[asterisk-dev] scalability issue with realtime lastms update on qualify state change

Leandro Dardini ldardini at gmail.com
Fri Nov 15 17:52:26 CST 2013


I still have some doubts. When asterisk is bridging a simple phone call, a
rtp voice packet leaves the asterisk box every 20ms, so it is 50 packets
every second. My system has an average of 40 contemporary calls, so there
are 2000 packets leaving the box every second and asterisk can keep them
all running. I am sure the problem is what you explain, but I am not sure
the source of the problem is the one you identify.

Leandro


2013/11/16 Damon Estep <damon at soho-systems.com>

> Remember that when 1000 peers are offline there are an extra 7000 packets
> being SENT every 10s to try and reach them. Asterisk gets behind in
> processing the GOOD responses
>
>
>
> It is too busy talking to listen :)
>
>
>
> The high load starts before the network outage comes back up and gets
> worse once it comes up, here is why:
>
>
>
> The network outage in this case is a regional event, impacting 20-30% of
> users.
>
> 20-30% of users go unreachable; database is updated 400-600 times in a
> short period, no problem yet, but a higher MySQL load for a minute.
>
> 400-600 peers go into fast qualify mode with no response, 7 packets each
> every 10 seconds, no responses.
>
> Other 1400-1600 peers are engaged in normal OPTIONS dialogs, but the
> calculated RTTs(lastms) start climbing, due to the increased asterisk
> packet activity (network conditions for these peers have not changed, but
> observed lastms values progressively  increase to well over 2 seconds).
>
> Now most of the peers are beyond maxms according to asterisk, but are not
> really according to network conditions.
>
> Flapping between reachable/unreachable starts for all peers. as packets
> coming in are processed the ones that process in less than 2s are
> reachable, the rest are unreachable. Different ones every cycle.
>
> Network recovers, and nothing changes, database load is way high, peers
> will flap for hours. In one case from 3AM to 5AM before we responded and
> restarted. The network event was 15 minutes, the impact was two hours, and
> the solution was a restart.
>
> I can duplicate it on demand, but it is not very end user friendly to do
> so :(
>
>
>
> I am sure setting qualify higher (3000-5000) and modifying the hard coded
> DEFAULT_FREQ_NOTOK (from 10 to 60 or so) would also get things under
> control.
>
>
>
> Either way, I have no use for lastms in the database, so why waste cycles
> writing it?
>
>
>
> BTW, we upgraded from 1.2 to 1.8 and that is when this started. A packet
> capture during one of the events showed what was happening. 1.2 was doing
> everything the same, on the same schedules, with the same user count, but
> was not updating lastms in the DB.
>
>
>
>
>
>
>
>
>
>
>
> *From:* asterisk-dev-bounces at lists.digium.com [mailto:
> asterisk-dev-bounces at lists.digium.com] *On Behalf Of *Leandro Dardini
> *Sent:* Friday, November 15, 2013 4:10 PM
>
> *To:* Asterisk Developers Mailing List
> *Subject:* Re: [asterisk-dev] scalability issue with realtime lastms
> update on qualify state change
>
>
>
> Please read again your answer, because something is wrong ... on one side
> you are saying asterisk starts getting behind having to track the reponse
> of 7000 packets being sent every 10 seconds ... but if no answers are
> received due to network issue, is asterisk busy doing what? I don't think
> asterisk is becoming busy waiting for something not arriving. On the other
> side, you are blaming writes to the database for the slowdown. Are you
> seeing high load on the mysql database while the network is down or when
> the network is just back up?
>
>
>
> However the solution is pretty simple. Just patch chan_sip to not update
> lastms and test the system. I am pretty interested in the result.
>
>
>
> Leandro
>
>
>
> 2013/11/15 Damon Estep <damon at soho-systems.com>
>
> It is not 1000 queries in 60 seconds, it starts as 1000 MORE queries in 60
> seconds and compounds as it starts thrashing.
>
> Thousands of other queries also taking place all the time. WAY over
