two shared memory segments?

I have a cluster configured for ~800MB of shared memory cache
(shared_buffers = 100000), but ipcs shows TWO shared memory
segments of ~800MB belonging to that postmaster. What kind of
a problem do I have here?

T ID KEY MODE OWNER GROUP CREATOR CGROUP NATTCH SEGSZ CPID LPID ATIME DTIME CTIME
Shared Memory:
m 114695 0x00000000 D-rw------- pg pg pg pg 2 861011968 17065 17065 7:00:07 13:38:22 13:38:22
m 16396 0x0089d911 --rw------- pg pg pg pg 47 861011968 17065 17065 13:38:22 no-entry 13:38:22

The "D" in the MODE for the first one means "the associated
shared memory segment has been removed. It will disappear
when the last process attached to the segment detaches it."
(from 'man ipcs')

However, ipcs says pid 17065 (the live postmaster pid)
created them both. The postmaster has been running for
about 130 days, but the ATIME/DTIME/CTIME columns seem to
suggest both segments are still being accessed.

Ed