How to find out past pending transactions - database

Question

I'm looking a way to find out if there are uncommited statements in past sessions.
I have already checked in the current session V$TRANSACTION but there is nothing.
I found out that the first troubleshooting was produced at 2018-06-29 13:35:07.236 using this request:
SELECT * FROM DBA_HIST_ACTIVE_SESS_HISTORY
where
event ='enq: TX - row lock contention' and
sample_time > ({ts '2018-06-29 12:41:09'})
order by sample_time ASC
Is there a way to find out the session id and the user id which used uncommited transactions?
I know how to detect in the current sessions but no in past session.

Answer 1

If I understand what you are trying to do, there is no need to go looking for uncommitted transactions. DBA_HIST_ACTIVE_SESS_HISTORY has a BLOCKING_SESSION column that will tell you what the session was waiting on at that time.
In the case of a session waiting on enq: TX - row lock contention, the blocking session should be the session that was holding the lock (i.e., the session in the middle of the "uncommitted transaction" you were looking for).
To get the details of sessions with their blockers, do something like this:
SELECT s.*, blk.*
FROM dba_hist_active_sess_history s
-- Add this join to get blocking session
INNER JOIN dba_hist_active_sess_history blk
ON blk.session_id = s.blocking_session
AND blk.dbid = s.dbid
AND blk.snap_id = s.snap_id
AND blk.instance_number = s.instance_number
AND blk.sample_id = s.sample_id

Answer 2

When I use your request, I don't find the root cause:
SELECT s.*, blk.*
FROM dba_hist_active_sess_history s
INNER JOIN dba_hist_active_sess_history blk
ON blk.session_id = s.blocking_session
AND blk.dbid = s.dbid
AND blk.snap_id = s.snap_id
AND blk.instance_number = s.instance_number
AND blk.sample_id = s.sample_id
where
s.event ='enq: TX - row lock contention' and
s.sample_time > ({ts '2018-06-29 12:41:09'})
order by s.sample_time ASC
It displays 5781 (2018-06-29 13:37:10.006) as blocking_session. And then with your join, it indicates that session 5781 is blocked by session 1907 (2018-06-29 13:37:10.006).
Do you know how to find the root blocking session id and its SQL_ID because it's required to search in Java code a non-closed transaction that caused this blocking session.