All the talk about various writings re sessions reminds me of a great book which speaks to this topic, and many others in Irish trad music: Last Night's Fun: In And Out Of Time With Irish Music,
by Ciaran Carson (North Point Press, 1996). I think it's out of print now, but is one of the most enjoyable reads you will ever find on Irish music, culture, camaraderie amongst musicians, by a man who is right in the middle of it all. Find it in your library or perhaps online in a used book place. I have given away more copies of this book than I can count, and am now down to my last, precious signed copy from Ciaran.
Thanks, everyone, for the great reading recommendations on Irish trad sessions,