pg_logical/snapshots directory

Hi All,

While trying to track down my logical decoding problem, I noticed that
my pg_logical/snapshots directory has ~5000 .snap files and is growing at a
rate of about 4 files a minute. The earliest file is from yesterday
afternoon, dating to the time I took our site down and added a column to a
large table.

I have not been able to find any docs on this directory. Can someone point
me to an explanation of this directory and how to manage the number of
.snap files in it (and/or whether I should be worried about the number of
files in it)?

Thanks,
Mark