ITL - Interested Transaction List

first of all, some lines about theory.

interested transaction list (ITL)

Information in the block header of every segment that determines whether a transaction was uncommitted when the database began modifying the block. Entries in the ITL describe which transactions have rows locked and which rows in the block contain committed and uncommitted changes.

ITL Waits

ITL Waits happens when a session sets a DML transaction and this needs to acquire an ITL slot within data header block but there is not enough space in the pctfree area hence the session has to wait that other DML transaction is commited o rolled back therefore an ITL slot will be avaiable.