Problem with Upgrading Gitlab

I want to upgrade Gitlab from 10.8.7 to 11.3.4. Still, I found error messages as follows. Can anyone give me solution?

root@ip-10-230-41-219:~# gitlab-rake gitlab:env:info

System information
System: Ubuntu 16.04
Current User: git
Using RVM: no
Ruby Version: 2.3.7p456
Gem Version: 2.6.14
Bundler Version:1.13.7
Rake Version: 12.3.1
Redis Version: 3.2.11
Git Version: 2.16.4
Sidekiq Version:5.0.5
Go Version: unknown

GitLab information
Version: 10.8.7
Revision: eb600b0
Directory: /opt/gitlab/embedded/service/gitlab-rails
DB Adapter: postgresql
SSH Clone URL:
Using LDAP: no
Using Omniauth: no

GitLab Shell
Version: 7.1.2
Repository storage paths:

  • default: /var/opt/gitlab/git-data/repositories
    Hooks: /opt/gitlab/embedded/service/gitlab-shell/hooks
    Git: /opt/gitlab/embedded/bin/git

root@ip-10-230-41-219:~# apt-get install gitlab-ce=11.3.4-ce.0
Reading package lists… Done
Building dependency tree
Reading state information… Done
The following packages will be upgraded:
1 upgraded, 0 newly installed, 0 to remove and 120 not upgraded.
Need to get 0 B/439 MB of archives.
After this operation, 732 kB disk space will be freed.
(Reading database … 205032 files and directories currently installed.)
Preparing to unpack …/gitlab-ce_11.3.4-ce.0_amd64.deb …
gitlab preinstall: Automatically backing up only the GitLab SQL database (excluding everything else!)
Dumping database …
Dumping PostgreSQL database gitlabhq_production … pg_dump: Dumping the contents of table “merge_request_diff_files” failed: PQgetResult() failed.
pg_dump: Error message from server: ERROR: missing chunk number 0 for toast value 86119 in pg_toast_69013
pg_dump: The command was: COPY public.merge_request_diff_files (merge_request_diff_id, relative_order, new_file, renamed_file, deleted_file, too_large, a_mode, b_mode, new_path, old_path, diff, “binary”) TO stdout;
Backup failed
gitlab preinstall:
gitlab preinstall: Backup failed! If you want to skip this backup, run the following command and
gitlab preinstall: try again:
gitlab preinstall:
gitlab preinstall: sudo touch /etc/gitlab/skip-auto-migrations
gitlab preinstall:
dpkg: error processing archive /var/cache/apt/archives/gitlab-ce_11.3.4-ce.0_amd64.deb (–unpack):
subprocess new pre-installation script returned error exit status 1
Errors were encountered while processing:
E: Sub-process /usr/bin/dpkg returned an error code (1)

Looks like your database is corrupted. Googling the error shows Postgres error: Missing chunk 0 for toast value in pg_toast · GitHub and Upgrade Preinstall Unexpected Chunk Size when backing up the Database where I would strongly suggest to take a manual backup and snapshot before proceeding with db fixes.