Postgres - Finding an open cursor and closing it - postgresql

Question

In SQL Server I used following SQL to find an open cursor and closing it in a 'catch' block.
IF EXISTS(SELECT 1 FROM sys.dm_exec_cursors(##SPID) WHERE [name] = 'Crsr_IDs' AND IS_OPEN = 1)
BEGIN
CLOSE Crsr_IDs
DEALLOCATE Crsr_IDs
END
In similar way how to find an open cursor in Postgres with specific name in EXCEPTION block and close it?

Answer 1

You can use pg_cursors table with list of opened cursors:
IF EXISTS(SELECT * FROM pg_cursors WHERE name = 'Crsr_IDs) THEN
CLOSE Crsr_IDs;
END IF;
But usually it is not necessary - if cursor was opened in protected block - BEGIN EXCEPTION WHEN END, then handler of exception closes opened cursors automatically.

Answer 2

You can use the pg_cursors catalog to query for open cursors in your session, but be aware that some of the cursors might have been opened by the system.
Usually you use CLOSE ALL to close all open cursors.

Answer 3

Here I assume that PL/pgSQL is used, and a cursor is assigned to a variable.
If you need to close a cursor if it is open, you can just execute CLOSE (see Using Cursors), and catch exceptions which can happen. For example:
do $$
declare
Crsr_IDs refcursor = 'Crsr_IDs';
begin
begin
close Crsr_IDs;
exception
when invalid_cursor_name or null_value_not_allowed then null;
end;
end;
$$;
Explanations:
CLOSE can raise exceptions in some conditions which we expect to happen.
Possible conditions:
invalid_cursor_name - there is no open cursor with the assigned name. Either the cursor is already closed, or it was not open at all.
null_value_not_allowed - the cursor variable is null. It could be not initialized at all, and the cursor name was not assigned to it.
See PostgreSQL Error Codes.
See Trapping Errors.