From Catchin’ the Tune by the Irish Tradition.
I’m not sure "jig" is really what I’d call this, more like a fast march. The long rest in the B part is a good time to grab a sip before you have to start playing the tune again.
Dick Gaughan plays this on the album, Coppers and Brass.
This is a lovely jig, fits well on pipes and whistle in this key.
Re: Planxty Johnston
For us whistlers and pipers, the first version above works if you play the first line and the first two bars of line six up an octave. The octave jump actually works smoothly - for me anyway - especially as I play it after John O’Connor.