[jdev] The future of Jabber/XMPP?

Evgeniy Khramtsov xramtsov at gmail.com
Fri Aug 27 11:58:30 CDT 2010


28.08.2010 02:36, Waqas Hussain wrote:
> Let's see.. 1M PEP nodes, with say.. 1K subscribers each. And server2
> has max 2M resources.
>
> On top, let's assume 10K different client configurations (i.e., 10K
> caps hashes).
>
> Here's what it might look like in Prosody:
>
> 1. A table of strings with all JIDs (2M resources * 3KB maximum JID
> size = 6GB maximum).
> 2. A table of local accounts mapped to list of subscriptions. Each
> subscription is just two pointers (one to a shared caps hash table,
> and one to a JID). 1M * 64 bytes = 64MB (just roughly picked 64
> bytes).
> 3. The caps hash table, mapping caps hashes to a list of +notify
> namespaces. Assume one caps hash and list takes 4KB, we have 4KB * 10K
> = 40MB (strings are shared, so this is likely a lot less).
>
> This is a simplistic view, and the string table for example is strings
> interned by Lua. I've tried to pick larger values than I actually
> expect to see in the wild (e.g., I assumed everyone has 3KB JIDs).
>
> But still, that's only a bit more than 6GB for a massive number of
> nodes and subscriptions. I could even try simulating this, and don't
> expect it to kill a server with hardware like jabber.org's.
>
> I made the assumption that there are 10K different caps hashes. Let's
> drop that now. Every resource has a unique caps hash (they are
> malicious or crazy or something). That's.. 2M * 4K = 8GB of caps data.
> The total is still under the 16GB of physical RAM jabber.org has :)
>
> Mind you, this was only a quick back of the envelope calculation :)
>    

Good point :) And now lets take a PEP message, encapsulate it in a 
multicast message with all subscribers and it will target at least one 
subscriber with very high probability. Of course, I'm not in a very 
comfortable position, because it is not so simple to count traffic, but 
nowadays I can't say if the overhead will be really great because of 
TLS-compressed links and the fact that lots of clients support PEP :)

-- 
Regards,
Evgeniy Khramtsov, ProcessOne.
xmpp:xram at jabber.ru.

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