Oracle update throws timeout - oracle

Question

I am having a very simple oracle update:
update inv_li_pck_inst set mig_li_pck_inst_id = 9377 where id = 9384
Both records exist in the table inv_li_pck_inst: id=9377 and id=9384
Record with id=9377 is migration record.
Problem is that this very simple update query takes ages to run - and at the end throws timeout exception. What could possibly be wrong here? IDs in the table inv_li_pck_inst are unique.
Table DDL:
CREATE TABLE "TESTING_INV"."INV_LI_PCK_INST"
( "ID" NUMBER NOT NULL ENABLE,
"LI_PCK_ID" NUMBER NOT NULL ENABLE,
"WORKFLOW_ID" NUMBER,
"INSERTED" DATE NOT NULL ENABLE,
"INSERTED_BY" NUMBER(9,0) NOT NULL ENABLE,
"UPDATED" DATE,
"UPDATED_BY" NUMBER(9,0),
"DELETED" DATE,
"DELETED_BY" NUMBER(9,0),
"MIG_LI_PCK_INST_ID" NUMBER,
"STATUS_ID" NUMBER,
"WFI_ID" NUMBER,
"TOF_WFI_ID" NUMBER,
CONSTRAINT "PK_INV_LI_PCK_INST" PRIMARY KEY ("ID")
USING INDEX PCTFREE 10 INITRANS 2 MAXTRANS 255 COMPUTE STATISTICS
STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1
BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT)
TABLESPACE "TESTING_INV_DATA" ENABLE,
CONSTRAINT "FK_LPI_WORKFLOW" FOREIGN KEY ("WORKFLOW_ID")
REFERENCES "TESTING_INV"."WORKFLOW" ("WORKFLOW_ID") ENABLE,
CONSTRAINT "FK_LIPI_STATUS" FOREIGN KEY ("STATUS_ID")
REFERENCES "TESTING_INV"."INV_LI_PCK_INST_STATUS" ("ID") ENABLE,
CONSTRAINT "FK_LIPI_MIG_PCK_INST" FOREIGN KEY ("MIG_LI_PCK_INST_ID")
REFERENCES "TESTING_INV"."INV_LI_PCK_INST" ("ID") ENABLE,
CONSTRAINT "FK_LI_PCK_INST_WFI" FOREIGN KEY ("WFI_ID")
REFERENCES "TESTING_INV"."WFI" ("WFI_ID") ENABLE,
CONSTRAINT "FK_INV_LI_PCK_INST5" FOREIGN KEY ("TOF_WFI_ID")
REFERENCES "TESTING_INV"."WFI" ("WFI_ID") ENABLE,
CONSTRAINT "FK_LPI_LI_PCK" FOREIGN KEY ("LI_PCK_ID")
REFERENCES "TESTING_INV"."INV_LI_PCK" ("ID") ENABLE
) SEGMENT CREATION IMMEDIATE
PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255
NOCOMPRESS LOGGING
STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1
BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT)
TABLESPACE "TESTING_INV_DATA" ;
CREATE INDEX "TESTING_INV"."IDX_LI_PCK_INST_WFI" ON "TESTING_INV"."INV_LI_PCK_INST" ("WFI_ID")
PCTFREE 10 INITRANS 2 MAXTRANS 255 COMPUTE STATISTICS
STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1
BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT)
TABLESPACE "TESTING_INV_DATA" ;
CREATE UNIQUE INDEX "TESTING_INV"."UN_LI_PCK_INST" ON "TESTING_INV"."INV_LI_PCK_INST" (NVL2("DELETED","ID",NULL), "WORKFLOW_ID")
PCTFREE 10 INITRANS 2 MAXTRANS 255 COMPUTE STATISTICS
STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1
BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT)
TABLESPACE "TESTING_INV_DATA" ;
CREATE OR REPLACE EDITIONABLE TRIGGER "TESTING_INV"."TRG_INV_LI_PCK_INST"
before insert on INV_LI_PCK_INST
for each row
begin
select SEQ_INV_LI_PCK_INST.nextval into :new.ID from dual;
end;
/
ALTER TRIGGER "TESTING_INV"."TRG_INV_LI_PCK_INST" ENABLE;

Answer 1

Most probable scenario is that there is an other migration session (or more of them) and it blocks your session.
Simple setup
create table testing
(ID NUMBER primary key,
MIG_ID NUMBER );
alter table testing add (
constraint mig foreign key(MIG_ID) references testing(id));
insert into testing (id, mig_id) values(9384, null);
insert into testing (id, mig_id) values(9377, null);
commit;
If you now performs the UPDATE is goes perfectly smooth:
update testing set mig_id = 9377 where id = 9384;
But if you before the update performs a delete of the migrated ID form an other session and do not commit it, your update will "hang" forever.
-- perform from other session and do not commit
delete from testing where id = 9377;
Why, because if the update would be done and the delete session would be commited - the referential integrity will be violeted. The UPDATE must wait until the deleted is commited or rollbacked to see if the reference ID is there or not.
How to dignose?
Simple check the v$session (or GV of RAC) and see the blocking_status and event
select SID, SERIAL#,STATUS,SQL_ID, BLOCKING_SESSION_STATUS, BLOCKING_SESSION,EVENT
from v$session
where USERNAME = your_user
You will see (most probably) your session with BLOCKING_SESSION_STATUS = VALID and
EVENT = enq: TX - row lock contention. In BLOCKING_SESSION you can find the session ID of your interacting session.
The SQL_ID will tell you what the other session is doing.