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

Pavel Březina pbrezina at redhat.com
Fri Nov 21 14:17:18 UTC 2014


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.

>> 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.
>>
>>
>
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