Enforce "max_wal_size/ min_wal_size must be at least twice wal_segment_size" limit while setting GUCs

Hi,

Currently postgres allows setting any value for max_wal_size or
min_wal_size, not enforcing "at least twice as wal_segment_size" limit
[1]. This isn't a problem if the server continues to run, however, the
server can't come up after a crash or restart or maintenance or
upgrade (goes to a continuous restart loop with FATAL errors [1]).

How about we add GUC check hooks for both max_wal_size and
min_wal_size where we can either emit ERROR or WARNING if values are
not "at least twice as wal_segment_size"?

Thoughts?

[1]
FATAL: "max_wal_size" must be at least twice "wal_segment_size"
FATAL: "min_wal_size" must be at least twice "wal_segment_size"

[2]
./initdb -D data
./pg_ctl -D data -l logfile start
./psql -c "alter system set max_wal_size='2MB'" postgres
./psql -c "alter system set min_wal_size='2MB'" postgres
./psql -c "select pg_reload_conf()" postgres
./pg_ctl -D data -l logfile restart

Regards,
Bharath Rupireddy.