[openstack-dev] [Glance] Replacing Glance DB code to Oslo DB code.

Jay Pipes jaypipes at gmail.com
Sun Aug 18 22:47:28 UTC 2013

On 08/18/2013 06:28 PM, Joe Gordon wrote:
> On Aug 18, 2013 3:58 PM, "Jay Pipes" <jaypipes at gmail.com
> <mailto:jaypipes at gmail.com>> wrote:
>  >
>  > On 08/18/2013 03:53 AM, Joshua Harlow wrote:
>  >>
>  >> I always just liked SQL as the database abstraction layer ;)
>  >>
>  >> On a more serious note I think novas new object model might be a way
> to go but in all honesty there won't be a one size fits all solution. I
> just don't think sqlalchemy is that solution personally (maybe if we
> just use sqlalchemy core it will be better and eject just the orm layer).
>  >
>  >
>  > What is specifically wrong with SQLAlchemy's ORM layer? What would
> you replace it with? Why would use SQLAlchemy's "core" be better?
>  >
>  > I've seen little evidence that SQLAlchemy's ORM layer is the cause
> for database performance problems. Rather, I've found that the database
> schemas in use -- and in some cases, the *way* that the SQLAlchemy ORM
> is called (for example, doing correlated subqueries instead of straight
> joins) -- are primary causes for database performance issues.
>  From what I have seen the issue is both the queries and the ORM layer.
> See https://bugs.launchpad.net/nova/+bug/1212418  for details.

Good point.

For the record, I'm not a fan of lazy/eager loading of relations in the 
models themselves, but instead always being explicit about the exact 
data you wish to query for.

It's similar in nature to the SQL best practice of never doing SELECT * 
FROM <set> and instead of always being explicity about the columns you 
wish to retrieve...


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