Mike Bayer mbayer at redhat.com
Mon Mar 9 17:26:37 UTC 2015

Clint Byrum <clint at fewbar.com> wrote:

> Excerpts from David Stanek's message of 2015-03-08 11:18:05 -0700:
>> On Sun, Mar 8, 2015 at 1:37 PM, Mike Bayer <mbayer at redhat.com> wrote:
>>> can you elaborate on your reasoning that FK constraints should be used less
>>> overall?  or do you just mean that the client side should be mirroring the
>>> same
>>> rules that would be enforced by the FKs?
>> I don't think he means that we will use them less.  Our SQL backends are
>> full of them.  What Keystone can't do is rely on them because not all
>> implementations of our backends support FKs.
> Note that they're also a huge waste of SQL performance. It's _far_ cheaper
> to scale out application servers and garbage-collect using background jobs
> like pt-archiver than it will ever be to scale out a consistent data-store
> and do every single little bit of house keeping in real time.  So even
> on SQL backends, I'd recommend just disabling and dropping FK constraints
> if you expect any more than the bare minimum usage of Keystone.

Im about -1000 on disabling foreign key constraints. Any decision based on
“performance” IMHO has to be proven with benchmarks. Foreign keys on modern
databases like MySQL and Postgresql do not add overhead to any significant
degree compared to just the workings of the Python code itself (which means,
a benchmark here should be illustrating a tangible impact on the python
application itself). OTOH, the prospect of a database with failed
referential integrity is a recipe for disaster.   

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