[Gluster-devel] Should we enable contention notification by default ?

[Xavi Hernandez]

On Thu, May 2, 2019 at 5:45 PM Atin Mukherjee <atin.mukherjee83 at gmail.com>
wrote:

>
>
> On Thu, 2 May 2019 at 20:38, Xavi Hernandez <xhernandez at redhat.com> wrote:
>
>> On Thu, May 2, 2019 at 4:06 PM Atin Mukherjee <atin.mukherjee83 at gmail.com>
>> wrote:
>>
>>>
>>>
>>> On Thu, 2 May 2019 at 19:14, Xavi Hernandez <xhernandez at redhat.com>
>>> wrote:
>>>
>>>> On Thu, 2 May 2019, 15:37 Milind Changire, <mchangir at redhat.com> wrote:
>>>>
>>>>> On Thu, May 2, 2019 at 6:44 PM Xavi Hernandez <xhernandez at redhat.com>
>>>>> wrote:
>>>>>
>>>>>> Hi Ashish,
>>>>>>
>>>>>> On Thu, May 2, 2019 at 2:17 PM Ashish Pandey <aspandey at redhat.com>
>>>>>> wrote:
>>>>>>
>>>>>>> Xavi,
>>>>>>>
>>>>>>> I would like to keep this option (features.lock-notify-contention)
>>>>>>> enabled by default.
>>>>>>> However, I can see that there is one more option which will impact
>>>>>>> the working of this option which is "notify-contention-delay"
>>>>>>>
>>>>>>
>>>>> Just a nit. I wish the option was called "notify-contention-interval"
>>>>> The "delay" part doesn't really emphasize where the delay would be put
>>>>> in.
>>>>>
>>>>
>>>> It makes sense. Maybe we can also rename it or add a second name
>>>> (alias). If there are no objections, I will send a patch with the change.
>>>>
>>>> Xavi
>>>>
>>>>
>>>>>
>>>>>>      .description = "This value determines the minimum amount of time
>>>>>>> "
>>>>>>>                     "(in seconds) between upcall contention
>>>>>>> notifications "
>>>>>>>                     "on the same inode. If multiple lock requests
>>>>>>> are "
>>>>>>>                     "received during this period, only one upcall
>>>>>>> will "
>>>>>>>                     "be sent."},
>>>>>>>
>>>>>>> I am not sure what should be the best value for this option if we
>>>>>>> want to keep features.lock-notify-contention ON by default?
>>>>>>> It looks like if we keep the value of notify-contention-delay more,
>>>>>>> say 5 sec, it will wait for this much time to send up call
>>>>>>> notification which does not look good.
>>>>>>>
>>>>>>
>>>>>> No, the first notification is sent immediately. What this option does
>>>>>> is to define the minimum interval between notifications. This interval is
>>>>>> per lock. This is done to avoid storms of notifications if many requests
>>>>>> come referencing the same lock.
>>>>>>
>>>>>> Is my understanding correct?
>>>>>>> What will be impact of this value and what should be the default
>>>>>>> value of this option?
>>>>>>>
>>>>>>
>>>>>> I think the current default value of 5 seconds seems good enough. If
>>>>>> there are many bricks, each brick could send a notification per lock. 1000
>>>>>> bricks would mean a client would receive 1000 notifications every 5
>>>>>> seconds. It doesn't seem too much, but in those cases 10, and considering
>>>>>> we could have other locks, maybe a higher value could be better.
>>>>>>
>>>>>> Xavi
>>>>>>
>>>>>>
>>>>>>>
>>>>>>> ---
>>>>>>> Ashish
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> ------------------------------
>>>>>>> *From: *"Xavi Hernandez" <xhernandez at redhat.com>
>>>>>>> *To: *"gluster-devel" <gluster-devel at gluster.org>
>>>>>>> *Cc: *"Pranith Kumar Karampuri" <pkarampu at redhat.com>, "Ashish
>>>>>>> Pandey" <aspandey at redhat.com>, "Amar Tumballi" <atumball at redhat.com>
>>>>>>> *Sent: *Thursday, May 2, 2019 4:15:38 PM
>>>>>>> *Subject: *Should we enable contention notification by default ?
>>>>>>>
>>>>>>> Hi all,
>>>>>>>
>>>>>>> there's a feature in the locks xlator that sends a notification to
>>>>>>> current owner of a lock when another client tries to acquire the same lock.
>>>>>>> This way the current owner is made aware of the contention and can release
>>>>>>> the lock as soon as possible to allow the other client to proceed.
>>>>>>>
>>>>>>> This is specially useful when eager-locking is used and multiple
>>>>>>> clients access the same files and directories. Currently both replicated
>>>>>>> and dispersed volumes use eager-locking and can use contention notification
>>>>>>> to force an early release of the lock.
>>>>>>>
>>>>>>> Eager-locking reduces the number of network requests required for
>>>>>>> each operation, improving performance, but could add delays to other
>>>>>>> clients while it keeps the inode or entry locked. With the contention
>>>>>>> notification feature we avoid this delay, so we get the best performance
>>>>>>> with minimal issues in multiclient environments.
>>>>>>>
>>>>>>> Currently the contention notification feature is controlled by the
>>>>>>> 'features.lock-notify-contention' option and it's disabled by default.
>>>>>>> Should we enable it by default ?
>>>>>>>
>>>>>>> I don't see any reason to keep it disabled by default. Does anyone
>>>>>>> foresee any problem ?
>>>>>>>
>>>>>>
>>> Is it a server only option? Otherwise it will break backward
>>> compatibility if we rename the key, If alias can get this fixed, that’s a
>>> better choice but I’m not sure if it solves all the problems.
>>>
>>
>> It's a server side option. I though that an alias didn't have any other
>> implication than accept two names for the same option. Is there anything
>> else I need to consider ?
>>
>
> If it’s a server side option then there’s no challenge in alias. If you do
> rename then in heterogeneous server versions volume set wouldn’t work
> though.
>

I created a patch to change this and set notify-contention to 'yes' by
default. I'll test upgrade paths to make sure that nothing breaks.

Xavi


>
>>
>>>
>>>>>>> Regards,
>>>>>>>
>>>>>>> Xavi
>>>>>>>
>>>>>>> _______________________________________________
>>>>>> Gluster-devel mailing list
>>>>>> Gluster-devel at gluster.org
>>>>>> https://lists.gluster.org/mailman/listinfo/gluster-devel
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Milind
>>>>>
>>>>> _______________________________________________
>>>> Gluster-devel mailing list
>>>> Gluster-devel at gluster.org
>>>> https://lists.gluster.org/mailman/listinfo/gluster-devel
>>>
>>> --
>>> --Atin
>>>
>> --
> --Atin
>
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