Re: Collations and Replication; Next Steps

From: Matthew Kelly <mkelly(at)tripadvisor(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Martijn van Oosterhout <kleptog(at)svana(dot)org>, Peter Geoghegan <pg(at)heroku(dot)com>, Peter Eisentraut <peter_e(at)gmx(dot)net>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, "Matthew Spilich" <mspilich(at)tripadvisor(dot)com>
Subject: Re: Collations and Replication; Next Steps
Date: 2014-09-17 14:06:53
Message-ID: 6824A5EF-4D25-47F6-8AB5-6C450B554587@tripadvisor.com
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-hackers

Let me double check that assertion before we go too far with it.

Most of the problems I've seen are across 5 and 6 boundaries. I thought I had case where it was within a minor release but I can't find it right now. I'm going to dig.

That being said the sort order changes whether you statically or dynamically link (demonstrated on 4+ machines running different linux flavors), so at the point I have no reason to trust the stability of the sort across any build. I legitimately question whether strcoll is buggy. Ex. I have cases where for three strings a, b and c: a > b, but (a || c) < (b || c). That's right postfixing doesn't hold. It actually calls into question the index scan optimization that occurs when you do LIKE 'test%' even on a single machine, but I don't want to bite that off at the moment.

My mentality has switched to 'don't trust any change until shown otherwise', so that may have bled into my last email.

- Matt K.

On Sep 17, 2014, at 8:17 AM, Robert Haas <robertmhaas(at)gmail(dot)com>
wrote:

> On Wed, Sep 17, 2014 at 9:07 AM, Matthew Kelly <mkelly(at)tripadvisor(dot)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

In response to

Responses

Browse pgsql-hackers by date

  From Date Subject
Next Message Greg Stark 2014-09-17 14:46:42 Re: Collations and Replication; Next Steps
Previous Message Dev Kumkar 2014-09-17 13:51:43 Re: pg_multixact issues