dhcp fails with big dhcpd.leases

[dorian]

Hello everybody,
I have a problem with dhcp server working in hotspot (public place).
It stops working when the dhcpd.leases grows to much.
I observed that having dhcp.lease file size around 893116 bytes causes
clients not to get the IP address.
To be precise: sometimes (but very seldom) it services the requests. But
generally does not.

In that case the log content is like this:
Aug 31 15:34:26 [dhcpd] DHCPDISCOVER from 00:23:6c:73:b3:29 (AMs-iPhone)
via br0
Aug 31 15:34:26 [dhcpd] DHCPOFFER on 172.16.221.214 to 00:23:6c:73:b3:29
(AMs-iPhone) via br0
Aug 31 15:34:33 [dhcpd] DHCPDISCOVER from 00:19:d2:97:ca:81 (N0336) via br0
Aug 31 15:34:33 [dhcpd] DHCPOFFER on 172.16.215.48 to 00:19:d2:97:ca:81
(N0336) via br0
Aug 31 15:34:34 [dhcpd] DHCPREQUEST for 192.168.1.101 from
00:23:6c:2b:08:eb via br0: wrong network.
Aug 31 15:34:34 [dhcpd] DHCPNAK on 192.168.1.101 to 00:23:6c:2b:08:eb
via br0
Aug 31 15:34:34 [dhcpd] DHCPDISCOVER from 00:23:6c:73:b3:29 (AMs-iPhone)
via br0
Aug 31 15:34:34 [dhcpd] DHCPOFFER on 172.16.221.214 to 00:23:6c:73:b3:29
(AMs-iPhone) via br0

After stopping the server, removing dhcpd.leases and next running it again
the log content is like the following:
Aug 31 15:34:42 [dhcpd] DHCPREQUEST for 172.19.235.111 (172.16.0.1) from
00:23:6c:2b:08:eb (kPhone) via br0
Aug 31 15:34:42 [dhcpd] DHCPACK on 172.19.235.111 to 00:23:6c:2b:08:eb
(kPhone) via br0
Aug 31 15:34:43 [dhcpd] DHCPDISCOVER from 00:23:6c:73:b3:29 via br0
Aug 31 15:34:44 [dhcpd] DHCPOFFER on 172.18.100.204 to 00:23:6c:73:b3:29
(AMs-iPhone) via br0
Aug 31 15:34:44 [dhcpd] DHCPDISCOVER from 00:25:bc:bb:d5:ac via br0
Aug 31 15:34:45 [dhcpd] DHCPOFFER on 172.16.222.41 to 00:25:bc:bb:d5:ac
(iPhone-user) via br0
Aug 31 15:34:46 [dhcpd] if AMs-iPhone.moben IN A rrset doesn't exist add
AMs-iPhone.moben 36000 IN A 172.18.100.204: timed out.
Aug 31 15:34:46 [dhcpd] DHCPREQUEST for 172.18.100.204 (172.16.0.1) from
00:23:6c:73:b3:29 (AMs-iPhone) via br0
Aug 31 15:34:46 [dhcpd] DHCPACK on 172.18.100.204 to 00:23:6c:73:b3:29
(AMs-iPhone) via br0
Aug 31 15:34:47 [dhcpd] if AMs-iPhone.moben IN A rrset doesn't exist add
AMs-iPhone.moben 36000 IN A 172.18.100.204: timed out.
Aug 31 15:34:47 [dhcpd] DHCPREQUEST for 172.18.100.204 (172.16.0.1) from
00:23:6c:73:b3:29 (AMs-iPhone) via br0
Aug 31 15:34:47 [dhcpd] DHCPACK on 172.18.100.204 to 00:23:6c:73:b3:29
(AMs-iPhone) via br0
Aug 31 15:34:49 [dhcpd] if iPhone-user.moben IN A rrset doesn't exist
add iPhone-user.moben 36000 IN A 172.16.222.41: timed out.

so it is clearly visible that in case of the failure there is no
DHCPACK  packets.

The conf file is following:

ddns-update-style ad-hoc;
log-facility local7;
#--------- 172.16.0.0/14----------------------------
subnet 172.16.0.0 netmask 255.252.0.0 {
   authoritative;
   option subnet-mask   255.252.0.0;
   option routers 172.16.0.1;
   option domain-name "moben";
   option domain-name-servers 10.2.0.1;
   option interface-mtu 1450;
   default-lease-time 72000;
   max-lease-time 72000;
   range 172.16.8.0  172.19.255.254;
}
+ some static leases based on hw address which gives addresses <172.16.8.0

The questions are:
1. why the server stop working?
2. the dhcpd.leases file size is the reason (or is it the only reason)?
3. how to fix the problem (it is 24/24 service so restarting is not the
best solution for me)

Regards,
Dorian