How to purge tables from the shared pool

Tables cannot be directly purged from the shared pool using the dbms_shared_pool package. Instead, cursors refering to the table can be purged. To generate statements, use v$sqlarea:

set lines 200
spool purge.sql
set heading off
set feedback off
set verify off
set echo off
set pages 0
set trimspool on

select 'exec DBMS_SHARED_POOL.PURGE (''' || ADDRESS ||','|| HASH_VALUE || ''',''C'');'
from V$SQLAREA 
where SQL_ID IN (SELECT SQL_ID 
                 FROM v$sqlarea 
                 WHERE sql_text like 'SELECT * FROM%SBB.ENTITIY_PR%SYS_P5055%');
select 'exit' from dual;
exit

Execute the file "purge.sql" and the cursors refering to the object "SBB.ENTITY_PR" and the partition "SYS_P5055" will be purged. The Oracle 19c documentation for dbms_shared_pool can be found here

How to purge a cursor from the shared pool using dbms_shared_pool

Find the address and hash value for the particular SQL you're looking for:

select address, hash_value from v$sqlarea where sql_id like 'bjkd7pcyfns86';

ADDRESS	HASH_VALUE
0000000085CD2838	1021993222

Execute the purge procedure:

SQL> exec dbms_shared_pool.purge('0000000085CD2838, 1021993222','C');

Note that the name of the object is the combined values of address and hash value from v$sqlarea.
The value C is what you want to use for cursors.

Note that even if an SQL Plan Baseline is dropped from the SMB, it doesn't mean it won't get used if it is still in the cache.

If you have dropped a plan from your SMB that you would like the optimizer to ignore, you must clear out the cursor that previously using the now dropped SQL Plan baseline from the shared pool using the command above. 

sources:

Oracle Documentation

Login storm against database caused exhausted library cache

One of our databases experienced massive contention in the shared pool, in form of wait events alerted as "library cache locks".

The database was very small indeed, so my natural instinct was to throw some more memory at the virtual host, and rearrange the memory parameters.

This turned out to be a misconception; the resources were sufficient for the instance to work properly.

The problem was caused by an incorrect password configuration on the application server.

What we could observe was:

A totally exhausted shared pool, caused by "library cache lock"

The SQL that seemed to be repeatedly executed was

SELECT /*+ connect_by_filtering */
          privilege#, LEVEL
      FROM sysauth$
CONNECT BY grantee# = PRIOR privilege# AND privilege# > 0
START WITH grantee# = :1 AND privilege# > 0;


SELECT privilege#
  FROM sysauth$
WHERE (grantee# = :1 OR grantee# = 1) AND privilege# > 0;

The V$EVENT_NAME view showed that the wait event was accompanied by the additional information found in the columns parameter1 through parameter3, which turned out to be helpful further on:

select  name, wait_class,parameter1,parameter2,parameter3
from v$event_name
where wait_class = 'Concurrency'
and name = 'library cache lock';

NAME	WAIT_CLASS	PARAMETER1	PARAMETER2	PARAMETER3
library cache lock	Concurrency	handle address	lock address	100*mode+namespace

Further research showed that the problem was due to a built-in delay between failed login attempts in Oracle 11g:

"The 'library cache lock' wait is seen due to the fact that the account status gets updated due to incorrect login.
To prevent password guessing attack, there's a sleep() in the code when incorrect login attempts exceed count of 3.
And because of this sleep() you see a wait on library cache, as the process is yet to release the lock."

In release 11.1.0.7, patch 7715339 was released to remove this delay.

In release 11.2.X, the DBA must set an event to remove the delay, as follows:

alter system set events '28401 trace name context forever, level 1'; 

According to Oracle, the purpose of the built-sleep is to make it harder to succeed in a "password guessing attack", particularly in cases where FAILED_LOGIN_ATTEMPTS is set to UNLIMITED. Oracle Development is pointing out that disabling the sleep-function is not recommended. A better solution is to set the FAILED_LOGIN_ATTEMPTS to a reasonable value.
When the number of failed login attempts for a session hits the limit, the account will be locked. Subsequent logon attempts with incorrect password will then be rejected immediately without any contention in the library cache.

See Bug 15882590 : 'LIBRARY CACHE LOCK' DURING WRONG PASSWORD LOGON ATTEMPTS on My Oracle Support (MOS) for further information.