[SR-Users] dispatcher algorithm 11, no more than 25 hosts in group for proper distribution

[Ivan Matvieiev]

Hello Community,

There is a module dispatcher and sharing algorithm 11 that features
the ability to redistribute load when the host is enabled or disabled
that is quite valuable for me.
In the test lab I faced unexpected behavior:
- when I add to group <=25 hosts algorithm behaves as per description.
- when a group includes 26 or more hosts, and 100 calls are done for
instance, then about 25 go to the first host and 75 are distributed
among the rest of hosts.

Expected behavior: all hosts of the group having the same rweight
value must receive the same amount of calls no mater what number of
hosts is in the group.

Could you please to help to figure out what is wrong and why when the
dispatcher group consists of 26+ hosts dispatching algorithm 11
behaves differently than when group consists of 25 or less of hosts?

Some configuration notes:
# module configs
modparam("dispatcher", "list_file", "/etc/kamailio/dispatcher.list")
modparam("dispatcher", "flags", 2)
modparam("dispatcher", "ds_ping_method", "OPTIONS")
modparam("dispatcher", "ds_probing_threshold", 3)
modparam("dispatcher", "ds_inactive_threshold", 10)
modparam("dispatcher", "ds_probing_mode", 3)
modparam("dispatcher", "ds_ping_interval", 10)
modparam("dispatcher", "ds_ping_reply_codes", "501,403,404,400,200")
modparam("dispatcher", "ds_ping_from",DS_PING_FROM_PARAM)
modparam("dispatcher", "use_default", 0)

# dispatching algorithm call
if ( ds_is_from_list("101")) {
     sl_send_reply("100","My calls");
     ds_select_dst("100", "11");
     return;
}

# dispatcher list group config
100 sip:10.60.27.123:7000 0 10 rweight=50
100 sip:10.60.27.123:7001 0 10 rweight=50
100 sip:10.60.27.123:7002 0 10 rweight=50
100 sip:10.60.27.123:7003 0 10 rweight=50
100 sip:10.60.27.123:7004 0 10 rweight=50
100 sip:10.60.27.123:7005 0 10 rweight=50
100 sip:10.60.27.123:7006 0 10 rweight=50
100 sip:10.60.27.123:7007 0 10 rweight=50
100 sip:10.60.27.123:7008 0 10 rweight=50
100 sip:10.60.27.123:7009 0 10 rweight=50
100 sip:10.60.27.123:7010 0 10 rweight=50
100 sip:10.60.27.123:7011 0 10 rweight=50
100 sip:10.60.27.123:7012 0 10 rweight=50
100 sip:10.60.27.123:7013 0 10 rweight=50
100 sip:10.60.27.123:7014 0 10 rweight=50
100 sip:10.60.27.123:7015 0 10 rweight=50
100 sip:10.60.27.123:7016 0 10 rweight=50
100 sip:10.60.27.123:7017 0 10 rweight=50
100 sip:10.60.27.123:7018 0 10 rweight=50
100 sip:10.60.27.123:7019 0 10 rweight=50
100 sip:10.60.27.123:7020 0 10 rweight=50
100 sip:10.60.27.123:7021 0 10 rweight=50
100 sip:10.60.27.123:7022 0 10 rweight=50
100 sip:10.60.27.123:7023 0 10 rweight=50
100 sip:10.60.27.123:7024 0 10 rweight=50

Kamailio version:
kamailio -v
version: kamailio 5.4.4 (x86_64/linux) e16352
flags: USE_TCP, USE_TLS, USE_SCTP, TLS_HOOKS, USE_RAW_SOCKS,
DISABLE_NAGLE, USE_MCAST, DNS_IP_HACK, SHM_MMAP, PKG_MALLOC, Q_MALLOC,
F_MALLOC, TLSF_MALLOC, DBG_SR_MEMORY, USE_FUTEX,
FAST_LOCK-ADAPTIVE_WAIT, USE_DNS_CACHE, USE_DNS_FAILOVER, USE_NAPTR,
USE_DST_BLACKLIST, HAVE_RESOLV_RES
ADAPTIVE_WAIT_LOOPS 1024, MAX_RECV_BUFFER_SIZE 262144, MAX_URI_SIZE
1024, BUF_SIZE 65535, DEFAULT PKG_SIZE 8MB
poll method support: poll, epoll_lt, epoll_et, sigio_rt, select.
id: e16352
compiled on 15:56:46 Feb 15 2021 with gcc 4.8.5

System info
CentOS Linux release 7.7.1908 (Core)
Linux test-carrier-1.loc 3.10.0-1062.4.1.el7.x86_64 #1 SMP Fri Oct 18
17:15:30 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux