Performance Schema Miscellaneous Tables as well as the size of the  host_cache  table. For operational and configuration information about the host cache, see Section 5.1.12.3, “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  host_cache  table has these columns: The IP address of the client that connected to the server, expressed as a string. The resolved DNS host name for that client IP, or  NULL  if the name is unknown. Whether the IP-to-host name-to-IP DNS resolution was performed successfully for the client IP. If HOST_VALIDATED  is  YES , the  HOST  column is used as the host name corresponding to the IP so that additional calls to DNS can be avoided. While  HOST_VALIDATED  is  NO , DNS resolution is attempted for each connection attempt, until it eventually completes with either a valid result or a permanent error. This information enables the server to avoid caching bad or missing host names during temporary DNS failures, which would negatively affect clients forever. The number of connection errors that are deemed “blocking”  (assessed against the max_connect_errors  system variable). Only protocol handshake errors are counted, and only for hosts that passed validation ( HOST_VALIDATED = YES ). Once  SUM_CONNECT_ERRORS  for a given host reaches the value of  max_connect_errors , new connections from that host are blocked. The  SUM_CONNECT_ERRORS  value can exceed the  max_connect_errors  value because multiple connection attempts from a host can occur simultaneously while the host is not blocked. Any or all of them can fail, independently incrementing SUM_CONNECT_ERRORS , possibly beyond the value of  max_connect_errors . Suppose that  max_connect_errors  is 200 and  SUM_CONNECT_ERRORS  for a given host is 199. If 10 clients attempt to connect from that host simultaneously, none of them are blocked because  SUM_CONNECT_ERRORS  has not reached 200. If blocking errors occur for five of the clients, SUM_CONNECT_ERRORS  is increased by one for each client, for a resulting  SUM_CONNECT_ERRORS value of 204. The other five clients succeed and are not blocked because the value of SUM_CONNECT_ERRORS  when their connection attempts began had not reached 200. New connections from the host that begin after  SUM_CONNECT_ERRORS  reaches 200 are blocked. The number of connections that were blocked because  SUM_CONNECT_ERRORS  exceeded the value of the  max_connect_errors  system variable. The number of transient errors during IP-to-host name DNS resolution. The number of permanent errors during IP-to-host name DNS resolution. • COUNT_NAMEINFO_PERMANENT_ERRORS • COUNT_NAMEINFO_TRANSIENT_ERRORS • COUNT_HOST_BLOCKED_ERRORS • SUM_CONNECT_ERRORS • HOST_VALIDATED • HOST • IP 5081