ORA-28268: Exceeded the maximum allowed size for Context information in a session

Note: Tested in Oracle 19.18.

1. Test Setup

-- code from Blog: "library cache: mutex X" and Application Context 
--    (http://ksun-oracle.blogspot.com/2016/11/library-cache-mutex-x-and-application.html)
create or replace context test_ctx using test_ctx_pkg;

--create or replace context test_ctx using test_ctx_pkg accessed globally;

create or replace package test_ctx_pkg is 
  procedure set_val (attr varchar2, val varchar2);
 end;
/

create or replace package body test_ctx_pkg is
  procedure set_val (attr varchar2, val varchar2) as
  begin
    --dbms_session.clear_all_context('TEST_CTX');
    dbms_session.set_context('TEST_CTX', attr, val);
  end;
end;
/

create or replace procedure ctx_set(p_cnt number, attr_pre varchar2, val_pre varchar2) as
begin
 for i in 1..p_cnt loop
  test_ctx_pkg.set_val(attr_pre||i, val_pre||i);    -- 'library cache: mutex X' on TEST_CTX
 end loop;
end;
/

create or replace procedure test_ORA_28268 (p_cnt number) as 
  l_attr_pre varchar2(32000);
  l_val_pre  varchar2(32000);
  l_val      varchar2(32000);
begin
  --dbms_session.clear_all_context('TEST_CTX');
  ctx_set(p_cnt, 'ATTR_', 'VAL_');
  
  select sys_context('TEST_CTX', 'ATTR_'||1) into l_val from dual;
  dbms_output.put_line('l_attr='||'ATTR_'||1||', VAL='||l_val);
  
  select sys_context('TEST_CTX', 'ATTR_'||p_cnt) into l_val from dual;
  dbms_output.put_line('l_attr='||'ATTR_'||p_cnt||', VAL='||l_val); 
end;
/

create or replace procedure list_context as 
  l_tab  dbms_session.appctxtabtyp;
  l_size number;
begin
  dbms_session.list_context(l_tab, l_size);
  dbms_output.put_line('l_tab.count: '||l_tab.count||', l_size:'||l_size);
  for i in 1..l_tab.count loop
    dbms_output.put_line('namespace: '||l_tab(i).namespace||', attribute: '||l_tab(i).attribute||', value: '||l_tab(i).value);
  end loop;
end;
/

2. Test Run

SQL > exec test_ORA_28268(10000-300);

      l_attr=ATTR_1, VAL=VAL_1
      l_attr=ATTR_9700, VAL=VAL_9700

SQL > exec test_ORA_28268(10000+300);

      BEGIN test_ORA_28268(10000+300); END;
      ERROR at line 1:
      ORA-28268: Exceeded the maximum allowed size for Context information in a session
      ORA-06512: at "SYS.DBMS_SESSION", line 141
      ORA-06512: at "K.TEST_CTX_PKG", line 5
      ORA-06512: at "K.CTX_SET", line 4
      ORA-06512: at "K.TEST_ORA_28268", line 7
      ORA-06512: at line 1

3. ORA-28268

Oracle document:

  28268, 0000, "Exceeded the maximum allowed size for Context information in a session"
  // *Cause:    The maximum size specified by the _session_context_size
  //            init.ora parameter was exceeded.
  // *Action: Please change the value for _session_context_size in the
  //  

ORA-28268 is raised when the number of session local context entries exceeded limit (session local context array) which is defined by "_session_context_size" (default 10,000).

It is only applied to local context (dba_context.type = 'ACCESSED LOCALLY')
(for global context, ORA-04031 when too many global context entries, check v$sgastat.name = 'Global Context').

It's value can be modified by:

  alter system set "_session_context_size"=10000 scope=spfile;

One cause of ORA-28268 is probably session local context leak.

The name "_session_context_size" seems misleading, mabybe renamed as "_session_context_entry_limit".