> 300/second total.
>
> Not DNS related, DNS is local, hostnames are IPs anyways, so no DNS needed.
>
> We have done the port 5060 block test, and can duplicate this very easily.
>
> Tables are InnoDB, binary logged, and circular replication.
>
>
>
> Remember that when 1000 peers are offline there are an extra 7000 packets
> being sent every 10s to try and reach them. Asterisk gets behind in
> processing the good responses, and the calculated RTT time for GOOD peers
> starts exceeding the maxms threshold, then the GOOD peers go offline too.
> Big snowball comes rolling down the hill and all is lost, all peers start
> flapping reachable/unreachable, and a quick restart of asterisk calms it
> down.
>
>
>
> The best confirmation that this is the issue is that it was resolved by
> patching chan_sip.c so it does not update lastms when state changes or when
> a qualify is not answered at all. Only updates on registration or
> registration expire.
>
>
>
> Still doing more testing, but pretty confident this is the answer.
>
>
>
> I understand that you are using the lastms in the realtime db for call
> routing, so my solution won't work for you. Probably need a configuration
> flag like rtupdatequalify=yes|no
>
>
>
>
>
>
>
>
>
>
>
> *From:* asterisk-dev-bounces at lists.digium.com [mailto:
> asterisk-dev-bounces at lists.digium.com] *On Behalf Of *Leandro Dardini
> *Sent:* Friday, November 15, 2013 3:47 PM
>
>
> *To:* Asterisk Developers Mailing List
> *Subject:* Re: [asterisk-dev] scalability issue with realtime lastms
> update on qualify state change
>
>
>
> My system are far less populated, so I think to be far from hitting your
> problems, but still, even after having read again your case, I can't
> believe asterisk is trashing that way. 1000 queries in 60 seconds are
> nothing compared with the load I have on the database even with far less
> peers. I had mysql databases (not voip related) running flawless with 300
> queries every second...
>
>
>
> Are you sure the trashing of your asterisk is not due to something other?
> I experienced problems with asterisk (not realtime) when the DNS servers
> were not reachable due to network outage... It will be nice to make a
> test... firewalling port 5060 inbound, so asterisk will think all peers are
> unreachable... I suspect it will not trash...
>
>
>
> Which kind of table type are you using? Are you still using MyISAM? Having
> a lots of contemporary "write" to a MyISAM table can bring a lots of
> slowdowns... just move to InnoDB.
>
>
>
> Leandro
>
>
>
> 2013/11/15 Damon Estep <damon at soho-systems.com>
>
> This is helpful, so I understand how some people are using lastms in the
> database.
>
>
>
> I also have a multiserver solution, and I use INVITE (Dial) to see if the
> peer is registered. If the user is not reachable the Dial will return a
> status from the other box that can be handled.
>
>
>
> My experience is that a multi-server solution can't scale past limits in
> the range listed below the way it works now unless you never experience a
> network issue that makes 25% or more of the peers go unreachable:
>
>
>
> 10 servers, 2000 qualified peers per server
>
> 120 second qualify interval
>
> qualify=3000
>
> default retransmit time of 1 second
>
> Database load split between two reasonably powerful MySQL servers with
> circular replication enabled
>
>
>
> at this scale, as soon as you have an event that takes down a large
> percentage of peers the database activity will back up, the qualify options
> packets will not be processed in real time, and the system will become
> unstable, with all peers flapping between reachable/unreachable, even after
> the network event is gone. It simply won't recover until you restart
> asterisk.
>
>
>
> I am sure the limits vary with environment, but there is a limit with the
> current strategy, and it is caused by excessive database updates of lastms
> during periods with high unreachable peer counts.
>
>
>
> Have you seen this yet? What is the scale of your deployment?
>
>
>
>
>
> *From:* asterisk-dev-bounces at lists.digium.com [mailto:
> asterisk-dev-bounces at lists.digium.com] *On Behalf Of *Leandro Dardini
