Table with FK with no Index created will LOCK TABLE during DML ?

Question

Hi all,
Know that always create index for FK on table as FK's value will 99.9% be use in Where query on table.
Had seen info with regards to the above and had not been successfull trying to simulate the  above using:
  DROP TABLE "TABLE2";
  CREATE TABLE "TABLE2"
   (     "A2" VARCHAR2(10 BYTE),
      CONSTRAINT "PK_A2" PRIMARY KEY ("A2") ENABLE
Insert into TABLE2 (A2) values ('AAA');
Insert into TABLE2 (A2) values ('BBB');
Insert into TABLE2 (A2) values ('CCC');
DROP TABLE "TABLE1";
  CREATE TABLE "TABLE1"
   (     "A1" VARCHAR2(10 BYTE),
     "A2" VARCHAR2(10 BYTE),
     "A3" VARCHAR2(10 BYTE),
      CONSTRAINT "PK_A1" PRIMARY KEY ("A1"),
        CONSTRAINT "FK_A1_A2" FOREIGN KEY ("A2")
       REFERENCES "LSD"."TABLE2" ("A2") ENABLE
Insert into TABLE1 (A1,A2,A3) values ('111','AAA','yyy');
Insert into TABLE1 (A1,A2,A3) values ('222','BBB','ZZZ');
  When i UPDATE A3 in TABLE1 using '111' record in SQLPlus without COMMIT,
I was able to UPDATE A3 using '222' in another SQLPlus session, so it does not seems like table is LOCK.
Questions.
1. Am using 10GR2, is the above not applicable to 10G ?
2. Or had understand the above concept wrongly  ?
Thanks In Advance
Zack

Answer 1

Hi Legatti,
I was able to UPDATE A3 using '222' in another SQLPlus session, so it does not seems like table is LOCK.   Thought that when updating more than 1 record in TABLE1 will caused TABLE1 to be LOCK.
Now, try to perform an update on the TABLE1 like below:    SQL>update table1 set A3='aaa' where A1=111;
And open an another session and perform this SQL below    SQL>delete from table2 where A2='BBB'; -- now it's hangs
  Yes !!! Very interesting, it hangs until i do a COMMIT on the UPDATE
and DELETE session shows ORA-02292 Integrity Constraint violated as child record found.
  Now, when i create a index for A2 on TABLE1, it DOES NOT HANG and shows ORA-2292 immediately.
  So, is this the result of having no index for FK column (A2) on TABLE1 and when doing DML ,
before COMMIT, will result in TABLE2 to be hang upon doing DML on TABLE2 ?
Thanks for the valuable lesson learned.
Zack