Row-S lock on child while inserting into parent table

Dear all,

Recently we have discovered that INSERTs into one our dimension table (parent) take definitely too long because of scanning don on each fact table (child) - Row-S locks on children have been noticed.

I was able to reproduce this on very simple example, structure below:

CREATE TABLE parent_tab (

ID NUMBER,

NAME VARCHAR2(20)

);

ALTER TABLE parent_tab ADD CONSTRAINT parent_tab_pk PRIMARY KEY (ID);

CREATE TABLE child_tab (

ID NUMBER,

parent_id NUMBER NOT NULL

);

ALTER TABLE child_tab ADD CONSTRAINT child_tab_pk PRIMARY KEY (ID);

ALTER TABLE child_tab ADD CONSTRAINT child_parent_fk FOREIGN KEY (parent_id) REFERENCES parent_tab(ID);