How to use dbms_application_info to create session details

The package dbms_application_info lets you add supplemental information in your session, which can be picked up in the V$SESSION view.

A very useful package, which I have used many times myself, but for some reason it is rarely used by Developers. It should typically be called before beginning a transaction in order to register and name a transaction/client_info/module for later use when measuring performance across an application.

exec dbms_application_info.set_client_info('Step one.');
exec dbms_application_info.set_module('module1','gettrades');

Here is an example where I was troubleshooting a "hanging" delete statement for a customer.
Turned out the problem was concurrency locks:

select SID,SERIAL#,SQL_ID,STATUS,osuser,machine,schemaname,MODULE,ACTION,CLIENT_INFO,LOGON_TIME,EVENT,STATE,FINAL_BLOCKING_SESSION "blocking"
from v$session 
WHERE schemaname='SALES'
AND STATUS='ACTIVE'
UNION
select SID,SERIAL#,SQL_ID,STATUS,osuser,machine,schemaname,MODULE,ACTION,CLIENT_INFO,LOGON_TIME,EVENT,STATE,FINAL_BLOCKING_SESSION "blocking"
from v$session 
where SID = (SELECT FINAL_BLOCKING_SESSION FROM V$SESSION WHERE schemaname='SALES' AND STATUS='ACTIVE');

In the resulting two rows, the first one is mine, the second is the blocking session:

SID	SERIAL#	SQL_ID	STATUS	OSUSER	MACHINE	SCHEMANAME	MODULE	ACTION	CLIENT_INFO	LOGON_TIME	EVENT	STATE	blocking
32	4759	5jg1839cyxzgh	ACTIVE	oracle	mytestserver.com	SALES	DELETE MODULE	DELETE_SCHEMA	Delete XSD.	15.02.2018 12:04:43	library cache lock	WAITING	2285
2285	48625	g3bc37vx8fy3u	INACTIVE	JIM	COMPANY\PC-157	SALES	SQL*Plus			14.02.2018 14:08:57	SQL*Net message from client	WAITING	NULL

For more information, check the documentation
Tracing Enhancements Using DBMS_MONITOR (In 10g, 11g and Above) (Doc ID 293661.1) at My Oracle Support.