Hello,

We have a bunch of existing Postgres 10 clusters running on CentOS 7, which have been initialized (initdb) with these collation options;

-E 'UTF-8'
--lc-collate=sv_SE.UTF-8
--lc-ctype=sv_SE.UTF-8
--lc_monetary=sv_SE.UTF-8
--lc-numeric=sv_SE.UTF-8
--lc-time=sv_SE.UTF-8
--lc-messages=en_US.UTF-8

And createdb were provided with these locale options when setting up databases:
--lc-collate=sv_SE.UTF-8
--lc-ctype=sv_SE.UTF-8

\l in psql gives:

         Name         |          Owner           | Encoding | Collate   |    Ctype    |
----------------------+--------------------------+----------+-------------+-------------+
 test-db              | test-user                | UTF8     | sv_SE.UTF-8 | sv_SE.UTF-8 |


We're upgrading the servers using logical replication, and would like to take the opportunity to switch to ICU rather than relying on glibc, to avoid future problems with index corruption if using physical replication between servers with different versions of glibc.

We're trying to figure out the most correct way to configure postgres to achieve this. Currently we have:

-E 'UTF-8'
--locale-provider=icu
--icu-locale=sv-SE-x-icu

And createdb are provided with locale options:
--lc-collate=C
--lc-ctype=C

\l in psql now gives:

        Name         |        Owner        | Encoding | Collate   |    Ctype    | ICU Locale  | Locale Provider |
---------------------+---------------------+----------+-------------+-------------+-------------+-----------------+
 test-db             | test-user           | UTF8     | C           | C           | sv-SE-x-icu | icu             |

Is this a safe configuration to avoid index corruption, and other problems, while still being compatible with the previous locale settings? We have done some testing and it appears ORDER BY does sort rows according to Swedish localization in the ICU configured test-db.

We're uncertain since this blogpost -> https://peter.eisentraut.org/blog/2022/09/26/icu-features-in-postgresql-15 mentions that there are still some postgres code relying on libc locale facilities. Should we set lc-collate and lc-ctype to sv_SE.UTF-8 when creating databases in addition to the ICU options provided to initdb due to this? Will we still be safe from glibc related corruption as long as --locale-provider=icu --icu-locale=sv-SE-x-icu is set?

Best Regards,

Oscar


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