What is the meaning of "Al Ta'aleni ba'Chatzi Yamai"?
Rashi: Do not remove us to destroy us from the land in the hands of our enemies in the middle of our days.
Radak: Do not cut me off in the middle of my days. This is like "ka'Alos Gadish b'Ito" (Iyov 5:26), "va'Ta'al Shichvas ha'Tal" (Shemos 16:14).
Radak citing Ibn Ezra: This refers to the Neshamah ascending when it separates from the body - "veha'Ru'ach Tashuv El ha'Elokim Asher Nesanah", "ha'Olah Hi l'Ma'alah"(Koheles 12:7, 3:21).
Why does it say "b'Dor Dorim Shenosecha"?
Rashi, Metzudas David: Our days are the years that You allotted to each generation. You promised to sustain us in front of You - "u'Shenocsecha Lo Yitamu; ? v'Zar'am Lefanecha Yikon" (verses 28-29).
Radak: This is like it says above - You dwell forever.