Help. The database was created using collation version 2.17, but the operating system provides version 2.34.

Hello,

I am in the process of migrating DB to Alma9 host. The databse
is rather large - few TBs.

I have run pg_basebackup on Alma9 host and established replication from production to it. The idea is to quickly switch from master to this new host during downtime.

Establishing replication went fine. Source postgresql version is 15.6, destination is 15.7

When I psql into replica I get:

WARNING: database "xxx" has a collation version mismatch
DETAIL: The database was created using collation version 2.17, but the operating system provides version 2.34.
HINT: Rebuild all objects in this database that use the default collation and run ALTER DATABASE xxx REFRESH COLLATION VERSION, or build PostgreSQL with the right library version.

Looking up the issue the solution seems to be

REINDEX database xxx
ALTER DATABASE xxx REFRESH COLLATION VERSION

But this defeats the whole idea of having short downtime because REINDEX will take forever.

What is this "or build PostgreSQL with the right library version"?
Is this about 15.7 vs 15.6 or is it about different glibc version between RH7 and Alma9?

Is there a better way to handle it? I cannot afford long downtime.
This came up rather unexpectedly and I am now in a tight situation having to find solution fast. I do not recall having similar issue when going from RH6 to RH7.

Thank you for your help.