1. Have a dhcpd.leases.n filename.
2. Each of these lease files has
next file dhcpd.leases.(n+1)
   at the bottom.
3. dhcp server reads these like a linked list.


Another process aggregates these:

Starts like this:

dhcpd.leases ------> dhcpd.leases.2 -----> ... -----> dhcpd.leases.n

then starts writing dhcpd.leases.tmp, aggregating all leases from
all the leases files except the most current one, then adds at the
end:

next file dhcpd.leases.n

where n is the most current one at the time the process began running.

It then renames dhcpd.leases.tmp to dhcpd.leases, and all the
intermediate files that were aggregated can be deleted.

Note that instead of ordering the suffix, can make the suffix the
time.   The pointer at the end of the file determines the next file in
the "linked list".