When does rndc reconfig flush the cache?

Why does rndc reconfig flush the cache sometimes but not on other occasions?

Usually when issuing rndc reconfig to make changes to a running BIND 9 nameserver, you expect it to retain the current working cache of learned RRsets.

However, there are a few changes that you can make to the configuration that might be incompatible with what has already been cached - and in those circumstances, named will also start with a new and empty cache following the reconfig. Here are the settings that, if changed, will result in rndc reconfig clearing cache:

• check-names
• zero-no-soa-ttl
• max-cache-size
• max-cache-ttl
• max-ncache-ttl
• dnssec-validation
• dnssec-accept-expired