PL/pgSQL function inline_code_block line 1 at SQL statement
select * from t;
 i 
---
 1
(1 row)

-- Large object creation: lo_create() is a SELECT-callable function that
-- writes to the pg_largeobject catalog internally.
SELECT lo_create(0);
ERROR:  pg_readonly: cannot execute query containing volatile functions because cluster is read-only