[SSSD] [PATCH] be_ptask: Use first/enabled_delay with backoff feature

Pavel Březina pbrezina at redhat.com
Mon Nov 24 15:57:34 UTC 2014


On 11/24/2014 04:54 PM, Lukas Slebodnik wrote:
> On (24/11/14 16:33), Michal Židek wrote:
>> On 11/24/2014 12:41 PM, Pavel Březina wrote:
>>> On 11/21/2014 03:52 PM, Michal Židek wrote:
>>>> On 11/21/2014 03:17 PM, Pavel Březina wrote:
>>>>> On 11/21/2014 03:02 PM, Michal Židek wrote:
>>>>>> On 11/21/2014 12:37 PM, Pavel Březina wrote:
>>>>>>> On 11/20/2014 07:22 PM, Michal Židek wrote:
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> it is probably not very intuitive to choose the
>>>>>>>> 'period' parameter as the initial interval in
>>>>>>>> the backoff feature (ptask). The first_delay and
>>>>>>>> enabled_delay are more suitable for this.
>>>>>>>>
>>>>>>>> See the attached patch.
>>>>>>>>
>>>>>>>> Michal
>>>>>>>
>>>>>>> I still don't think this is the best idea. Let's discuss it a little.
>>>>>>>
>>>>>>> Can you remind me what is the purpose of the backoff feature? Why
>>>>>>> was it
>>>>>>> implemented? AFAIK it was to detect when we can get back online and
>>>>>>> the
>>>>>>> randomization was added to spread the load on a server.
>>>>>>
>>>>>> We use the ptask API to check if the remote server is still offline. If
>>>>>> it is (offline), the task is rescheduled with doubled period (+random
>>>>>> offest).
>>>>>>
>>>>>>>
>>>>>>> I don't like the fact that in the current state the delay parameter is
>>>>>>> ignored if the backoff is set. And therefore all first delay, enabled
>>>>>>> delay and period (with your new patch) is ignored.
>>>>>>
>>>>>> Now I am confused a little. With the patch that I attached, the
>>>>>> enabled_delay and first_delay are respected. Only the period
>>>>>> is ignored (note that the enabled/first_delay are passed as the
>>>>>> "delay" paramter to the be_ptask_schedule).
>>>>>
>>>>> Ah, that is true. Sorry.
>>>>>
>>>>> We should not ignore the period though. Imagine that you'll use it for
>>>>> some task where first/enabled delay differs a lot from period. Or where
>>>>> first/enabled delay will be zero. We should stick to the original plan
>>>>> and double the period value.
>>>>
>>>> Ok.
>>>>
>>>> The originally designed behaviour was following:
>>>> - shedule execution
>>>> - if the task was not disabled after last execution, schedule
>>>>    next execution but double the period
>>>>
>>>> If I understand you correctly what you propose is to change it to
>>>> following:
>>>> - schedule execution (with first/enabled delay)
>>>> - if the task was not disabled after last execution:
>>>>     -schedule next execution using 'period' (if backoff_period was 0)
>>>>     -schedule next execution with doubled backoff_period
>>>
>>> Yes.
>>>
>>>> I thought it will be easier to understand the flow if we use
>>>> one initial delay in backoff and than just double it. But your
>>>> proposal makes sense. Do you want to prepare the patch or shall
>>>> I do?
>>>
>>> New patch is attached. I removed the backoff_delay field and use period
>>> directly instead. I think the flow is now pretty straight-forward and
>>> clean.
>>>
>>>>>>> If I understand the purpose of this backoff feature correctly, you
>>>>>>> want
>>>>>>> to increase the period after each execution. But in my opinion you
>>>>>>
>>>>>> Yes.
>>>>>>
>>>>>>> should still obey the first delay and enabled delay and use the
>>>>>>> *exact*
>>>>>>> times (even without the random offset IMHO).
>>>>>>
>>>>>> We should not ignore the random_offset. That would kill the purpose.
>>>>>> For example if the server goes off for less than first_delay,
>>>>>> the next "online check"  will be successful for all clients
>>>>>> (that is why the randomization is needed even in the first delay).
>>>>>> It is why the randomization was added.
>>>>>
>>>>> OK.
>>>>>
>>>>>>
>>>>>>>
>>>>>>> Attached is an *untested* patch to illustrate what I have in mind.
>>
>> The patch does not apply on current master. You probably forgot
>> to attach some previous patch where you create the private header.
>>
> It might be based on top of patches "[PATCH] tests: be_ptask"
>
> LS

Yes, sorry I did not mention that.




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