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Hi all,

So yeah, we could restore the option and put creation of a slave
engine instance to EngineFacade class, but I don't think we want this.

The only reason why slave connections aren't implemented e.g. in
SQLAlchemy is that, SQLAlchemy, as a library can't decide  for you how
those engines should be used: do you have an ACTIVE-ACTIVE setup or
ACTIVE-PASSIVE, to which database reads/writes must go, and so on. The
same is true for oslo.db.

Nova is the only project that uses slave_connection option and it was
kind of broken: nova bare metal driver uses a separate database and
there was no way to use a slave db connection for it.

So due to lack of consistency in using of slave connection, IMO, this
should be left up to application to decide, how to use it. And we
provide EngineFacade helper already. So I'd just say, create an
EngineFacade instance for a slave connection explicitly, if you want
it to be used like it is used in Nova right now.

Thanks,
Roman

On Wed, Mar 5, 2014 at 8:35 AM, Doug Hellmann
<doug.hellmann at dreamhost.com> wrote:
>
>
>
> On Wed, Mar 5, 2014 at 10:43 AM, Alexei Kornienko
> <alexei.kornienko at gmail.com> wrote:
>>
>> Hello Darren,
>>
>> This option is removed since oslo.db will no longer manage engine objects
>> on it's own. Since it will not store engines it cannot handle query
>> dispatching.
>>
>> Every project that wan't to use slave_connection will have to implement
>> this logic (creation of the slave engine and query dispatching) on it's own.
>
>
> If we are going to have multiple projects using that feature, we will have
> to restore it to oslo.db. Just because the primary API won't manage global
> objects doesn't mean we can't have a secondary API that does.
>
> Doug
>
>
>>
>>
>> Regards,
>>
>>
>> On 03/05/2014 05:18 PM, Darren Birkett wrote:
>>
>> Hi,
>>
>> I'm wondering why in this commit:
>>
>>
>> https://github.com/openstack/oslo-incubator/commit/630d3959b9d001ca18bd2ed1cf757f2eb44a336f
>>
>> ...the slave_connection option was removed.  It seems like a useful option
>> to have, even if a lot of projects weren't yet using it.
>>
>> Darren
>>
>>
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