Subject: Re: pg_upgrade 9.0 -> 9.3 general questions : things to watch out for
To: pgsql-admin@postgresql.org, bruce@momjian.us
References: <567A510A.1070903@matrix.gatewaynet.com>
 <20151224165540.GA17669@momjian.us>
From: Achilleas Mantzios <achill@matrix.gatewaynet.com>
Message-ID: <568A1F0C.8090907@matrix.gatewaynet.com>
Date: Mon, 4 Jan 2016 09:28:12 +0200
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Thanx Bruce, and a happy new 2016!

On 24/12/2015 18:55, Bruce Momjian wrote:
> On Wed, Dec 23, 2015 at 09:45:14AM +0200, Achilleas Mantzios wrote:
>> Hello List,
>>
>> We just finished a test upgrade using pg_upgrade from 9.0 to 9.3,
>> and the experience has been unexpectedly good! The database is just
> Great.
>
>> a tad smaller than 1TB, and the upgrade last only seconds, using the
>> --link option.
> Yep, the speed is quite unexpected.
>
>> I noticed that :
>> - Database specific options were correctly retained (e.g. bytea_output)
> Yes, that is part of pg_dump.
>
>> - Next XID was correctly transferred to the new cluster
> Yes, that is always done by pg_upgrade.
>
>> I'd like to ask, if we can rely on the above assumptions during the actual migration on the production system.
> Yes.
>
>> Another consideration is --check. I didn't run it on the test
>> system. Is it a requirement? A plus? The doc says about using it in
> --check is only a way to get early warnings about possible failures.
> The checks are also run during an upgrade.
>
>> conjunction with --link to do enable link-mode-specific checks. What
>> does this do? From what I understand, running --check against the
> It makes sure the old and new cluster are on the same file system, which
> is a requirement for hard links.
>
>> existing running older system enables doing some checks and allowing
>> us to perform some preparation work in parallel before the actual
>> final pg_upgrade invocation. Is this true? Can anyone shed some
>> light on this?
> Well, --check really just reports causes of failure before the actual
> upgrade.
>
>> Another question is about --retain (I didn't use it either in our
>> test). I understand that it might transfer or make the links to the
>> old pg_log directory. The doc says "retain SQL and *log* files
>> *even* after a successful completion". What's the logic behind it?
> Uh, it is really just for debugging in case there is a suspicion that
> pg_upgrade is not working properly.
>
>> Why a special note on successful completion? If SQL logs are the
>> regular pg_log files, then which are the other *log* files the doc
>> mentions? Apparently it cannot be WAL (pg_xlog), since this is a
> It is the SQL pg_dump files that were used by pg_upgrade, and the
> postmaster server output log files generated during the upgrade.  Again,
> only useful for debugging of pg_upgrade.
>
>> different format than the old version, and would be of no use in the
>> new data cluster, just like the older PITR archived WALs. So, what's
>> the best practice regarding regular postgresql log file and
>> pg_uprage? How about pg_xlog? Should we just scrap the old ones,
>> move the new ones to the correct locations and re regenerate the
>> symlinks ? Sounds fair, I think.
> pg_xlog files are not portable between major versions of Postgres and
> should never be transfered.  You just delete the old cluster when you
> are done and the old pg_xlog files are removed as part of it.
>


-- 
Achilleas Mantzios
IT DEV Lead
IT DEPT
Dynacom Tankers Mgmt


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