[SR-Users] Kamailio 5.0 - Better way of dealing with stateless CANCELs

[Alex Balashov]

Hi Daniel,

On 03/15/2016 04:04 AM, Daniel-Constantin Mierla wrote:

> This was discussed a lot during early days of SER and even many
> times along the 15 years so far.

I see!

Sorry, perhaps I should have dug deeper into list archives and folklore 
before suggesting it.

> The persistence of transaction is not something easy, because of its
> complex relations with timers for retransmissions over udp, but also
> with connections for tcp/tls. Each transaction has a lot of states,
> particularly bound to each outgoing branches that can be at
> different phases.

I definitely had in mind a minimalistic solution which has few 
dependencies on other elements of state -- and certainly, in my mind, it 
was implicitly UDP-only. I was thinking to just dump the current timer 
values and restore them on the assumption that the passage of time was 
"stopped" while the server was down, or, if these timers are done with 
reference to gettimeofday/wall clock time, then, on the contrary, allow 
it to elapse and dig into the timer allowance. In other words, keep it 
simple, lazy.

However, I don't know what other dependencies it would have; are 
branches not a part of TM state as well? Or is it just a question of far 
too many data structures to dump/restore?

> This is a thing of investing a lot of resources to get a solution
> for 0.01% or less, which in most of the cases sort out themselves
> fairly nice.

Fair enough. I think you're probably right on that, I just wondered if 
maybe there was a lower-hanging fruit option.

I do think you're right that the best mitigation for this problem is 
probably to have two Kamailio servers and an externally settable (i.e. 
via MI/RPC) $shv that allows one to take it "out of service", i.e. 
reject all new requests. Let the calls bleed off, then restart it.

-- Alex

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Alex Balashov | Principal | Evariste Systems LLC
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