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ICU Collations and Collation Updates 3+ messages / 3 participants [nested] [flat]
* ICU Collations and Collation Updates @ 2025-04-14 08:28 Thomas Michael Engelke <[email protected]> 0 siblings, 1 reply; 3+ messages in thread From: Thomas Michael Engelke @ 2025-04-14 08:28 UTC (permalink / raw) To: [email protected] Good morning, long time reader, first time writer. Where I currently work my colleagues used libc collations before I arrived. While using libc collations, they stumbled upon the collation update problem after SLES updates (15.4 to 15.5) (collation version difference for database and operating system) (paraphrased, don't have the english message at the hand). For an easy solution I suggested to switch to ICU collations. While documenting the problem for older systems I realized that I did not know enough about the problem to document why ICU collations would solve this problem. After reading https://www.postgresql.org/docs/17/collation.html this is how I understand it: When initdb creates a cluster the OS available collations are copied to the database as database objects, listable using select * from pg_collation; Now, an OS collation update as part of the OS update will change the collations available on the OS level, but not the collations that the database uses. Is my understanding correct then in that this way the database collations never change, unless a manual intervention reinitialises the collations and reindexes the database (or appropriate indexes)? How does that process compare to other RDBMS? Are regular collation updates deemed unnecessary for long running database installations? Or do you people have maintenance workflows that incorporate regular collation updates to the databases? Thanks, Thomas ^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: ICU Collations and Collation Updates @ 2025-04-14 11:05 Laurenz Albe <[email protected]> parent: Thomas Michael Engelke <[email protected]> 0 siblings, 1 reply; 3+ messages in thread From: Laurenz Albe @ 2025-04-14 11:05 UTC (permalink / raw) To: Thomas Michael Engelke <[email protected]>; [email protected] On Mon, 2025-04-14 at 08:28 +0000, Thomas Michael Engelke wrote: > Where I currently work my colleagues used libc collations before I > arrived. While using libc collations, they stumbled upon the collation > update problem after SLES updates (15.4 to 15.5) (collation version > difference for database and operating system) (paraphrased, don't have > the english message at the hand). > > For an easy solution I suggested to switch to ICU collations. While > documenting the problem for older systems I realized that I did not > know enough about the problem to document why ICU collations would > solve this problem. > > After reading https://www.postgresql.org/docs/17/collation.html this is > how I understand it: > > When initdb creates a cluster the OS available collations are copied to > the database as database objects, listable using > > select * from pg_collation; > > Now, an OS collation update as part of the OS update will change the > collations available on the OS level, but not the collations that the > database uses. > > Is my understanding correct then in that this way the database > collations never change, unless a manual intervention reinitialises the > collations and reindexes the database (or appropriate indexes)? How > does that process compare to other RDBMS? > > Are regular collation updates deemed unnecessary for long running > database installations? Or do you people have maintenance workflows > that incorporate regular collation updates to the databases? PostgreSQL just copies the names and versions of the collations to the catalog. The actual collating is done by the C or ICU library. When you update the C library or ICU library and the version changes, you get warned by PostgreSQL and have to rebuild indexes. So the collations can change whenever you update the respective libraries. You would have to build PostgreSQL yourself with a fixed version of ICU that you never upgrade if you want to avoid the problem. Or you start using the POSIX collation. Yours, Laurenz Albe ^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: ICU Collations and Collation Updates @ 2025-04-14 14:36 Tom Lane <[email protected]> parent: Laurenz Albe <[email protected]> 0 siblings, 0 replies; 3+ messages in thread From: Tom Lane @ 2025-04-14 14:36 UTC (permalink / raw) To: Laurenz Albe <[email protected]>; +Cc: Thomas Michael Engelke <[email protected]>; [email protected] Laurenz Albe <[email protected]> writes: > On Mon, 2025-04-14 at 08:28 +0000, Thomas Michael Engelke wrote: >> Is my understanding correct then in that this way the database >> collations never change, unless a manual intervention reinitialises the >> collations and reindexes the database (or appropriate indexes)? How >> does that process compare to other RDBMS? > When you update the C library or ICU library and the version changes, > you get warned by PostgreSQL and have to rebuild indexes. > So the collations can change whenever you update the respective libraries. > You would have to build PostgreSQL yourself with a fixed version of ICU > that you never upgrade if you want to avoid the problem. Yeah. AIUI there are two things that ICU does better than libc here: 1. ICU has a fairly well-defined scheme for identifying collation versions, glibc not so much. So the collation-changed warnings that Laurenz mentions are a lot more trustworthy for ICU collations. 2. It's at least *possible* to use your own fixed-version ICU library if you're desperate enough. I don't think that would work too well for libc; you're stuck with what the platform provides. regards, tom lane ^ permalink raw reply [nested|flat] 3+ messages in thread
end of thread, other threads:[~2025-04-14 14:36 UTC | newest] Thread overview: 3+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2025-04-14 08:28 ICU Collations and Collation Updates Thomas Michael Engelke <[email protected]> 2025-04-14 11:05 ` Laurenz Albe <[email protected]> 2025-04-14 14:36 ` Tom Lane <[email protected]>
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