Why Simple Oracle Update Statement Make Block Session? - oracle

Question

I have simple Oracle (19C) update statement like this and it is making block sessions some times. This update query is running from an ASP.NET MVC System which uses Entity Framework. Since I am new to this issue, Can anyone provide me an idea how I can figure out the exact issue, what can be the reason and how can I resolve it?
UPDATE "TICKET_TRACKINGPRD"."TKT_TICKET"
SET
"TITLE" = :b22,
"SUMMARY" = :b21,
"DESCRIPTION" = :b20,
"ENVIRONMENT" = :b19,
"TICKET_PROJECT_ID" = :b18,
"TICKET_PROJECT_MODULE_ID" = NULL,
"APPLICATION_TYPE_ID" = :b17,
"APPLICATION_ID" = :b16,
"APPLICATION_MODULE_ID" = :b15,
"APPLICATION_SERVICE_ID" = :b14,
"SERVICE_CHANNEL_ID" = :b13,
"TICKET_STATUS_ID" = :b12,
"TICKET_RESOLUTION_ID" = :b11,
"TICKET_PRIORITY_ID" = :b10,
"ASSIGNEE_ID" = :b9,
"DUE_DATE" = :b8,
"REPORTED_BY_USER_NAME" = :b7,
"USER_LANGUAGE_ID" = :b6,
"CLOSED_DATE" = NULL,
"CLOSED_BY_USER_ID" = NULL,
"CONTEXT_KEY" = NULL,
"CONTEXT_URL" = NULL,
"CREATED_DATE" = :b5,
"MODIFIED_DATE" = :b4,
"CREATED_BY_USER_ID" = :b3,
"MODIFIED_BY_USER_ID" = :b2,
"RECORD_STATUS_ID" = :b1
WHERE
("ID" = :b23)
RETURNING "KEY" INTO : o0

Answer 1

I'm not saying that this is "it", but ... might be.
what can be the reason
Looks like the unindexed foreign keys issue. Basically, all foreign key columns should be indexed. As documentation says:
Indexing the foreign keys in child tables provides the following benefits:
Prevents a full table lock on the child table. Instead, the database acquires a row lock on the index.
For more info, read Locks and foreign keys.
and how can I resolve it?
Obviously, by indexing foreign key columns. But, first you have to find them. I use Tom Kyte's script (adjusted a little bit):
/* 12.12.2012. Tom Kyte: locating unindexed foreign keys
14.03.2016. PAR_WHAT: 0 - show those that aren't OK
1 - show those that are OK
NULL - show all
*/
WITH forkey
AS (SELECT DECODE (b.table_name, NULL, '****', 'ok') Status,
a.table_name,
a.columns column_1,
b.columns column_2
FROM ( SELECT SUBSTR (a.table_name, 1, 30) table_name,
SUBSTR (a.constraint_name, 1, 30) constraint_name,
MAX (
DECODE (position,
1, SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (position,
2, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (position,
3, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (position,
4, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (position,
5, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (position,
6, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (position,
7, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (position,
8, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (position,
9, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (
position,
10, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (
position,
11, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (
position,
12, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (
position,
13, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (
position,
14, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (
position,
15, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (
position,
16, ', ' || SUBSTR (column_name, 1, 30),
NULL))
columns
FROM user_cons_columns a, user_constraints b
WHERE a.constraint_name = b.constraint_name
AND b.constraint_type = 'R'
GROUP BY SUBSTR (a.table_name, 1, 30),
SUBSTR (a.constraint_name, 1, 30)) a,
( SELECT SUBSTR (table_name, 1, 30) table_name,
SUBSTR (index_name, 1, 30) index_name,
MAX (
DECODE (column_position,
1, SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (column_position,
2, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (column_position,
3, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (column_position,
4, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (column_position,
5, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (column_position,
6, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (column_position,
7, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (column_position,
8, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (column_position,
9, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (
column_position,
10, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (
column_position,
11, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (
column_position,
12, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (
column_position,
13, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (
column_position,
14, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (
column_position,
15, ', ' || SUBSTR (column_name, 1, 30),
NULL))
|| MAX (
DECODE (
column_position,
16, ', ' || SUBSTR (column_name, 1, 30),
NULL))
columns
FROM user_ind_columns
GROUP BY SUBSTR (table_name, 1, 30),
SUBSTR (index_name, 1, 30)) b
WHERE a.table_name = b.table_name(+)
AND b.columns(+) LIKE a.columns || '%'
AND a.table_name NOT LIKE 'HEP_DP%')
SELECT f.status,
f.table_name,
f.column_1,
f.column_2
FROM forkey f
WHERE f.status =
CASE
WHEN :par_what = 1 THEN 'ok'
WHEN :par_what = 0 THEN '****'
ELSE f.status
END
ORDER BY f.table_name, f.column_1, f.column_2
/
For example:
SQL> create table a (id number primary key);
Table created.
SQL> create table b (id number constraint fk_ba references a (id));
Table created.
Table B misses index on its foreign key constraint column, so query returns:
SQL> /
STATUS TABLE_NAME COLUMN_1 COLUMN_2
---------- ---------- ---------- ----------
**** B ID
Create an index:
SQL> create index a1bid on b (id);
Index created.
Query doesn't return anything now:
SQL> /
no rows selected
See if it helps.