Editing Troubleshooting of MySQL errors (section)

=== Resolving "Host 'xx.xx.xxx.xxx' is blocked because of many connection errors" ===

Error Message

<pre>
Host 'xx.xx.xxx.xxx' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'
</pre>

Understanding the Issue

(1) Check the threshold value

MySQL's mechanism works as follows: once the same source host (identified by IP or hostname) accumulates a number of "connection errors" reaching the value configured in `max_connect_errors`, MySQL automatically blocks that source and refuses further connections from it.

<pre>
SHOW VARIABLES LIKE 'max_connect_errors';
</pre>

The threshold found was 100.

(2) Check which hosts are currently recorded/blocked

<pre>
SELECT IP, HOST, SUM_CONNECT_ERRORS, COUNT_HOST_BLOCKED_ERRORS
FROM performance_schema.host_cache
ORDER BY SUM_CONNECT_ERRORS DESC;
</pre>

Confirmed that the only blocked IP is `xx.xx.xxx.xxx`, with `SUM_CONNECT_ERRORS` exactly matching the threshold of 100, and no other IPs were affected.


Resolving the Issue

⚠️ Note: `flush-hosts` / `FLUSH HOSTS` clears the **entire** host cache, not just a single IP. If the query results show records for other hosts as well, they will all be reset at the same time. For a shared production environment, it's recommended to confirm with other administrators before running this.

(1) In a terminal or command prompt, run:

<pre>
mysqladmin -u root -p flush-hosts
</pre>

or

<pre>
mysql -u root -p
Once inside the MySQL shell, run: FLUSH HOSTS;
</pre>

Note: The `FLUSH HOSTS` syntax has been deprecated since MySQL 8.0.23 and removed in 8.4<ref>[https://dev.mysql.com/doc/refman/8.4/en/performance-schema-host-cache-table.html MySQL :: MySQL 8.4 Reference Manual :: 29.12.22.3 The host_cache Table]</ref><ref>[https://oneuptime.com/blog/post/2026-03-31-mysql-fix-max-connect-errors-blocked-hosts/view How to Fix max_connect_errors and Blocked Hosts in MySQL]</ref>. If your environment is on a newer version, use the officially recommended alternative instead:
<pre>
TRUNCATE TABLE performance_schema.host_cache;
</pre>

(2) Verify after execution

<pre>
SELECT IP, HOST, SUM_CONNECT_ERRORS, COUNT_HOST_BLOCKED_ERRORS
FROM performance_schema.host_cache
ORDER BY SUM_CONNECT_ERRORS DESC;
</pre>

Result: no rows returned (0 rows), indicating the host cache has been cleared — the previous connection error counts and blocked status have been reset, and the IP should now be able to connect normally.