Regarding query on the postgresql upgrade

Dear All,

We have a database server which is installed postgresql 9.2.13 version
which is connected to our Atlassian applications.We have connected single
database server to all the Atlassian applications
(Jira,Confluence,BitBucket,Eazybi,Fisheye/Crucible).

We are planning to upgrade the postgres version from 9.2.13 to 9.4.25 by
keeping the support version of Atlassian in mind.

We are able to perform the upgrade on our test database environment which
is connected to (Jira,Confluence,BitBucket,Fisheye/Crucible) applications
and connected to all the applications without any issues.

But to proceed the same in production, we have tried to run the pgdump
command to take the backup of all the databases and getting the below error
when we tried to take the dump of Eazybi database which is not present on
our stage environment.

pg_dump: Dumping the contents of table "source_cubes" failed: PQgetResult()
failed.

pg_dump: Error message from server: ERROR: missing chunk number 0 for
toast value 11934509 in pg_toast_1179885

Upon investigation we have found that the issue is because of the
corruption in the public schema of the eazybi database and to resolve the
issue we have found the steps in the link
https://gist.github.com/supix/80f9a6111dc954cf38ee99b9dedf187a.

But we are not sure if the reindexing will cause any harm to the databases
to the other application databases which are present in the same server.

Could you please help us to understand the below queries.

1. If we do an upgrade, keeping the corrupted database will there be
any issues ?

2. During upgrade does postgres have any changes to the schema's of the
existing databases?

3. Is there any recommended cleanup procedure to clean the postgres
database to give good performance?

4. How can we resolve the connection pool spikes on the database?

5. Any other tip/suggestions which we need to keep in mind while performing
a postgres upgrade.

Thanks and Regards,

Ramesh Penuballi