> *Sent:* Friday, November 15, 2013 2:26 PM
> *To:* Asterisk Developers Mailing List
> *Subject:* Re: [asterisk-dev] scalability issue with realtime lastms
> update on qualify state change
>
>
>
>
> Il 15/nov/2013 22:00 "Damon Estep" <damon at soho-systems.com> ha scritto:
> >
> > peer_lastms in memory tells you that, not lastms in the realtime
> database.
> >
> > As far as I can see the lastms value in the realtime database is loaded
> only when the peer is created and quickly overwritten as soon as the first
> qualify is sent.
>
> I have a realtime multiserver solution so I need to rely on database
> lastms otherwise how can I know if a peer usually registered on the other
> server is reachable or not?
>
> Not only... on the web interface, the lastms is really pretty...
>
> >
> > On Nov 15, 2013, at 1:29 PM, "Leandro Dardini" <ldardini at gmail.com>
> wrote:
> >
> >>
> >> Il 15/nov/2013 21:11 "Damon Estep" <damon at soho-systems.com> ha scritto:
> >> >
> >> > I have run into an issue with 1.8.15 with mysql realtime peers,
> qualify=3000, and about 2000 peers.
> >> >
> >> >
> >> >
> >> > In the event of a network degradation event (high packet loss,
> network down) the system gets into an unusable state.
> >> >
> >> >
> >> >
> >> > let's say you have 2000 peers with qualify=yes (or 2000), and they
> are all reachable.
> >> >
> >> >
> >> >
> >> > Qualify frequency is 60 seconds (user definable), qualify unreachable
> is 10 seconds, and default retransmit timer of 1 second (both hardcoded in
> sip.h)
> >> >
> >> >
> >> >
> >> > 1000 peers go offline due to a network event
> >> >
> >> >
> >> >
> >> > The database has to be updated 1000 times in 60 seconds to mark the
> lastms -1 for these 1000 peers
> >> >
> >> >
> >> >
> >> > The same 1000 peers are now on a OPTIONS query schedule of once per
> 10 seconds, with 6 retransmits at 1 second intervals, total of 7 packets
> every 10 seconds for 1000 peers, or 700 new packets per second.
> >> >
> >> >
> >> >
> >> > So, we experienced a major network issue, and our response is to
> increase the load on the asterisk server dramatically by updating the
> database 1000 times and starting a new campaign to reach unreachable peers
> that are offline.
> >> >
> >> >
> >> >
> >> > In practice we see that when this happens, the calculated RTT time
> for peers that are not part of the network outage starts to increase (delay
> somewhere in hardware, code, who knows, but it does increase), and many of
> them start flapping between unreachable and reachable.
> >> >
> >> >
> >> >
> >> > The database query load goes through the roof, the number of packets
> coming out of the asterisk box goes through the roof, and asterisk will not
> recover until it is restarted, even after the network event is cleared.
> >> >
> >> >
> >> >
> >> > This is a new issue that came into play when lastms was added to the
> realtime database and the qualify code started updating it on every state
> change. 1.2 before lastms would handle this event gracefully, 1.8 wont,
> can't comment on 1.2 or 1.6.
> >> >
> >> >
> >> >
> >> > My thinking is that the lastms value in the db has little to no
> value. The only time I see it used is when a realtime peer is built from
> the database on registration. If the lastms value is -1 the peer registers
> and is set to unreachable, gets an option query and becomes reachable right
> away.
> >> >
> >> >
> >> >
> >> > rtupdate=no will stop the lastms updates, but it also stops the
> registration data from being updated in the database, which has unintended
> consequences.
> >> >
> >> >
> >> >
> >> > Also, the 10 second qualify timer when unreachable might make sense
> in small environments, but is way too aggressive for larger environments.
> It needs to be user configurable.
> >> >
> >> >
> >> >
> >> > Before I start patching, can anyone tell me what value lastms has and
> why it needs to be in the database?
> >> >
> >> >
> >>
> >> I disagree about the no value for lastms. How can I know if a peer is
> reachable without the lastms field?
> >>
> >> Leandro
> >>
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