Oracle: Delete statement becomes very slow when using variable - sql

Question

I have an Oracle procedure that normally takes around 5 minutes to run. There are two areas in the procedure where I need to query a list of id numbers that may have been modified. The query in these two segments is identical. The first is at the beginning of a cursor definition, and the second is in a delete statement in the main body of the procedure. The key part that is repeated a lot involves getting the most recent date a certain table was refreshed. The entire procedure is fairly lengthy, so I'll include only the relevant bits below.
Here is the beginning of the cursor:
cursor gvg_profile_c is
with last_refreshed as
(select trunc(max(t.last_refreshed)) as max_date
from ad.pbi_gvg_profile t),
with modified_ids as
(
select distinct id_number
from ad.hr_giving cg
join ad.pbi_dates d
on d.DATE_FULL = trunc(cg.processed_date)
where d.RELATIVE_DATE >= (select max_date from last_refreshed)
and d.RELATIVE_DATE <= trunc(CURRENT_DATE)
and cg.fiscal_year >= ad.current_fiscal_year - 6
union
select distinct gi.gift_donor_id as id_number
from ad.gift gi
where gi.date_added >= (select max_date from last_refreshed)
or gi.date_modified >= (select max_date from last_refreshed)
union
select distinct p.pledge_donor_id as id_number
from ad.pledge_rev p
where p.date_added >= (select max_date from last_refreshed)
or p.date_modified >= (select max_date from last_refreshed)
union
select distinct a.id_number
from ad.affiliation a
where a.date_added >= (select max_date from last_refreshed)
or a.date_modified >= (select max_date from last_refreshed)
),
Here is the delete statment:
delete from ad.pbi_gvg_profile p
where p.id_number in
(with last_refreshed as (select trunc(max(t.last_refreshed)) as max_date
from ad.pbi_gvg_profile t)
select distinct id_number
from ad.hr_giving cg
join ad.pbi_dates d
on d.DATE_FULL = trunc(cg.processed_date)
where d.RELATIVE_DATE >= (select max_date from last_refreshed)
and d.RELATIVE_DATE <= trunc(CURRENT_DATE)
and cg.fiscal_year >= ad.current_fiscal_year - 6
union
select distinct gi.gift_donor_id as id_number
from ad.gift gi
where gi.date_added >= (select max_date from last_refreshed)
or gi.date_modified >= (select max_date from last_refreshed)
union
select distinct p.pledge_donor_id as id_number
from ad.pledge_rev p
where p.date_added >= (select max_date from last_refreshed)
or p.date_modified >= (select max_date from last_refreshed)
union
select distinct a.id_number
from ad.affiliation a
where a.date_added >= (select max_date from last_refreshed)
or a.date_modified >= (select max_date from last_refreshed)
);
I thought it would make more sense and be more efficient to a have a function that calculates the last_refreshed date and puts it in a variable that can be reused. So I did that. Here's the function:
NOTE: You can see here that I sometimes need to get the date from a different table. That is accounted for for the above code via an if/else, I just left it out so you don't have to read identical code 4 times.
function get_last_refreshed_date(scope in smallint) return date is
last_refreshed date;
table_name varchar2(30);
select_sql varchar2(255);
begin
if scope = c_scope_all then
table_name := 'ad.pbi_gvg_profile';
else
table_name := 'ad.pbi_gvg_profile_ag';
end if;
select_sql := 'select trunc(max(last_refreshed))
from '||table_name;
execute immediate select_sql
into last_refreshed;
return(last_refreshed);
end get_last_refreshed_date;
Then I change the beginning of my cursor to use this function and a variable instead, so now it looks like this:
last_refreshed date := get_last_refreshed_date(scope);
cursor gvg_profile_c is
with modified_ids as
(
select distinct id_number
from ad.hr_giving cg
join ad.pbi_dates d
on d.DATE_FULL = trunc(cg.processed_date)
where d.RELATIVE_DATE >= last_refreshed
and d.RELATIVE_DATE <= trunc(CURRENT_DATE)
and cg.fiscal_year >= ad.current_fiscal_year - 6
union
select distinct gi.gift_donor_id as id_number
from ad.gift gi
where gi.date_added >= last_refreshed
or gi.date_modified >= last_refreshed
union
select distinct p.pledge_donor_id as id_number
from ad.pledge_rev p
where p.date_added >= last_refreshed
or p.date_modified >= last_refreshed
union
select distinct a.id_number
from ad.affiliation a
where a.date_added >= last_refreshed
or a.date_modified >= last_refreshed
),
This works fine. My procedure still only takes 5 minutes to run.
However, when I make the same identical change to the Delete statement, suddenly the procedure takes about 65 minutes to run. And I can tell from logging that the execution of the delete statement accounts for over 60 of those minutes.
Why would the variable work fine in the cursor, but cause a major slowdown in a delete statement in the body of the procedure?
Any help is greatly appreciated!