hidden junk files in ...data/base/oid/

Hello,

I ran upgrade from 9.1 to 9.3 on CentOS using pg_upgrade and database
cluster size dropped from 77GB to 4.3GB. I wonder how this could happen. No
data lost. This means I had about 70GB junk files in my database...

I checked top 10 biggest database tables: nearly same size on old/new
cluster, the biggest table about 2GB, next 1GB, all other tables smaller
and smaller..
I checked files of biggest database (/var/lib/pgsql/9.1/data/base/27610):

# du -sm * |awk '{s+=$1} END {print s}'
7107
# du -sm . |sort -n
75264 .

So size of non-hidden database files is 1/10th of the whole database size.

Question: Where does the 70GB hidden files in ...data/base/oid/ come
from? Which postgres process could generate them? Some missed
maintenance from my side? A bug? Anybody else experienced such issue?

Thanks, Andrej

---------details: ...data/base/oid file listing shortened:

# ls -la
total 77069960
drwx------. 2 postgres postgres 32768 May 12 18:50 .
drwxr-xr-x. 5 postgres postgres 4096 May 12 11:47 ..
-rw-------. 1 postgres postgres 354156544 Feb 25 12:06 .27623.17rLmT
-rw-------. 1 postgres postgres 338952192 Feb 25 14:21 .27623.6dH1b6
-rw-------. 1 postgres postgres 5767168 Mar 7 16:00 ..27623.6dH1b6.6PrU4B
-rw-------. 1 postgres postgres 411041792 Feb 25 15:07 .27623.aN42DG
-rw-------. 1 postgres postgres 342884352 Mar 8 15:16 ..27623.aN42DG.0U5xfj
-rw-------. 1 postgres postgres 343146496 Mar 8 13:13 ..27623.aN42DG.2WFmNo
-rw-------. 1 postgres postgres 343408640 Mar 8 10:43 ..27623.aN42DG.384SXU
-rw-------. 1 postgres postgres 357302272 Mar 8 05:26 ..27623.aN42DG.3hHjZ8
-rw-------. 1 postgres postgres 360185856 Mar 7 18:19 ..27623.aN42DG.5lWta4
-rw-------. 1 postgres postgres 343146496 Mar 8 10:12 ..27623.aN42DG.64lNVQ

...shortened...

-rw-------. 1 postgres postgres 1005322240 Feb 25 15:38 .27731.2.JKYXGW
-rw-------. 1 postgres postgres 359661568 Mar 9 14:52 ..27731.2.JKYXGW.3h8RuF
-rw-------. 1 postgres postgres 331087872 Mar 9 07:37 ..27731.2.JKYXGW.3hK5aF
-rw-------. 1 postgres postgres 359923712 Mar 9 09:29 ..27731.2.JKYXGW.3KA5Cq
-rw-------. 1 postgres postgres 359923712 Mar 9 16:55 ..27731.2.JKYXGW.45nQei
-rw-------. 1 postgres postgres 137363456 Mar 9 04:47 ..27731.2.JKYXGW.4zya2Z

...shortened...

-rw-------. 1 postgres postgres 769916928 Feb 25 15:53 .27902.YboxvS
-rw-------. 1 postgres postgres 671612928 Feb 20 10:01 .27902.YMEtoS
-rw-------. 1 postgres postgres 159645696 Feb 25 16:24 .59866.Lkyxgs
-rw-------. 1 postgres postgres 272629760 Feb 20 18:37 .59866.RTcUkC
-rw-------. 1 postgres postgres 505151488 Feb 25 16:40 .59961.5BcZpK
-rw-------. 1 postgres postgres 91750400 Feb 25 16:55 .60194.gUqSdJ
-rw-------. 1 postgres postgres 8192 Apr 7 05:20 60592
-rw-------. 1 postgres postgres 8192 Jan 31 13:03 60594
-rw-------. 1 postgres postgres 8192 Apr 7 02:01 60596
-rw-------. 1 postgres postgres 8192 Feb 28 14:44 60598
-rw-------. 1 postgres postgres 8192 Apr 7 11:55 60600

...shortened...

-rw-------. 1 postgres postgres 139264 May 12 12:08 702364
-rw-------. 1 postgres postgres 24576 May 9 12:42 702364_fsm
-rw-------. 1 postgres postgres 8192 May 9 12:40 702364_vm
-rw-------. 1 postgres postgres 0 May 9 10:10 702369
-rw-------. 1 postgres postgres 860160 May 12 12:08 702372
-rw-------. 1 postgres postgres 24576 May 9 12:37 702372_fsm
-rw-------. 1 postgres postgres 8192 May 9 12:42 702372_vm
-rw-------. 1 postgres postgres 8192 May 9 10:10 702377
-rw-------. 1 postgres postgres 499712 May 12 12:08 702381

...shortened...

-rw-------. 1 postgres postgres 16384 May 9 14:34 704207
-rw-------. 1 postgres postgres 16384 May 9 14:34 704208
-rw-------. 1 postgres postgres 8192 May 9 14:34 704209
-rw-------. 1 postgres postgres 16384 May 9 14:34 704210
-rw-------. 1 postgres postgres 16384 May 9 14:34 704211
-rw-------. 1 postgres postgres 512 May 9 14:34 pg_filenode.map
-rw-------. 1 postgres postgres 106804 May 12 18:50 pg_internal.init
-rw-------. 1 postgres postgres 4 Jan 28 13:52 PG_VERSION