[Serusers] Why Transactional Accounting?
Andrew Fullford
akfullfo at august.com
Thu Aug 12 20:17:57 CEST 2004
A good alternative with postgres for external actions that might incur
large delays is to use a trigger that simply touches a file in the file
system. A very low-overhead program can watch for a change in the file
timestamp and perform an action. This watcher program can check the
file on a few seconds delay giving much better responsiveness than is
typical of cron or database job scheduling, and the workload on the
database only runs as needed, not every minute.
This also has the advantage (or disadvantage) of transferring the
action to a different security and execution realm. Ie, the operation
now runs as the uid of the watcher program and with the watcher
program's permissions, scheduler-priority, and enviroment, rather than
as the postgres user.
However, as Greg mentioned, we have implemented the code to match
INVITE to BYE. This has not had substantantial stress testing but
certainly operates with no measurable load at >20 calls per minute.
Matching performance is not an issue even with six-figure call
histories. Good indexing completely resolves this for probably any
size, but almost certainly for eight-figure sizes. That's because you
are only ever concerned with the currently active set of calls (those
with no hangup time recorded yet).
The two biggest problems we have encountered are:
BYEs are not reliable. They are initiated solely by the UA, so
even with a completely reliable network, BYEs will go missing
if the user powers down or disconnects their system before
hanging up.
call_ids are not reliable. They are also created by the UA,
and UAs have bugs. Even major vendors have released firmware
that does not produce unique call_ids.
For the most part, these problems can be banged on until they go away.
For the former you could do probing from the proxy to confirm calls are
still in progress. This is still a problem. What if the UA simply
ignores the probe? Then the proxy fakes a BYE to close the call but
the call (the RTP path) is still operating and the caller is now
talking for free. Instead, we use multiple accounting sources for
calls we are actually billing for and for SIP<->SIP we just ignore the
problem because we're not billing that path.
The latter can be resolved using internally generated IDs among a realm
of cooperating proxies, but this is an impossible dream in any mixed
vendor world, and implies all SIP routing must be done through the
realm, which may also be undesirable or unattainable.
Currently we use call_id/fromtag/totag as a key which seems reliable
for most UA vendors and is consistent with the RFC. We also detect
attempts to reuse keys. Currently these are just logged but they will
probably eventually trigger call rejection and might even get to UA mfg
+ firmware version blocking if we start to encounter widespread flaws.
The objective of the latter is to get the manufacturer to take notice.
Andrew Fullford
--
Email: andy at addabrand.com
Web: www.addabrand.com
> Cc: <mikep at pch.net> <mikep at pch.net>,
> Michael Shuler <mike at bwsys.net>,
> 'serusers at lists.iptel.org' <serusers at lists.iptel.org>,
> 'Addabrand Support' <support at addabrand.com>
> From: Greg Fausak <greg at addabrand.com>
> Subject: Re: [Serusers] Why Transactional Accounting?
> Date: Thu, 12 Aug 2004 09:27:41 -0500
> To: "Arne Scheffer" <arne.scheffer at ritstele.com>
>
> Hi Guys,
>
> <soapbox>
> OK, I have to say that I am opinionated about databases. I've been
> working with databases since before Oracle (I actually worked at
> Britton Lee in Los Gatos California, they manufactured a database
> machine).
> Anyway...
>
> Postgres is a serious database engine. When we first starting using
> SER I wrote the postgres backend because it had many characteristics
> that I prefer over the then available mysql engine. I have written
> large
> scale database applications, and I have had the opportunity to
> port applications that were melting on mysql to postgres.
>
> Most databases are administration heavy, postgres is no exception.
> They must be indexed, profiled, analyzed and vacuumed to maintain good
> performance.
>
> For this application, we use:
>
> syslog pushing accounting information to various capturing syslogd's.
> A sweeper that reaps syslog information and populates the postgres
> database.
>
> The customer's call information is live and viewable up to the 6 second
> mark.
> Call INVITE/BYE matcher only has to deal with 'current call' records,
> that is, those
> that haven't been matched. Now, granted, we haven't had a real big
> load (yet), so
> I don't know if it will scale. But, I believe it will.
>
> We don't use triggers either. I think they would work fine but
> they make ad-hoc database changes a bit harder.
