I don't know if this has been changed in 9.1 but in 9.0.5 we were
trying to set up streaming replication and kept getting the warning
about wal_level=minimal and hence hot standby not being possible. It
was the same message as this (found in one of the emails I found when
researching the problem):
WARNING: WAL was generated with wal_level=minimal, data may be missing
HINT: This happens if you temporarily set wal_level=minimal without
taking a new base backup.
FATAL: hot standby is not possible because wal_level was not set to
"hot_standby" on the master server
After a bunch of troubleshooting I discovered the problem:
primary_conninfo was not set in the recovery.conf. Apparently this
error will be thrown not only due to wal levels being inadequate but
due to not being told to connect to the primary.
I know this won't get changed in a stable branch, but it might save a
bunch of people significant stress if this condition had its own error
message, if this hasn't been done already for 9.1.
Best Wishes,
Chris Travers