It is the barrel that is pitted.
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Shoot it, and enjoy it. I have a Remington 1911 manufactured in 1943 that has pitting up and down the barrel. It will put rounds on top of each other at 15 yards.
Pitting isn't ideal, but if it doesn't affect anything, especially in a barrel, not as exposed to elements as the outside of the pistol, I wouldn't loose sleep.
The inside of a pistol barrel is a very violent place, and even with Glock's, whatever finish they are using this week, there can spots that didn't hold the treatment as well.
Glock would possibly replace the barrel if you wanted to pursue the matter with them. The again, they may tell you it's a feature... :)
I would recommend though that with a carry gun, to at least do an inspection once a month even if you don't shoot it. Take it down, use a little oil and swab out the barrel. Preventative maintenance can go a long way. That isn't saying glocks or most any other pistol can't run fine without it, but if the time is available, why not.
TXPO
Call Glock, probably a 90% chance they'll replace the barrel for free.
No need to live with a pitted barrel when a replacement only cost you a bit of time and effort.