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Hi Peter,<br>
<br>
<br>
Sounds like a useful feature. Indeed 5 seconds is immediate for
normal presence (availability status)and we shouldn't require more
frequent notifications. Klaus was talking about 'dialog' event where
this feature is actually not useful as the status changes quite
fast. <br>
<br>
More than this, as you mentioned, having a special notifier process
will also solve the problem of bad cseq due to concurrency, so even
the more useful.<br>
<br>
From what I understand this solution will work only if using DB_ONLY
mode. WRITE_THROUGH mode is actually useless if this feature is
used(as it was actually helping not to query the active_watchers
table for sending notifies) . This should be kept in mind and
mentioned in the documentation.<br>
<br>
<br>
On 03/30/2012 03:10 PM, Peter Dunkley wrote:
<blockquote cite="mid:1333109441.2773.33.camel@pd-laptop-linux"
type="cite">
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Hi,<br>
<br>
With further thinking I'd like to do something along these lines:<br>
- Leave the presentity table and handling alone.<br>
- When a new modparam (notifier_poll_rate) is non zero set a flag
(with value based on a hash of the Call-ID of the dialog) in the
dialog indicating a NOTIFY is required (either for all watchers of
a presentity after a PUBLISH, or just one dialog after a
SUBSCRIBE), but do not send NOTIFY requests immediately.<br>
- Have a notifier process (running on a timer as per my last
change to RLS) that checks for dialogs needing updated (a subset
each time it is run based on flag value) and sends NOTIFY
requests.<br>
- Each time the notifier runs 1/(waitn_time * notifier_poll_rate)
of the dialogs is checked. waitn_time is another new modparam.<br>
- Sensible values of notifier_poll_rate and waitn_time are 10 and
5 (default) respectively. This means the notifier checks for work
10 times a second, and NOTIFY requests take at most 5 seconds to
be sent. The default for notifier_poll_rate will be 0 which means
use the existing behaviour.<br>
<br>
I will need to make sure that, when in DB only mode and with the
notifier enabled, I do not retrieve the dialogs when doing the
immediate processing of a PUBLISH. Simply doing an update() on
the flags and checking affected_rows() (if available) should be
enough. Similarly, when I receive a SUBSCRIBE I should update the
remote CSeq and the flags at the same time, and I can use
affected_rows() (if available) to confirm the dialog exists and
send the right response. This should minimise the DB impact of
this change.<br>
</blockquote>
<br>
Indeed, no need to query the active_watchers table from anywhere
else except the notifier process. And actually, when Publish is
received you don't even need to know if there were rows to update or
not. <br>
<br>
The solution sounds very good to me.<br>
<br>
Good luck on implementing it and thanks for sharing :) .<br>
<br>
Regards,<br>
Anca<br>
<br>
<br>
<blockquote cite="mid:1333109441.2773.33.camel@pd-laptop-linux"
type="cite">
<br>
This should have the effect of maintaining the existing behaviour
for those who need/want it, evening out the sending of NOTIFY
requests as much as possible, ensuring a NOTIFY is always sent in
a timely fashion (within 5 seconds should count as immediate for a
NOTIFY after a SUBSCRIBE).<br>
<br>
Once this works with a single notifier process it should be quite
simple to extend it to having a pool of notifier processes if that
is required.<br>
<br>
How does this sound?<br>
<br>
Regards,<br>
<br>
Peter<br>
<br>
<br>
On Fri, 2012-03-30 at 09:26 +0100, Peter Dunkley wrote:<br>
<blockquote type="CITE"> Hi,<br>
<br>
When running a soak on presence with RLS NOTIFY requests are by
far the most common. Further, especially with RLS in place,
performance of Kamailio presence can be quite limited. The
writers of the presence RFCs do seem to acknowledge that this is
indeed an issue - hence the restrictions on the rate at which
NOTIFY requests can be sent.<br>
<br>
I am looking for ways to sensibly reduce the number of NOTIFYs
generated, and in this case, it seems that the presence module
is actually sending them more frequently than the specification
says it should anyway.<br>
<br>
Reducing the number of NOTIFYs sent doesn't just help with
presence, but it should also reduce the amount of work that the
RLS module has to do too - as it will receive (and have to
process) less NOTIFYs as well.<br>
<br>
Of course I am open to other ways to approach this problem.
Another thing I have been considering is setting the flags and
fields I have discussed below but not sending NOTIFYs right away
at all. I would then have a timer task (perhaps at the 100ms
you suggest below) that generates outstanding NOTIFYs - but not
at a rate of more than once per five seconds for each
presentity. Effectively, this timer task would be a notifier,
which I think is one of the things suggested recently on the
list.<br>
<br>
Regards,<br>
<br>
Peter<br>
<br>
On Fri, 2012-03-30 at 10:01 +0200, Klaus Darilion wrote:
<blockquote type="CITE">
<pre>
On 29.03.2012 23:19, Peter Dunkley wrote:
> Hi,
>
> RFC 3856 section 6.10 states: "A PA SHOULD NOT generate notifications for
> a single presentity at a rate of more than once every five seconds."
