MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6

24.12.16.1 The host_cache Table

The MySQL server maintains an in-memory host cache that contains client host name and IP address information and is used to avoid Domain Name System (DNS) lookups. The host_cache table exposes the contents of this cache. The host_cache_size system variable controls the size of the host cache, as well as the size of the host_cache table. For operational and configuration information about the host cache, see Section 5.1.11.2, “DNS Lookups and the Host Cache”.

Because the host_cache table exposes the contents of the host cache, it can be examined using SELECT statements. This may help you diagnose the causes of connection problems. The Performance Schema must be enabled or this table is empty.

The host_cache table has these columns:

TRUNCATE TABLE is permitted for the host_cache table. It requires the DROP privilege for the table. Truncating the table flushes the host cache, which has the effects described in Flushing the Host Cache.