MySQL server has gone away

What this means

Client error 2006 is returned when the server closes the connection while the client still has it open. This is typically caused by the connection being idle longer than wait_timeout, a query result larger than max_allowed_packet, or the server being restarted.

Why it happens

1. 1Connection was idle longer than wait_timeout (default 8 hours) and the server dropped it
2. 2Query or result set exceeds max_allowed_packet — server closes connection on oversized packet
3. 3Server was restarted while the connection was open
4. 4Network interruption between client and server
5. 5Application is reusing a connection from a pool that was silently closed by the server

How to reproduce

Executing a query on a connection that the server has already closed.

-- After a long idle period:
SELECT * FROM large_table;

Fix 1: Increase wait_timeout and interactive_timeout

When connections are legitimately idle for extended periods.

SET GLOBAL wait_timeout = 28800;          -- 8 hours
SET GLOBAL interactive_timeout = 28800;

-- Permanent setting in my.cnf:
-- wait_timeout = 28800

Fix 2: Enable connection pool reconnection / ping

In applications using a connection pool (most frameworks).

-- PDO example — enable persistent connections with ping:
$pdo = new PDO($dsn, $user, $pass, [
  PDO::ATTR_PERSISTENT => true,
  PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8mb4',
]);
-- Most ORMs have a reconnect option; enable it.

Fix 3: Increase max_allowed_packet for large queries

When the error occurs with large INSERT or BLOB operations.

SET GLOBAL max_allowed_packet = 67108864;  -- 64 MB

-- Permanent in my.cnf:
-- max_allowed_packet = 64M

What not to do

Sources

Confidence assessment

See also