[openstack-dev] [keystone] token revocation woes

Matt Fischer matt at mattfischer.com
Thu Jul 23 16:40:48 UTC 2015


Morgan asked me to post some of my numbers here. From my staging
environment:

With 0 revocations:
Requests per second:    104.67 [#/sec] (mean)
Time per request:       191.071 [ms] (mean)

With 500 revocations:
Requests per second:    52.48 [#/sec] (mean)
Time per request:       381.103 [ms] (mean)

I have some more numbers up on my blog post about this but that's from a
virtual test environment and focused on throughput.

Thanks for the attention on this.

On Thu, Jul 23, 2015 at 8:45 AM, Lance Bragstad <lbragstad at gmail.com> wrote:

>
> On Wed, Jul 22, 2015 at 10:06 PM, Adam Young <ayoung at redhat.com> wrote:
>
>>  On 07/22/2015 05:39 PM, Adam Young wrote:
>>
>> On 07/22/2015 03:41 PM, Morgan Fainberg wrote:
>>
>> This is an indicator that the bottleneck is not the db strictly speaking,
>> but also related to the way we match. This means we need to spend some
>> serious cycles on improving both the stored record(s) for revocation events
>> and the matching algorithm.
>>
>>
>> The simplest approach to revocation checking is to do a linear search
>> through the events.  I think the old version of the code that did that is
>> in a code review, and I will pull it out.
>>
>> If we remove the tree, then the matching will have to run through each of
>> the records and see if there is a match;  the test will be linear with the
>> number of records (slightly shorter if a token is actually revoked).
>>
>>
>> This was the origianal, linear search version of the code.
>>
>>
>> https://review.openstack.org/#/c/55908/50/keystone/contrib/revoke/model.py,cm
>>
>>
>>
> What initially landed for Revocation Events was the tree-structure, right?
> We didn't land a linear approach prior to that and then switch to the tree,
> did we?
>
>>
>>
>>
>>
>>
>>
>> Sent via mobile
>>
>> On Jul 22, 2015, at 11:51, Matt Fischer <matt at mattfischer.com> wrote:
>>
>>   Dolph,
>>
>>  Per our IRC discussion, I was unable to see any performance improvement
>> here although not calling DELETE so often will reduce the number of
>> deadlocks when we're under heavy load especially given the globally
>> replicated DB we use.
>>
>>
>>
>> On Tue, Jul 21, 2015 at 5:26 PM, Dolph Mathews <dolph.mathews at gmail.com>
>> wrote:
>>
>>> Well, you might be in luck! Morgan Fainberg actually implemented an
>>> improvement that was apparently documented by Adam Young way back in
>>> March:
>>>
>>>   https://bugs.launchpad.net/keystone/+bug/1287757
>>>
>>>  There's a link to the stable/kilo backport in comment #2 - I'd be
>>> eager to hear how it performs for you!
>>>
>>> On Tue, Jul 21, 2015 at 5:58 PM, Matt Fischer <matt at mattfischer.com>
>>> wrote:
>>>
>>>>  Dolph,
>>>>
>>>>  Excuse the delayed reply, was waiting for a brilliant solution from
>>>> someone. Without one, personally I'd prefer the cronjob as it seems to be
>>>> the type of thing cron was designed for. That will be a painful change as
>>>> people now rely on this behavior so I don't know if its feasible. I will be
>>>> setting up monitoring for the revocation count and alerting me if it
>>>> crosses probably 500 or so. If the problem gets worse then I think a custom
>>>> no-op or sql driver is the next step.
>>>>
>>>>  Thanks.
>>>>
>>>>
>>>> On Wed, Jul 15, 2015 at 4:00 PM, Dolph Mathews <dolph.mathews at gmail.com
>>>> > wrote:
>>>>
>>>>>
>>>>>
>>>>> On Wed, Jul 15, 2015 at 4:51 PM, Matt Fischer <matt at mattfischer.com>
>>>>> wrote:
>>>>>
>>>>>> I'm having some issues with keystone revocation events. The bottom
>>>>>> line is that due to the way keystone handles the clean-up of these
>>>>>> events[1], having more than a few leads to:
>>>>>>
>>>>>>   - bad performance, up to 2x slower token validation with about 600
>>>>>> events based on my perf measurements.
>>>>>>  - database deadlocks, which cause API calls to fail, more likely
>>>>>> with more events it seems
>>>>>>
>>>>>>  I am seeing this behavior in code from trunk on June 11 using
>>>>>> Fernet tokens, but the token backend does not seem to make a difference.
>>>>>>
>>>>>>  Here's what happens to the db in terms of deadlock:
>>>>>> 2015-07-15 21:25:41.082 31800 TRACE keystone.common.wsgi DBDeadlock:
>>>>>> (OperationalError) (1213, 'Deadlock found when trying to get lock; try
>>>>>> restarting transaction') 'DELETE FROM revocation_event WHERE
>>>>>> revocation_event.revoked_at < %s' (datetime.datetime(2015, 7, 15, 18, 55,
>>>>>> 41, 55186),)
>>>>>>
>>>>>>  When this starts happening, I just go truncate the table, but this
>>>>>> is not ideal. If [1] is really true then the design is not great, it sounds
>>>>>> like keystone is doing a revocation event clean-up on every token
>>>>>> validation call. Reading and deleting/locking from my db cluster is not
>>>>>> something I want to do on every validate call.
>>>>>>
>>>>>
>>>>>  Unfortunately, that's *exactly* what keystone is doing. Adam and I
>>>>> had a conversation about this problem in Vancouver which directly resulted
>>>>> in opening the bug referenced on the operator list:
>>>>>
>>>>>   https://bugs.launchpad.net/keystone/+bug/1456797
>>>>>
>>>>>  Neither of us remembered the actual implemented behavior, which is
>>>>> what you've run into and Deepti verified in the bug's comments.
>>>>>
>>>>>
>>>>>>
>>>>>>  So, can I turn of token revocation for now? I didn't see an obvious
>>>>>> no-op driver.
>>>>>>
>>>>>
>>>>>  Not sure how, other than writing your own no-op driver, or perhaps
>>>>> an extended driver that doesn't try to clean the table on every read?
>>>>>
>>>>>
>>>>>>  And in the long-run can this be fixed? I'd rather do almost
>>>>>> anything else, including writing a cronjob than what happens now.
>>>>>>
>>>>>
>>>>>  If anyone has a better solution than the current one, that's also
>>>>> better than requiring a cron job on something like keystone-manage
>>>>> revocation_flush I'd love to hear it.
>>>>>
>>>>>
>>>>>>  [1] -
>>>>>> http://lists.openstack.org/pipermail/openstack-operators/2015-June/007210.html
>>>>>>
>>>>>>
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>>>>>
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