Cluster on NAS and data center.

On 4 July 2016 at 17:33, Krzysztof Kaczkowski <grafvader@gmail.com> wrote:

Hello everyone,

Right now we have PostgreSQL on Windows Server (main data center) and
cluster is placed on NAS. We have emergency data center on UNIX
architecture. We want that emergency data center could continue work on
PostgreSQL cluster that has been used by Windows PostgreSQL.

We know that standard PostgreSQL is not able to use cluster created on
different OS. We think that recompilation PostgreSQL with some specific
flags. This should give us compatibility of cluster on different Systems.
We see a small differences in cluster files on binary level. Can You help
us pick proper compilation flags?

I wouldn't recommend that, and it might be pretty tricky.

Windows is an LLP64 architecture, and *nix is usually LP64. Because
PostgreSQL's data directory format is directly tied to the size of data
types in the host operating system this might cause you problems. See
http://stackoverflow.com/a/384672/398670 . sizeof(long) will differ.

I'd love to break that particular assumption if/when an on-disk format
break is done, since it's very unfortunate that PostgreSQL on one
architecture/OS won't read data directories from another architecture/OS.
But for now we're fairly stuck with it AFAIK.

Why can'y you just deploy a Windows backup cluster?

--
Craig Ringer http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services

Hello,

About Your question, please do not ask. This infrastructure is an outcome
of a very long talk with supervisors.

Back to the topic. I like the tricky part. Do You think there is some way
to achieve this on compilation level or shall we search somewhere else? For
example UNIX libraries or even change and recompile kernel?

Craig Ringer <craig@2ndquadrant.com> writes:

On 4 July 2016 at 17:33, Krzysztof Kaczkowski <grafvader@gmail.com> wrote:

We know that standard PostgreSQL is not able to use cluster created on
different OS. We think that recompilation PostgreSQL with some specific
flags. This should give us compatibility of cluster on different Systems.
We see a small differences in cluster files on binary level. Can You help
us pick proper compilation flags?

I wouldn't recommend that, and it might be pretty tricky.

Indeed. Aside from architectural differences, I'd be very afraid of
differences in collation order (resulting in incompatible indexes on
textual columns). You might be able to make it work if you only ever
use "C" locale. But really, this is not and will never be considered
supported usage, and if it fails, no one is going to say anything
except "we warned you not to do that".

regards, tom lane

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As someone who has bitten by index corruption due to collation changes
between glibc versions that shipped CentOS 6 and CentOS 7, don't even try
to do this with anything other than C collation. The default collation
_will_ deterministically leave you with a silently corrupt database if you
store anything other than ASCII text. Windows and Linux are going to
implement en_US.utf-8 slightly differently and Postgres is currently
relying on the OS to provide collation implementations. Go search for my
mailing list post about the dangers of running across versions of glibc for
more info.

I'm going to echo everyone else's sentiment though, and assert that what
you are trying to do is really an insane idea. You might be able to make it
appear like its working but as a DBA, I would have absolutely no confidence
in using that server for disaster recovery.

If your company is saving money by not getting Windows licenses for your DR
environment, you are far better off just saving one more license and making
both your production and DR server be Linux builds.

- Matt K.

Hello,

Thanks to emails, we have achieved what we wanted. This is what we’ve done:

Compilation (for 32 bit version, initdb with locale=C):

CFLAGS="-mx32 -fexcess-precision=standard -O2"
CXXFLAGS="-mx32"

configure --without-zlib --disable-float8-byval --without-readline
--host=x86_64-linux-gnux32

We also have installed libx32.

Right now we received cluster that is fully manageable from both systems.
Anyone see something dangerous with this compilation?

On Tue, Jul 5, 2016 at 7:46 AM, Krzysztof Kaczkowski
<grafvader@gmail.com> wrote:

Thanks to emails, we have achieved what we wanted. This is what we’ve done:

Compilation (for 32 bit version, initdb with locale=C):

CFLAGS="-mx32 -fexcess-precision=standard -O2"
CXXFLAGS="-mx32"

configure --without-zlib --disable-float8-byval --without-readline
--host=x86_64-linux-gnux32

We also have installed libx32.

Right now we received cluster that is fully manageable from both systems.
Anyone see something dangerous with this compilation?

That seems to cover a fair amount of territory, but it might be unwise
to assume that there are no other issues.

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

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