This is a descending E Mixolydian [E F# G# A B C# D] run that moves across the strings and eventually down the neck in a cascading type of contour.
It’s based on a recurring nine-note melodic motif of three 16th-note triplets, with three alternate-picked notes followed by two double pull-offs.
I begin in ninth position with a fairly compact shape that spans the ninth to 12th frets. At the end of bar 1 and moving into bar 2, the fret hand shifts down two frets and spreads out to cover a four-fret span, from the seventh fret to the 11th. Use your first, second and fourth fingers to fret the notes.
The fret hand quickly shifts down to a lower position at the beginning of bars 3, 4 and 5, so try to make these transitions as smooth and seamless as possible. Make sure your pull-offs are loud and clear, and use the palm of your pick hand to mute the unused lower strings during bars 1 and 2.
Betcha Can't Play This: John Petrucci's Descending E Mixolydian Run
Source: Guitar World