> </soapbox>
>
> ---greg
>
>
>
> On Aug 12, 2004, at 2:52 AM, Arne Scheffer wrote:
>
> > Mike,
> >
> > In a high load situation I would not use a trigger. From experience
> > you can encounter big billing delays when you start using complex
> > billing. Most DB's see the trigger as part of your insert action and
> > will not reply to the application that performed the INSERT until the
> > trigger has finished. This means your SER may have to wait for a few
> > seconds to know if the insert was OK (serious performance impact).
> >
> > Now may say a few seconds why ?
> > just take into account you have a number port database with 2M records
> > which you need to scan to see if the number is ported. Can take a
> > second very easily :(
> >
> > I would advise using a JOB on your SQL server (supported by Oracle &
> > MSSQL, Postgres does not support it I think) which runs every minute.
> > You still have the load on the server but SER will not be delayed by
> > TRIGGER.
> >
> > Arne.
> >
> >
> >
> > -----Original Message-----
> > From: serusers-bounces at iptel.org [mailto:serusers-bounces at lists.iptel.org]On
> > Behalf Of Michael Przybylski
> > Sent: donderdag 12 augustus 2004 8:32
> > To: Michael Shuler
> > Cc: serusers at lists.iptel.org
> > Subject: Re: [Serusers] Why Transactional Accounting?
> >
> >
> > SER seems to support postgresql as an accounting backend, and
> > postgresql
> > support "triggers."
> >
> > This is a synthesis of only a cursory look at the SER source tree and
> > postgresql docs on triggers, but it looks like you can do the
> > following:
> >
> > 1.) Set up SER to use postgresql as it's accounting backend.
> > 2.) Create an extra table with the fields you would like to see in your
> > "real world records."
> > 3.) Create trigger to corelate INVITES and BYEs and insert a row into
> > your
> > "real world records" table every time it notices that a BYE has been
> > inserted into the transactional accounting table.
> >
> > This is still extra CPU load that will hurt your scalability but it's
> > fairly elegant and an experienced PostgreSQL user/admin should be able
> > to
> > crate it up pretty quickly.
> >
> > Finally, I'd bet that a 2-way or 4-way opteron-based database server
> > would
> > hold up to a pretty substantial call volume, even while running that
> > trigger.
> >
> > Best regards,
> > Mike Przybylski
> >
> > On Thu, 12 Aug 2004, Michael Shuler wrote:
> >
> >> At first it seemed like a really good idea then the more I looked at
> >> real
> >> world records I realized that to generate a bill for a customer would
> >> require quite bit of work on MySQL's part to match up the INVITE's
> >> and the
> >> BYE's and then calc the difference in the times. This causes a bit
> >> of a
> >> problem for me because I like my customers to be able to see their CDR
> >> records live. Which really isn't much unless you look at it from a
> >> 100,000
> >> user perspective. I would either have to beat up my SQL server every
> >> time
> >> they look at their records (or my customer service employees look at
> >> them or
> >> even when the biller generates their bill) or run a cron job that
> >> runs every
> >> so often to convert the data to a single record with a start time and
> >> a
> >> duration and store it in another table. The cron idea isn't too
> >> efficient
> >> because of wasting disk space and rewriting a lot of the same data
> >> twice.
> >>
> >> This then leads me to ask why the SER acc module wasn't setup to
> >> generate an
> >> initial start record identical to the INVITE message that it already
> >> does
> >> that would be marked as "in progress"? Then when a BYE is received
> >> with a
> >> matching Call-ID you find the original INVITE record, change its
> >> status to
> >> "done" and populate a duration field. Any ideas why this can't be
> >> done
> >> without affecting SER's scalability? :)
> >>
> >> Thanks!
> >>
> >> ----------------------------------------
> >>
> >> Michael Shuler, C.E.O.
> >> BitWise Systems, Inc.
> >> 682 High Point Lane
> >> East Peoria, IL 61611
> >> Office: (217) 585-0357
> >> Cell: (309) 657-6365
> >> Fax: (309) 213-3500
> >> E-Mail: mike at bwsys.net
> >> Customer Service: (877) 976-0711
> >>
> >> _______________________________________________
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> >>
> >
> >
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> >
> Greg Fausak
> www.AddaBrand.com
> (US) 469-546-1265
>
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