How to fix CR_SERVER_LOST (2013): Lost connection to MySQL server during query in MySQL

Join the error log, general query log, and status variables to understand why the server ended the session:

SHOW VARIABLES LIKE 'log_error_verbosity';
SHOW STATUS LIKE 'Aborted_%';
SHOW GLOBAL STATUS LIKE 'Connection_errors_%';

Outside the shell, run mysqladmin version to see uptime and mysqladmin variables | grep wait_timeout to check timeouts. Look for "Aborted connection" entries that mention the user/host and query ID. If you cannot reproduce the drop, briefly enable the general query log to capture the failing SQL.

Long-running queries or sleepy clients should not sit longer than the server's wait_timeout/interactive_timeout/connect_timeout. For example:

SET GLOBAL wait_timeout = 86400;
SET GLOBAL interactive_timeout = 86400;
SET GLOBAL connect_timeout = 20;

Reload your connection pool so it opens new connections more frequently than the lowest timeout, and enable connection testing (e.g., SELECT 1) before handing the socket to the application. Avoid letting pooled connections sit idle past the server's limit.

If the server kills the connection while you stream large rows or BLOBs, bump the relevant limits:

SHOW VARIABLES LIKE 'max_allowed_packet';
SET GLOBAL max_allowed_packet = 67108864;
SET GLOBAL net_write_timeout = 120;
SET GLOBAL net_read_timeout = 120;

Mirror the client-side settings in your connector (under [mysql] or connection attributes) so both sides allow the same packet size.

Oversized INSERT/UPDATE/LOAD DATA statements may be aborted because the query packet grows too large or the server abandons the connection. Split bulk work into smaller batches and commit between them:

INSERT INTO big_table (cols) VALUES (...), (...);
-- keep each batch to a few thousand rows or less than 64MB payload
COMMIT;

Use streaming APIs (e.g., mysql.connector.cursor.execute with executemany) so the client sends manageable packets.

Firewalls, routers, or cloud load balancers sometimes drop idle connections faster than mysqld or the connector. Coordinate timeouts across all layers:

- Lower proxy idle timeout to match or exceed MySQL timeouts, or add keepalive probes.
- Verify security groups/iptables allow traffic to the MySQL port throughout long-running exchanges.
- Check for duplex/MTU issues by copying a large file over the same network path.

If you run in containers, ensure Kubernetes services or sidecars do not restart pods while a query is running.

Before running heavy queries, ping the connection and reconnect if necessary. Wrap statements in retry logic that distinguishes between transient CR_SERVER_LOST errors and hard failures:

// pseudo-code
try {
  connection.ping({ reconnect: true });
  result = await connection.query(sql);
} catch (err) {
  if (isTransient(err, 2013)) {
    await delay(backoff(attempt));
    continue;
  }
  throw err;
}

Combine retries with idempotency (use unique request IDs) to avoid duplicate commits.