Re: Uber migrated from Postgres to MySQL

On Thu, Jul 28, 2016 at 6:32 PM, Alex Ignatov <a(dot)ignatov(at)postgrespro(dot)ru>
wrote:

>
> On 28.07.2016 18:41, Igor Neyman wrote:
>
>> -----Original Message-----
>> From: Alex Ignatov [mailto:a(dot)ignatov(at)postgrespro(dot)ru]
>> Sent: Thursday, July 28, 2016 11:26 AM
>> To: Igor Neyman <ineyman(at)perceptron(dot)com>; Rakesh Kumar <
>> rakeshkumar464a3(at)gmail(dot)com>
>> Cc: PostgreSQL General <pgsql-general(at)postgresql(dot)org>
>> Subject: Re: [GENERAL] Uber migrated from Postgres to MySQL
>>
>>
>> On 28.07.2016 18:09, Igor Neyman wrote:
>>
>>> -----Original Message-----
>>> From: pgsql-general-owner(at)postgresql(dot)org
>>> [mailto:pgsql-general-owner(at)postgresql(dot)org] On Behalf Of Alex Ignatov
>>> Sent: Thursday, July 28, 2016 10:59 AM
>>> To: Rakesh Kumar <rakeshkumar464a3(at)gmail(dot)com>
>>> Cc: PostgreSQL General <pgsql-general(at)postgresql(dot)org>
>>> Subject: Re: [GENERAL] Uber migrated from Postgres to MySQL
>>>
>>>
>>> On 28.07.2016 17:50, Rakesh Kumar wrote:
>>>
>>>> On Thu, Jul 28, 2016 at 10:38 AM, Alex Ignatov <
>>>> a(dot)ignatov(at)postgrespro(dot)ru> wrote:
>>>>
>>>> Sorry, what? You can rollback to previous version of software what you
>>>>> had.
>>>>>
>>>>> https://docs.oracle.com/cd/E11882_01/server.112/e23633/downgrade.htm
>>>>> #
>>>>> UPGRD007
>>>>>
>>>> Not so fast. This requires the db to be set in compatibility mode of
>>>> the lower version. Once that is removed, no downgrade is possible.
>>>>
>>>> Also starting from Oracle 12 this downgrade option has been removed.
>>>> That is, you can't upgrade in-place from Or 11 to 12 and then
>>>> downgrade back. The only supported way is the restore from an old
>>>> backup (which is true for all products). I don't work in Oracle, but
>>>> got this clarified by someone who is an Oracle dba.
>>>>
>>>>
>>>> Not true -
>>>
>>> https://docs.oracle.com/database/121/UPGRD/downgrade.htm#UPGRD007
>>>
>>> About compatible params you are right but downgrade is possible from 12c.
>>>
>>> Alex Ignatov
>>> Postgres Professional: http://www.postgrespro.com The Russian Postgres
>>> Company
>>>
>>> ______________________________________________________________________
>>> _______
>>>
>>> Alex, documentation you point to just proves what Rakesh said:
>>>
>>> "For supported releases of Oracle Database, you can downgrade a database
>>> to the release from which you last upgraded. For example, if you recently
>>> upgraded from release 11.2.0.4 to Oracle Database 12c, and you did not
>>> change the compatible initialization parameter to 12.1 or higher, then you
>>> can downgrade to release 11.2.0.4."
>>>
>>> So, you can downgrade only if you didn't "activate" newer feature
>>> (didn't compatibility to higher version).
>>> But then, what's the point in upgrading (I know, there are some like bug
>>> fixes, etc...), if you aren't going to use newer features.
>>>
>>> Regards,
>>> Igor
>>>
>> Not true again.
>>
>> From Oracle docs
>> https://docs.oracle.com/database/121/UPGRD/intro.htm#UPGRD001 Section
>> "How the COMPATIBLE Initialization Parameter Operates in Oracle Database"
>> -
>> If you run an Oracle Database 12c database with the COMPATIBLE
>> initialization parameter set to 11.0.0, then it generates database
>> structures on disk that are compatible with Oracle Database 11g.
>> Therefore, the COMPATIBLE initialization parameter enables or disables
>> the use of features. If you try to use any new features that make the
>> database incompatible with the COMPATIBLE initialization parameter, then an
>> error occurs. However, any new features that do not make incompatible
>> changes on disk are enabled.
>>
>> So if feature do not change disk in incompatible way this features is
>> enable.
>>
>> Also from this
>>
>> https://docs.oracle.com/database/121/REFRN/GUID-6C57EE11-BD06-4BB8-A0F7-D6CDDD086FA9.htm#REFRN10019
>> :
>>
>> "This parameter specifies the release with which Oracle must maintain
>> compatibility. It enables you to take advantage of the maintenance
>> improvements of a new release immediately in your production systems
>> without testing the new functionality in your environment. Some features of
>> the release may be restricted."
>>
>> So this parameter is made with rollback in mind and you have some new
>> feature from newer software release.
>>
>> Alex Ignatov
>> Postgres Professional:http://www.postgrespro.com
>> The Russian Postgres Company
>>
>>
>> ____________________________________________________________________________________________________________________
>>
>> B.t.w., In Postgres release which doesn't change "database structures"
>> is called "minor" (just replacing binaries), and allows downgrade.
>>
>> "Compactable" or not, in "Oracle world" no DBA in their right mind will
>> attempt major upgrade without having complete (and tested) backup that
>> could be used in case of upgrade going wrong.
>>
>> Regards,
>> Igor
>>
>> Oh, so in contrast to "Oracle world" "Postgres world" DBA in their
> right to do major upgrade without complete and tested backup?
> Ok, I understand you. In Postgres world there always sky is blue and sun
> is shining.

And see, I am just wondering, what DBA in their right mind would allow a db
to run without a complete and tested backup. I mean when you upgrade the
last thing you do is take another backup and the first thing you do after
upgrading is take another backup, right? Or am I just being dense?