Oracle, limit the row number per user - oracle

Question

I need to limit the number of rows that a query can return for a specific user. I know that I can limit in the SQL query, but I need to avoid that a specific user can build a query that return a huge amount of rows. for this reason I need to limit in the configuration.
Does anybody know if it is possible?

Answer 1

If you have Enterprise Edition you can implement VPD rule using DBMS_RLS package:
SQL> create or replace package pac1
2 is
3 function limit_rows(owner varchar2, tab varchar2) return varchar2;
4 end;
5 /
Package created.
SQL> create or replace package body pac1
2 is
3 function limit_rows(owner varchar2, tab varchar2) return varchar2
4 is
5 begin
6 return ' rownum <= 3';
7 end;
8 end pac1;
9 /
Package body created.
SQL> begin
2 dbms_rls.add_policy('HR','EMPLOYEES','RULE1','HR','PAC1.LIMIT_ROWS','SELECT');
3 end;
4 /
PL/SQL procedure successfully completed.
SQL> select first_name, last_name from hr.employees;
FIRST_NAME LAST_NAME
-------------------- -------------------------
Ellen Abel
Sundar Ande
Mozhe Atkinson
SQL>

Answer 2

You can achieve this with cursors. See example:
SQL> create or replace function exec_query(sql_text varchar2) return sys_refcursor
2 is
3 num_rows number := 3;
4 c1 sys_refcursor;
5 begin
6 open c1 for 'with test as (' || sql_text || ') select * from test where rownum <=' || num_rows ;
7 return c1;
8 end;
9 /
Function created.
SQL> variable c1 refcursor;
SQL> exec :c1 := exec_query('select last_name, salary from hr.employees');
PL/SQL procedure successfully completed.
SQL> print :c1;
LAST_NAME SALARY
------------------------- ----------
King 24000
Kochhar 17000
De Haan 17000

Answer 3

Amount of data is not necessarily equal to amount of load. A single row query can kill a database if it's complex enough.
Answer to this is really complex.
You can take the SQL and create a SQL PLAN from it, and from that data limit from estimated cost and/or estimated rows.
How To Create and Evolve a SQL Plan Baseline
How do I display and read the execution plans for a SQL statement
Example:
I'll create a temp table:
create table tmp_table2 as
select * from user_objects;
then I use Oracle's plan estimation with out actually running the query
declare
l_sql varchar2 (32767);
begin
delete from plan_table;
l_sql := 'select * from tmp_table2';
execute immediate 'explain plan for ' || l_sql;
for i in (select cardinality,
cost,
bytes,
cpu_cost
from PLAN_TABLE
where operation = 'SELECT STATEMENT') loop
if i.cardinality /* rows */
> 500 then
dbms_output.put_line ('Too many rows');
elsif i.cpu_cost > 500000 then
dbms_output.put_line ('Too much CPU');
else
dbms_output.put_line ('About right');
end if;
end loop;
end;
Result;
==>
PL/SQL block executed
Too many rows
Or you can use the Resource manager to limit per session:
Using the Database Resource Manager