[SR-Users] Dialog Module Hash Size vs Number of Dialogs
Daniel-Constantin Mierla
miconda at gmail.com
Mon Dec 4 20:56:17 CET 2017
The hash_size has no relevance on how many dialogs can be handled. It is
only related to the lookup performance. So even with hash_size=1 you can
have same number of dialogs as with hash_size=4096 or higher.
The difference is that with hash_size=1, all the dialogs are in a single
linked list, so if you have 2000 active dialog, you may have the worse
case that it requires 2000 matching operations to lookup a specific dialog.
If the hash_size is 2048, the at 2000 active calls and a fair
distribution, then looking up a specific dialog will be done in a single
matching operation. Fair distribution cannot be ensure, but it is quite
good, so typically the difference between the list loaded slot and most
loaded slot is not that high. I expect that worse case situation won't
require more that 5 matching operations on a hash table with 2048 slots
when having 2000 active calls.
To put limit on active calls, the simplest solution is to do a test on
$stat(active_dialogs)>=limit then reject the initial invite:
-
https://www.kamailio.org/docs/modules/stable/modules/dialog.html#idp34022668
You may need statistics module to get the $stat(...) var:
- https://www.kamailio.org/docs/modules/stable/modules/statistics.html
The alternative would be to set all active calls in a single dialog profile.
-
https://www.kamailio.org/docs/modules/stable/modules/dialog.html#dialog.f.set_dlg_profile
Then get the size of the profile and test it against the limit.
This is more suitable if you want to set limits per user, a.s.o.,
because you can group on profiles with a specific key (e.g., username).
Cheers,
Daniel
On 04.12.17 19:28, Mark Blackford wrote:
> Thank you for your response!
>
> I am currently replacing the call_control module used with CDRTool
> Prepaid with the dialog module using hash tables. The speed and
> stability are tremendously better!
>
> My concern is two-fold:
> 1) I do not want calls to be blocked because I set the hash table size
> too small.
> 2) I do not want any memory usage problems that could cause kamailio
> stability issues.
>
> My understanding, or at least how I want to use the "hash_size"
> modparam, is that hash_size gives dialog a set memory space (aka slots
> and buckets) to store the dialogs being tracked. This is great since
> I "think" I will have constant memory consumption that will be a fixed
> amount and never "grow". However, I wanted to get a rough idea of how
> many dialogs (customer calls) I could track per kamailio instance to
> properly choose the hash size.
>
> I thought it would be easy to set the value to something very small in
> the lab and just run up the number of calls until kamailio hits an
> upper limit and fails to create any more dialogs.
> modparam("dialog", "hash_size", 32)
>
> However, I am able to create almost 2000 dialogs no matter what size I
> choose. After, reading the information in the link about hash tables
> and your response, I see how a larger table with more "hashing"
> increases lookup performance, but I still do not see how the total
> number of dialogs that the module tracks can be set so that the
> kamailio memory usage is protected. I still look at the hash_size as
> the key here and that there should be a relationship, perhaps rough at
> best, to the maximum number of dialogs supported in the table.
>
> Thanks so much for your time,
> Mark Blackord
> Digium Cloud Services
>
> On Sat, Dec 2, 2017 at 2:50 AM, Daniel-Constantin Mierla
> <miconda at gmail.com <mailto:miconda at gmail.com>> wrote:
>
> Hello,
>
> hash size does not set any limitation to the number of dialogs
> (active calls), it has impact on searching the dialogs, so if you
> have a lot of active calls, increasing the hash size might improve
> performances. Effectively the hash size is used to compute the
> number of slots (aka buckets) the hash table is going to have, see
> more technical details about hash tables at:
>
> - https://en.wikipedia.org/wiki/Hash_table
> <https://en.wikipedia.org/wiki/Hash_table>
>
> Can you elaborate on your statement:
>
> > but even setting the hash size to a very tiny number does stop me from creating hundreds of dialogs
>
> Do you mean you are not able to create as many dialogs as you want?
>
> Cheers,
> Daniel
>
>
> On 01.12.17 19:54, Mark Blackford wrote:
>> Hello,
>>
>> I am trying to properly size the use of the Dialog Module hash
>> for our implementation using:
>>
>> modparam("dialog", "hash_size", <number that is power of two>)
>>
>> However, in my testing, I have been unable to figure out the
>> relationship between the hash size and a number of dialogs I need
>> to support. I think the hash size is specifying a memory block
>> in kB, but even setting the hash size to a very tiny number does
>> stop me from creating hundreds of dialogs.
>>
>> Is there a way to determine a relationship between the hash size
>> and a rough number of dialogs that would be expected?
>>
>> An example of a a dialog looks like this from kamctl:
>>
>> [root at kamailio01 ~]# kamctl dialog show
>> dialog memory records
>> dialog:: hash=22:70
>> state:: 4
>> ref_count:: 2
>> timestart:: 1512151205
>> timeout:: 36083666
>> callid::
>> 0gQAAC8WAAACBAAALxYAAClws2wyL8GE+CSgRY7HIhmg9ZUIISZad46ntOPng3iPIcLaxzLFaytRTI7M0Bzz0g-- at 10.155.8.40
>> <mailto:0gQAAC8WAAACBAAALxYAAClws2wyL8GE%2BCSgRY7HIhmg9ZUIISZad46ntOPng3iPIcLaxzLFaytRTI7M0Bzz0g-- at 10.155.8.40>
>> from_uri::
>> sip:b53667d44239457fbc94fc2f4c4e25a6 at sip.dcs-staging.net
>> <mailto:sip%3Ab53667d44239457fbc94fc2f4c4e25a6 at sip.dcs-staging.net>
>> from_tag:: 10.155.8.40+1+689d7e5e+8fcf481a
>> caller_contact::
>> sip:43f0ae1480846185e8803f21e9f2b721 at 10.155.8.40:5060;transport=udp
>> caller_cseq:: 24115
>> caller_route_set::
>> caller_bind_addr:: udp:10.155.8.11:5060 <http://10.155.8.11:5060>
>> callee_bind_addr:: udp:10.155.8.11:5060 <http://10.155.8.11:5060>
>> to_uri:: sip:2052773090 at sip.dcs-staging.net
>> <mailto:sip%3A2052773090 at sip.dcs-staging.net>
>> to_tag:: sip+1+bdcd0004+2038f37c
>> callee_contact::
>> sip:ca2013e84f10348a1cc825c12562bde7 at 10.155.8.40:5060;transport=udp
>> callee_cseq:: 0
>> callee_route_set::
>>
>>
>>
>> Thanks!
>> --
>> Mark Blackford
>> Digium Cloud Services
>> 678.230.8769
>>
>>
>>
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>
> --
> Daniel-Constantin Mierla
> www.twitter.com/miconda <http://www.twitter.com/miconda> -- www.linkedin.com/in/miconda <http://www.linkedin.com/in/miconda>
> Kamailio Advanced Training - www.asipto.com <http://www.asipto.com>
> Kamailio World Conference - May 14-16, 2018 - www.kamailioworld.com <http://www.kamailioworld.com>
>
>
>
>
> --
> Mark Blackford
> Digium Cloud Services
> 678.230.8769
>
--
Daniel-Constantin Mierla
www.twitter.com/miconda -- www.linkedin.com/in/miconda
Kamailio Advanced Training - www.asipto.com
Kamailio World Conference - May 14-16, 2018 - www.kamailioworld.com
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