log message

I found this in my logs.  What does it mean?

<snip>
DEBUG:  --Relation message--
DEBUG:  Pages 11: Changed 0, reaped 10, Empty 0, New 0; Tup 182: Vac 2,
Keep/VTL 0/0, Crash 0, UnUsed 303, MinLen 100, MaxLen 2380; Re-using:
Free/Avail. Space 53884/2060; EndEmpty/Avail. Pages 6/1. CPU 0.00s/0.00u
sec.
DEBUG:  Index message_pod_key: Pages 2; Tuples 182: Deleted 0. CPU
0.00s/0.00u sec.
DEBUG:  Index message_originator_key: Pages 2; Tuples 182: Deleted 0.
CPU 0.00s/0.00u sec.
DEBUG:  Index message_pkey: Pages 2; Tuples 182: Deleted 0. CPU
0.00s/0.00u sec.
DEBUG:  Rel message: Pages: 11 --> 5; Tuple(s) moved: 0. CPU 0.00s/0.00u
sec.
NOTICE:  FlushRelationBuffers(message, 5): block 2 is referenced
(private 0, global 1)
FATAL 1:  VACUUM (vc_repair_frag): FlushRelationBuffers returned -2