I wonder if this is useful. E.g. a user tries to call somebody, but the
target is busy. Thus, the call will last maybe 3 seconds having the
dialog states: trying, proceeding, early, terminated.
How is it supposed to work? It just sends trying, but no the others? Or
will they be queued, so only trying, and 5 seconds later, terminated is
sent?
</pre>
</blockquote>
I don't understand what this has to do with calls. I am just
talking about NOTIFY requests from presence after a change in
presentity or a SUBSCRIBE.<br>
<br>
<blockquote type="CITE">
<pre>>
> I would like to add this to the presence module (making the rate
> configurable).
>
> I have an idea as to how I would like to do it:
> - Add a last notified time-stamp field to each presentity
> - Add a updated since last notified flag field to each presentity
> - Add a notify required flag field to each active_watcher
>
> - When a presentity is updated the last notified time-stamp is checked.
> If the time is far enough in the past the notifies are sent and the
> time-stamp is updated. If enough time has not passed the updated since
> flag is set for the presentity and the notify required flag is set for all
> active_watchers of that presentity.
> - When a presentity is subscribed to (this includes re-subscribes) the
> last notified time-stamp is checked. If the time is far enough in the
> past the (single) notify is sent and the time-stamp is updated. If enough
> time has not passed the updated since flag is set for the presentity and
> the notify required flag is set for this active_watcher record.
RFC3265 states that a NOTIFY MUST sent immediately after every SUBSCRIBE.
</pre>
</blockquote>
Ah... But define immediately. A 2XX response should also be
sent immediately after every SUBSCRIBE, but the timeout is 64*T1
(32 seconds). So a NOTIFY that, in many cases, comes out right
away, or in the worst case within 5 to 10 seconds, should count
as immediate.<br>
<br>
<blockquote type="CITE">
<pre>> - A timer (the minimum time between subscribes - default 5 seconds) is
> run. On expiry a query is done on the presentity table for presentities
> that have been updated _AND_ the last notified time is more than the
> minimum time ago. For each of these presentities, a query is done on the
> active_watchers for watchers of that presentity that have the notify
> required flag set. Notifies containing the presentities are then sent to
> the watchers waiting on them.
>
> This should ensure that no presentity notifies more than it should, while
> ensuring that all changes are (eventually) sent out, and all subscribes
> result in a notify (eventually) being sent. Eventually being typically
> within 5 seconds and in under 10 seconds in the worst case (assuming the
> default setting of 5 seconds).
>
> Can anyone see any problems with this?
I wonder why you delay NOTIFYs for (re)SUBSCRIBEs? On (re)SUBSCRIBEs
just NOTIFY with last published state and do not set the "notify
required" flag. Then it may happen that the minimum NOTIFY interval is
not maintained the first few seconds after a (re)SUBSCRIBE but IMO this
is not that bad and enables immediate notification after every
(re)SUBSCRIBE.
</pre>
</blockquote>
As you say, if I receive a PUBLISH and then a re-SUBSCRIBE to a
presentity then I will send out NOTIFYs too often. I have seen
(bad) clients that re-PUBLISH immediately before re-SUBSCRIBE
and un-PUBLISH immediately before un-SUBSCRIBE. If a lot of
people use these bad clients then you have a problem.<br>
<br>
<blockquote type="CITE">
<pre>> Are there any objections to me implementing this?
Make it configurable :-) E.g. setting "minimum_notification_delay" to 0
disables the feature.
</pre>
</blockquote>
Of course <img src="cid:part1.00050002.03090404@1and1.ro"
alt=":-)" align="middle" border="0"><br>
<br>
<blockquote type="CITE">
<pre>It may also increase DB load and cause more race-conditions (to be
resolved with DB-transactions) due to more DB lookups.
</pre>
</blockquote>
It also helps with a race condition I think I am seeing (and
similar to that recently discussed on this list) where you can
have more than one NOTIFY outstanding on a dialog at a time, and
if these get out of sequence then you do definitely get
problems.<br>
<br>
While there may be more DB load overall, I suspect that because
this helps spread it out somewhat it should make the performance
more even. Also many of these queries will be much simpler and
lighter as I do not need to always retrieve the presentity
field, which is particularly large.<br>
<br>
<blockquote type="CITE">
<pre>E.g. what if the timer finds a presentity for which NOTIFYs needs to be
sent and - while iterating over all the presentities - a new PUBLISH is
received which triggers immediate NOTIFY. It may happen that both
processes manipulate the active watchers table at the same time (notify
required flag).
</pre>
</blockquote>
Is this not also a problem with rls_presentity which uses a very
similar mechanism already?<br>
<br>
<blockquote type="CITE">
<pre>
> In theory running a (5 second) timer could make presence "lumpy" in the
> same way RLS is (see my previous email). However, if this proves to be
> the case I believe the same mechanism I have proposed for RLS can be used
> here.
Why run the timer only every 5 seconds? Run it every second (or 100ms)
then it should not be lumpy anymore.
</pre>
</blockquote>
<br>
<blockquote type="CITE">
<pre>regards
Klaus
</pre>
</blockquote>
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</pre>
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<pre>--
Peter Dunkley
Technical Director
Crocodile RCS Ltd
</pre>
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