Unable to Connect to DB Instance

Good Morning,

Beginning yesterday morning, users have been unable to fully connect to our DB Instance.

1. At the time of the initial report - I was connected to the DB via pgAdmin and could perform queries without problem.

2. Users reported messages similar to "could not open file "global/11801": No such file or directory"

3. At that time, connection logging was turned off and there were no messages in the log files.

4. As this is a development environment, I turned logging on in the config and restarted the DB

5. After restart, neither I, nor the Users could fully reconnect.

6. I have performed a SYS Level backup (tar of the whole postgres directory tree)

7. I cannot perform a DB level Backup (same errors occur)

System Details
Linux Debian 7.11
Postgres 9.1 (9.1.24lts-0+d)

It appears that we can connect to the DB Server itself as I get "connection received" and "connection authorized" - but when trying to access the DB itself, several errors are raised (see below).
I am assuming that some internals are no longer consistent - the file "global/11801" for instance really does not exist on the system.

Questions:

1. Is there any way to recover from this (backup is unfortunately rather old)

2. What are possible causes? I'd like to prevent this from happening on my production servers.

** I am aware that we are on older releases, and yes, we plan to migrate to more current releases "soon" (tm) ...

Thanks in advance.

John Boblitz

Exceprt from Log:
2018-07-04 09:15:13 CEST 192.168.250.50(28559) [unknown]LOG: connection received: host=192.168.250.50 port=28559
2018-07-04 09:15:14 CEST 192.168.250.50(28559) postgresLOG: connection authorized: user=dbadmin database=postgres
2018-07-04 09:15:14 CEST 192.168.250.50(28559) postgresERROR: could not open file "global/11801": No such file or directory
2018-07-04 09:15:14 CEST 192.168.250.50(28559) postgresSTATEMENT: SELECT usecreatedb, usesuper, CASE WHEN usesuper THEN pg_postmaster_start_time() ELSE NULL END as upsince, CASE WHEN usesuper THEN pg_conf_load_time() ELSE NULL END as confloadedsince, CASE WHEN usesuper THEN pg_is_in_recovery() ELSE NULL END as inrecovery, CASE WHEN usesuper THEN pg_last_xlog_receive_location() ELSE NULL END as receiveloc, CASE WHEN usesuper THEN pg_last_xlog_replay_location() ELSE NULL END as replayloc, CASE WHEN usesuper THEN pg_last_xact_replay_timestamp() ELSE NULL END as replay_timestamp, CASE WHEN usesuper AND pg_is_in_recovery() THEN pg_is_xlog_replay_paused() ELSE NULL END as isreplaypaused
FROM pg_user WHERE usename=current_user
2018-07-04 09:15:19 CEST 192.168.250.50(28559) postgresERROR: could not open file "global/11801": No such file or directory
2018-07-04 09:15:19 CEST 192.168.250.50(28559) postgresSTATEMENT: SELECT rolcreaterole, rolcreatedb FROM pg_roles WHERE rolname = current_user;
2018-07-04 09:15:22 CEST 192.168.250.50(28561) [unknown]LOG: connection received: host=192.168.250.50 port=28561
2018-07-04 09:15:22 CEST 192.168.250.50(28561) g11BaseLOG: connection authorized: user=dbadmin database=g11Base
2018-07-04 09:15:23 CEST 192.168.250.50(28561) g11BaseERROR: could not open file "pg_tblspc/24579/PG_9.1_201105231/24580/11866": No such file or directory
2018-07-04 09:15:23 CEST 192.168.250.50(28561) g11BaseSTATEMENT: SELECT CASE WHEN nspname LIKE E'pg\\_temp\\_%' THEN 1
WHEN (nspname LIKE E'pg\\_%') THEN 0
ELSE 3 END AS nsptyp,
nsp.nspname, nsp.oid, pg_get_userbyid(nspowner) AS namespaceowner, nspacl, description, has_schema_privilege(nsp.oid, 'CREATE') as cancreate,
(SELECT array_agg(label) FROM pg_seclabels sl1 WHERE sl1.objoid=nsp.oid) AS labels,
(SELECT array_agg(provider) FROM pg_seclabels sl2 WHERE sl2.objoid=nsp.oid) AS providers
FROM pg_namespace nsp
LEFT OUTER JOIN pg_description des ON (des.objoid=nsp.oid AND des.classoid='pg_namespace'::regclass)
WHERE NOT ((nspname = 'pg_catalog' AND EXISTS (SELECT 1 FROM pg_class WHERE relname = 'pg_class' AND relnamespace = nsp.oid LIMIT 1)) OR
(nspname = 'pgagent' AND EXISTS (SELECT 1 FROM pg_class WHERE relname = 'pga_job' AND relnamespace = nsp.oid LIMIT 1)) OR
(nspname = 'information_schema' AND EXISTS (SELECT 1 FROM pg_class WHERE relname = 'tables' AND relnamespace = nsp.oid LIMIT 1)) OR
(nspname LIKE '_%' AND EXISTS (SELECT 1 FROM pg_proc WHERE proname='slonyversion' AND pronamespace = nsp.oid LIMIT 1))
) AND nspname NOT LIKE E'pg\\_temp\\_%'AND nspname NOT LIKE E'pg\\_toast_temp\\_%' ORDER BY 1, nspname