MySQL: 'Lost Connection to MySQL Server' Mid-Query or Mid-Idle

Two different problems wear this one error: queries dying mid-flight (packet/timeout limits) and idle pools dying (server closes them first). Which one you have changes the fix entirely.

What you'll see

Error 2013 'Lost connection to MySQL server during query'
Or: first query after idle time fails, reconnects, then works

Root causes

wait_timeout kills idle pool connections

MySQL closes idle connections after wait_timeout (default 8h, often tuned lower). Your pool doesn't know they're dead until the next query fails.

max_allowed_packet exceeded

Large INSERT or BLOB sends hit the packet limit and the server drops the connection mid-query.

Aggressive timeouts or proxy kills

A load balancer between app and DB (or interactive_timeout vs wait_timeout confusion) reaps connections early.

Fix it

Check the timeout landscape on the server

SHOW VARIABLES WHERE Variable_name IN ('wait_timeout','interactive_timeout','max_allowed_packet');

For idle deaths, set pool keepalive/max-lifetime below server timeout
```
# e.g. HikariCP: maxLifetime = min(25min, wait_timeout - 1min)
```

For big rows, raise packet limits on both ends

SET GLOBAL max_allowed_packet = 268435456;  # and the client driver's limit

Confirm no proxy idle timeout in between

# check LB/proxy idle timeout > wait_timeout, or enable TCP keepalives

Field note

The gold rule: client pool maxLifetime must be shorter than server wait_timeout. Reconnecting on failure hides the bug; sizing the pool lifetime correctly removes it.

Common questions

Why does MySQL time out instead of refusing or accepting?

The TCP connect succeeds but the handshake stalls: DNS reverse-lookup on the server (skip_name_resolve), a saturated max_connections queue, or a middlebox dropping idle streams. connect_timeout on the server and the driver's connect timeout are different knobs.

Intermittent timeouts under load only — where do I look?

Connection churn: apps opening connections per-request exhaust the backlog. Pool connections, and check Threads_connected vs max_connections plus the Aborted_connects counter trend during the failure window.

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MySQL: 'Lost Connection to MySQL Server' Mid-Query or Mid-Idle

What you'll see

Root causes

wait_timeout kills idle pool connections

max_allowed_packet exceeded

Aggressive timeouts or proxy kills

Fix it

Field note

Common questions

Related fixes

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