Poor performance between schemas

Hello,

DB: 10.2.0.5

OS: HPUX

Some days ago, we had a performance issue in one application stored on the database during 10-20 minutes, the app servers reached the max session pool. It seems to be because the performance on DB

Investigating and asking the app managers, one of them said that she had executed a process on the DB which seems to be not very optimized and User IO consumed much DB time. This process belong to another application. Both apps belongs to the same database, but in different schemas. The number of sessions increased on database from 200 to 285 on that time.