Horton

Thread

  1. PiTR and other architectures....

    Philip Warner <pjw@rhyme.com.au> — 2008-12-02T12:02:12Z

    Having just tried to restore a 64 bit BSD database to a 32 bit linux
machine (using PiTR), I have now realized the (with hindsight, obvious)
error in my ways.

Now, I need to plan a way forward. From reading of other peoples similar
problems, I now realize that I need a system with identical on-disk
formats. Question is:

Is there a simple way to determine compatibility? (eg. a small
well-defined list of requirements)

In the specific instance I am working with, I'd like to copy from 64 bit
AMD BSD system to a 64 bit Linux system.

Philip Warner

  2. Re: PiTR and other architectures....

    Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> — 2008-12-02T14:21:09Z

    Philip Warner wrote:
> Having just tried to restore a 64 bit BSD database to a 32 bit linux
> machine (using PiTR), I have now realized the (with hindsight, obvious)
> error in my ways.
> 
> Now, I need to plan a way forward. From reading of other peoples similar
> problems, I now realize that I need a system with identical on-disk
> formats. Question is:
> 
> Is there a simple way to determine compatibility? (eg. a small
> well-defined list of requirements)

initdb on one platform, copy the data directory over to the other 
system, and try to start postmaster. It will complain if the on-disk 
format is not compatible.

You can also run pg_controlinfo on both systems, and compare the 
results. If the "Maximum data alignment", and all the values below it in 
the pg_controlinfo output match, the formats are compatible.

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com

  3. Re: PiTR and other architectures....

    Andrew Dunstan <andrew@dunslane.net> — 2008-12-02T16:12:18Z

    
Heikki Linnakangas wrote:
>
> You can also run pg_controlinfo on both systems, and compare the 
> results. If the "Maximum data alignment", and all the values below it 
> in the pg_controlinfo output match, the formats are compatible.
>

s/pg_controlinfo/pg_controldata/

cheers

andrew

  4. Re: PiTR and other architectures....

    Jeff Davis <pgsql@j-davis.com> — 2008-12-02T18:07:57Z

    On Tue, 2008-12-02 at 16:21 +0200, Heikki Linnakangas wrote:
> initdb on one platform, copy the data directory over to the other 
> system, and try to start postmaster. It will complain if the on-disk 
> format is not compatible.
> 
> You can also run pg_controlinfo on both systems, and compare the 
> results. If the "Maximum data alignment", and all the values below it in 
> the pg_controlinfo output match, the formats are compatible.

I don't think these things will work for all differences that could be
problematic. For instance, a GNU system has a different collation for
the en_US locale than an OS X system. This means that the indexes built
using en_US on one system can't be moved to the other.

How would either of these tests be able to determine that the systems
are incompatible?

I don't think this is a problem between GNU and FreeBSD, however, so
this may work in Philip's case.

Regards,
	Jeff Davis

  5. Re: PiTR and other architectures....

    Simon Riggs <simon@2ndquadrant.com> — 2008-12-02T19:15:19Z

    On Tue, 2008-12-02 at 23:02 +1100, Philip Warner wrote:

> In the specific instance I am working with, I'd like to copy from 64
> bit AMD BSD system to a 64 bit Linux system.

I wouldn't recommend it. Midnight is the wrong time to find out that
there was a difference that mattered after all. Is the risk worth it?

-- 
 Simon Riggs           www.2ndQuadrant.com
 PostgreSQL Training, Services and Support

  6. Re: PiTR and other architectures....

    Philip Warner <pjw@rhyme.com.au> — 2008-12-02T23:15:15Z

    Jeff Davis wrote:
> On Tue, 2008-12-02 at 16:21 +0200, Heikki Linnakangas wrote:
>   
>> initdb on one platform, copy the data directory over to the other 
>> system, and try to start postmaster. It will complain if the on-disk 
>> format is not compatible.
>>
>> You can also run pg_controlinfo on both systems, and compare the 
>> results. If the "Maximum data alignment", and all the values below it in 
>> the pg_controlinfo output match, the formats are compatible.
>>     
>
> I don't think these things will work for all differences that could be
> problematic. For instance, a GNU system has a different collation for
> the en_US locale than an OS X system. This means that the indexes built
> using en_US on one system can't be moved to the other.
>
> How would either of these tests be able to determine that the systems
> are incompatible?
>
>   

wow...that's a little scary. Sounds like there is no trustworthy test I
can run. Other than the case of collation differences, are there any
other kinds of problems that would not be detected by even a postmaster
restart?



                                 |/

  7. Re: PiTR and other architectures....

    Jeff Davis <pgsql@j-davis.com> — 2008-12-02T23:44:28Z

    On Wed, 2008-12-03 at 10:15 +1100, Philip Warner wrote:
> wow...that's a little scary. Sounds like there is no trustworthy test I
> can run. Other than the case of collation differences, are there any
> other kinds of problems that would not be detected by even a postmaster
> restart?
> 

I can't answer that question authoritatively. If the locales obey the
same rules, and pg_controldata has the same output for the relevant
values (as Heikki mentioned), I *think* it will work.

But, as Simon pointed out, is it really worth the risk? PITR is closer
to a physical process, and it's probably wise to just assume it's not
portable.

Regards,
	Jeff Davis

  8. Re: PiTR and other architectures....

    Philip Warner <pjw@rhyme.com.au> — 2008-12-03T00:02:50Z

    >
> But, as Simon pointed out, is it really worth the risk? PITR is closer
> to a physical process, and it's probably wise to just assume it's not
> portable.
>   

Yeah...I am getting that impression ;-). From this I will assume we need:

 - same OS (and OS minor version?)
 - same CPU architecture

I was hoping it was a simple set of requirements, but that's life.


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