On our production servers we have simple function with result_cache, like this:
create or replace function f_rc(p_id number) return number result_cache
is
ret number;
begin
select t.val into ret from rc_table t where t.id=p_id;
return ret;
exception
when no_data_found then
return null;
end;
/
And oracle invalidates its results very frequently without any changes in table or function. I found only 2 cases when oracle invalidates result_cache results without any changes in table:
1. “select for update” from this table with commit; (strictly speaking, select-for-update is DML and it changes blocks, so it’s ok)
2. deleting rows from parent table that has no child records if there is unindexed foreign key with “on delete cascade”.
I test it on 11.2.0.1, 11.2.0.3, on solaris x64 and windows. Test cases for this i will show below.
But none of them can be the cause of our situation: we have no unindexed fk, and even if i lock all rows with “select for update”, it still does not stop invalidating.
In what other cases this happens? Am I right that the oracle does not track any changes, but the captures of the locks and “commits”?
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