Re: Collations and Replication; Next Steps

On Wed, Sep 17, 2014 at 9:07 AM, Matthew Kelly <mkelly@tripadvisor.com> wrote:
> Here is where I think the timezone and PostGIS cases are fundamentally different:
> I can pretty easily make sure that all my servers run in the same timezone.  That's just good practice.  I'm also going to install the same version of PostGIS everywhere in a cluster.  I'll build PostGIS and its dependencies from the exact same source files, regardless of when I build the machine.
>
> Timezone is a user level setting; PostGIS is a user level library used by a subset.
>
> glibc is a system level library, and text is a core data type, however.  Changing versions to something that doesn't match the kernel can lead to system level instability, broken linkers, etc.  (I know because I tried).  Here are some subtle other problems that fall out:
>
>  * Upgrading glibc, the kernel, and linker through the package manager in order to get security updates can cause the corruption.
>  * A basebackup that is taken in production and placed on a backup server might not be valid on that server, or your desktop machine, or on the spare you keep to do PITR when someone screws up.
>  * Unless you keep _all_ of your clusters on the same OS, machines from your database spare pool probably won't be the right OS when you add them to the cluster because a member failed.
>
> Keep in mind here, by OS I mean CentOS versions.  (we're running a mix of late 5.x and 6.x, because of our numerous issues with the 6.x kernel)
>
> The problem with LC_IDENTIFICATION is that every machine I have seen reports revision "1.0", date "2000-06-24".  It doesn't seem like the versioning is being actively maintained.
>
> I'm with Martjin here, lets go ICU, if only because it moves sorting to a user level library, instead of a system level.  Martjin do you have a link to the out of tree patch?  If not I'll find it.  I'd like to apply it to a branch and start playing with it.

What I find astonishing is that whoever maintains glibc (or the Red
Hat packaging for it) thinks it's OK to change the collation order in
a minor release.  I'd understand changing it between, say, RHEL 6 and
RHEL 7.  But the idea that minor release, supposedly safe updates
think they can whack this around without breaking applications really
kind of blows my mind.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company