using version 5.2.0-rc0 of kamailio, we are trying to track the dialogs of dialog module using db_redis module with this setup
#!define DBURL_DIALOG "redis://127.0.0.1:6390/7"

# ----- dialog params -----
modparam("dialog", "db_url", DBURL_DIALOG)
modparam("dialog", "enable_stats", 1)
modparam("dialog", "hash_size", 16384)
modparam("dialog", "dlg_flag", 31)
modparam("dialog", "dlg_match_mode", 1)
modparam("dialog", "db_mode", 1)
modparam("dialog", "timer_procs", 1)
modparam("dialog", "db_update_period", 1)

# ----- db_redis params -----
modparam("db_redis", "schema_path", "/usr/local/kamailio/share/kamailio/db_redis/kamailio")
modparam("db_redis", "keys", "dialog=entry:hash_entry,hash_id,callid")
modparam("db_redis", "keys", "dialog_vars=entry:hash_entry,hash_id,dialog_key,dialog_value")

and we see it works and if a kamailio instance resets in the middle of a dialog it recovers all the dlg_vars and values because we have the db_skip_load to 0 in dialog module.

But we have noticed that the redis is being written with the information of the dlg_var assigned until that moment when we get a provisional response with SDP, and we dom see a set on the redis with the dialog entry and id untill call is connected.

Nov 16 13:22:55 proxy-1 /usr/local/kamailio/sbin/kamailio[22424]: INFO: Call-ID 1-1511@9.7.8.1: Status 180
Nov 16 13:22:55 proxy-1 /usr/local/kamailio/sbin/kamailio[22424]: WARNING: db_redis [redis_dbase.c:1489]: db_redis_perform_update(): performing full table scan on table 'dialog' while performing update
Nov 16 13:22:55 proxy-1 /usr/local/kamailio/sbin/kamailio[22424]: WARNING: db_redis [redis_dbase.c:1492]: db_redis_perform_update():   scan key 0 is 'hash_entry'
Nov 16 13:22:55 proxy-1 /usr/local/kamailio/sbin/kamailio[22424]: WARNING: db_redis [redis_dbase.c:1492]: db_redis_perform_update():   scan key 1 is 'hash_id'

on the redis (we only see hmset for dialog_vars key)
1542374575.721816 [7 127.0.0.1:56858] "HMSET" "dialog_vars:entry::13725:16494:_uac_funew:sip:1231215423@voda.interconnect.manxtelecom.im" "hash_entry" "13725" "hash_id" "16494" "dialog_key" "_uac_funew" "dialog_value" "sip:1231215423@voda.interconnect.manxtelecom.im"
1542374575.722001 [7 127.0.0.1:56858] "HMSET" "dialog_vars:entry::13725:16494:_uac_fu:sip:anonymous@voda.interconnect.manxtelecom.im" "hash_entry" "13725" "hash_id" "16494" "dialog_key" "_uac_fu" "dialog_value" "sip:anonymous@voda.interconnect.manxtelecom.im"
....