[sr-dev] presence module makes excessive cleanups when subs_db_mode=3

[Andrew Pogrebennyk]

Hi,
when presence module is running with subs_db_mode=3 it makes an
excessive number of SQL select queries, litelly dozens per second:
> 		25232 Query	select presentity_uri,callid,to_tag,from_tag,event from active_watchers where updated=64 AND event<>'presence.winfo'
> 		25233 Query	select presentity_uri,callid,to_tag,from_tag,event from active_watchers where updated=116 AND event<>'presence.winfo'
> 		25233 Query	select presentity_uri,callid,to_tag,from_tag,event from active_watchers where updated=116 AND event='presence.winfo'
> 		25232 Query	select presentity_uri,callid,to_tag,from_tag,event from active_watchers where updated=64 AND event='presence.winfo'
> 		25231 Query	select presentity_uri,callid,to_tag,from_tag,event from active_watchers where updated=14 AND event<>'presence.winfo'
> 		25231 Query	select presentity_uri,callid,to_tag,from_tag,event from active_watchers where updated=14 AND event='presence.winfo'
> 		25233 Query	select presentity_uri,callid,to_tag,from_tag,event from active_watchers where updated=118 AND event<>'presence.winfo'
> 		25232 Query	select presentity_uri,callid,to_tag,from_tag,event from active_watchers where updated=66 AND event<>'presence.winfo'
> 		25233 Query	select presentity_uri,callid,to_tag,from_tag,event from active_watchers where updated=118 AND event='presence.winfo'
> 		25232 Query	select presentity_uri,callid,to_tag,from_tag,event from active_watchers where updated=66 AND event='presence.winfo'
> 		25231 Query	select presentity_uri,callid,to_tag,from_tag,event from active_watchers where updated=16 AND event<>'presence.winfo'
> 		25231 Query	select presentity_uri,callid,to_tag,from_tag,event from active_watchers where updated=16 AND event='presence.winfo'

Steps to reproduce: registers two subscribers in jitsi and add them to
contact lists of each other.
The kamailio version is 3.3.2. I'm not doing anything special
configuration-wise:

loadmodule "presence.so"
modparam("presence", "db_url", "mysql://kamailio:snbF93@localhost/kamailio")
# in 3.3 the fallback2db change to subs_db_mode
modparam("presence", "subs_db_mode", 3)
modparam("presence", "notifier_processes", 3)


loadmodule "presence_xml.so"
modparam("presence_xml", "db_url",
"mysql://kamailio:snbF93@localhost/kamailio")
modparam("presence_xml", "force_active", 0)
modparam("presence_xml", "integrated_xcap_server", 1)
# retry-after 5 minutes
modparam("presence_xml", "xcapauth_userdel_reason",
"probation;retry-after=300")

Q: it is a bug of a feature? :)
Thanks.
Andrew