I am running in the situation where lag on extract process is in increasing mode.

Observation : Lag in integrated extract process is in increasing mode.

I tried restarting the extract process but even after restarting lag is in increasing mode.

Then I have restarted the oracle database and after that lag got cleared.

Question :
1. What are the possible reason for increasing in extract lag.
2. What things I should check at that time.
3. I can see that after restarting the DB lag got removed, Seems some contention in database and after restart of DB lag got removed, what are the possible contention for the same.