Question

We’ve a preparedStatement which needs to do multiple operations on the db, so all those sql statements are enclosed in a BEGIN-END block like

BEGIN
 DELETE FROM...WHERE A=?..
 UPDATE TABLE...WHERE B=?..
END;

But many reviewers said this will result in a hard parse. From my understanding hard parse is when an sql is not found in the shared pool, then the syntax, execution plan ..everything needs to be calculated again, but here shouldn’t Oracle treat them as individual sql statements.
How can I find out that oracle will do a hard parse or not on a given sql statement?

Answer 1

Bind variables work in PL/SQL blocks just as well as they do in SQL statements.

You can test this by running simple statements in a loop, then look at the parse counts in v$sesstat.

Create a simple table to use for inserting and deleting. Get initial parse counts.

create table test1(a number);

--Flush the pool, or else this test won't be repeatable.
alter system flush shared_pool;

select value, name
from v$sesstat natural join v$statname
where sid = sys_context('userenv', 'sid')
    and name in ('parse count (total)', 'parse count (hard)');

47  parse count (total)
5   parse count (hard)

This is what hard parsing looks like:

begin
    for i in 1 .. 10000 loop
        execute immediate 'insert into test1 values('||i||')';
    end loop;
    commit;
end;
/

select value, name
from v$sesstat natural join v$statname
where sid = sys_context('userenv', 'sid')
    and name in ('parse count (total)', 'parse count (hard)');

10072   parse count (total)
10007   parse count (hard)

PL/SQL blocks with bind variables do not always hard parse. Note that the parse counts are cumulative, and they only increase very slightly here.

begin
    for i in 1 .. 10000 loop
        execute immediate 
        'begin
            delete from test1 where a = :i;
        end;'
        using i;
    end loop;
    commit;
end;
/

select value, name
from v$sesstat natural join v$statname
where sid = sys_context('userenv', 'sid')
    and name in ('parse count (total)', 'parse count (hard)');

10106   parse count (total)
10019   parse count (hard)