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

[Xavi Hernandez]

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"
>      .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 ?
>
> Regards,
>
> Xavi
>
>
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