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

[Xavi Hernandez]

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 ?


>
>>>>> 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
>
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