Index corruption & broken clog

Hi,

One of my PostgreSQL server crashed badly yesterday. A process was killed
(see dmesg below) and postgres was stuck with theses process:

postgres 2083 1 0 Oct08 ? 00:19:02
/usr/lib/postgresql/9.5/bin/postgres -D /home/postgres/data/issss090/systeme
postgres 2221 2083 0 Oct08 ? 00:02:03 postgres: issss090: logger
process
postgres 14068 2083 8 Oct09 ? 02:50:22 [postgres]
postgres 19668 19665 0 09:40 pts/0 00:00:00 -su

I couldn't stop it with "pg_ctl stop immediate". We had to kill them and
release the shared memory block.

dmesg showed this.

[Tue Oct 10 07:45:29 2017] postgres[25506]: segfault at 7f2253ecb000 ip
00007f225aead994 sp 00007ffc2a9c0c28 error 4 in libc-2.23.so
[7f225ae0e000+1c0000]
[Tue Oct 10 07:45:30 2017] BUG: Bad rss-counter state mm:ffff8800516a7c00
idx:0 val:178
[Tue Oct 10 07:45:31 2017] BUG: Bad page map in process postgres
pte:4800000090248c8d pmd:2c3de067

When I checked the postgresql log I found lots of these :

could not read block 76638 in file
"pg_tblspc/16395/PG_9.5_201510051/16396/20082": read only 0 of 8192 bytes
could not read block 76669 in file
"pg_tblspc/16395/PG_9.5_201510051/16396/19993": read only 0 of 8192 bytes
index "degrade_pkey" contains corrupted page at block 60392
index "degrade_pkey" contains unexpected zero page at block 60392
index "idx_coor_brute_geometrie" contains corrupted page at block 53061
index "idx_coor_brute_geometrie" contains corrupted page at block 56109
index "idx_coor_brute_geometrie" contains corrupted page at block 58867
index "idx_coor_brute_geometrie" contains corrupted page at block 59003
index "idx_coor_brute_geometrie" contains corrupted page at block 60138
index "idx_coor_brute_geometrie" contains corrupted page at block 71974
index "idx_coor_brute_geometrie" contains corrupted page at block 80968
index "idx_coor_brute_geometrie" contains corrupted page at block 86777
index "idx_coor_brute_geometrie" contains unexpected zero page at block
78586
index "idx_coor_proj_ligne_geometrie" contains corrupted page at block
64349
index "idx_numero_course" contains corrupted page at block 3435
index "idx_numero_course" contains corrupted page at block 7176
index "idx_numero_engin" contains corrupted page at block 30996
index "idx_utc_envoi_composant_amont" contains corrupted page at block
76497
index "idx_utc_envoi_reseau" contains corrupted page at block 76524
right sibling's left-link doesn't match: block 102923 links to 49947
instead of expected 1 in index "idx_utc_reception_fournisseur"
right sibling's left-link doesn't match: block 103014 links to 51087
instead of expected 1 in index "idx_utc_reception_composant_amont"
right sibling's left-link doesn't match: block 76978 links to 59148
instead of expected 1 in index "idx_utc_envoi_reseau"
right sibling's left-link doesn't match: block 77073 links to 82204
instead of expected 1 in index "idx_utc_envoi_composant_amont"

The errors started to show up on inserts 8 hours before the crash.
I dont understand because when I look into theses pages with pageinspect
they are not empty / dont look bad.
For exemple, this "SELECT * FROM bt_page_items('degrade_pkey',60392);"
showed a normal page but the error messages claims its zeroed.

I checked the tables for duplicates on the primary key. Checksum are
enabled and I didn't get any error message when I scanned the tables.
I found 77 duplicates on one table and this:

ERROR: could not access status of transaction 3443523584
DETAIL: Could not open file "pg_clog/0CD4": No such file or directory.

I dont think this transaction ever existed given the files I found in the
clog directory.

postgres(at)ulbdgomp01:~/data/igomp090/systeme/pg_clog$ ls -al
total 30292
drwx------ 2 postgres postgres 4096 Oct 9 22:50 .
drwx------ 18 postgres postgres 4096 Oct 12 02:32 ..
-rw------- 1 postgres postgres 262144 Aug 16 22:50 0000
-rw------- 1 postgres postgres 262144 Aug 17 16:20 0001
-rw------- 1 postgres postgres 262144 Aug 17 22:25 0002
...
-rw------- 1 postgres postgres 262144 Oct 7 19:31 0072
-rw------- 1 postgres postgres 262144 Oct 9 22:50 0073
-rw------- 1 postgres postgres 122880 Oct 12 11:56 0074

In your opinion :
* am I missing a (lots of) clog file(s) or is it a error in the heap page
giving an erroneous txid ?
* Is there a way to find which row has the transaction number 3443523584
(in t_xmin t_xmax I suppose)?
* Why am I not seeing any obiously broken page when I check with
pageinspect ?

We are using:
* Ubuntu 16.04 LTS
* PotgreSQL 9.5.8 on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu
5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609, 64-bit

Thx a lot.

Benoit.