Say we are using Synaptic Package Manager with our distribution, but the Quick Filter is missing from it. We need to run:
apt-get install apt-xapian-index
and start Synaptic to check it out.
If it still does not appear, we need to close Synaptic and run further:
update-apt-xapian-index -vf
and wait for it to finish.
Starting Synaptic again, we should have Quick Filter available on the toolbar.