A classic, upbeat, swing-blues progression, consisting entirely of ninth chords (G9, C9 and D9), which opens up many opportunities for soloing.

The minor pentatonic / Blues scale works well, even though the piece is actually in a major key – which means Mixolydian mode is ideal.

To be technically correct, you need to change key with each chord, playing the mixolydian mode for each of the chords: G mixolydian over the G9, G dorian over the C9 (which shares the same notes a C mixolydian) and G major over the D9 (which shares the same notes as D mixolydian).
Enjoy! :)