15 Mar
2016
15 Mar
'16
4:16 a.m.
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
--
Alex Balashov | Principal | Evariste Systems LLC
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