Lost connection to MySQL server during query

What this means

Client error 2013 is raised when the connection to the server is lost while a query is actively executing — as opposed to error 2006 which happens on an idle connection. Common causes are net_read_timeout, net_write_timeout expiry, or a query result exceeding max_allowed_packet.

Why it happens

1. 1Query takes longer than net_read_timeout to return the first row (client-side timeout)
2. 2Result set is larger than max_allowed_packet — server drops the connection mid-transfer
3. 3Server OOM or crash during query execution
4. 4Network interruption during a long-running query
5. 5Client-side read timeout set too low in the driver or framework

How to reproduce

Executing a long-running query or fetching a large result set.

SELECT * FROM audit_log;  -- millions of rows, large BLOBs

Fix 1: Increase net_read_timeout and net_write_timeout

When long-running queries time out before completing.

SET GLOBAL net_read_timeout = 300;   -- 5 minutes
SET GLOBAL net_write_timeout = 300;

Fix 2: Increase max_allowed_packet

When fetching rows with large BLOB or TEXT columns.

SET GLOBAL max_allowed_packet = 134217728;  -- 128 MB

Fix 3: Paginate large queries instead of fetching all rows

When the full result set is too large to transfer in one go.

-- Use LIMIT + OFFSET for pagination:
SELECT * FROM audit_log ORDER BY id LIMIT 1000 OFFSET 0;
SELECT * FROM audit_log ORDER BY id LIMIT 1000 OFFSET 1000;
-- Or cursor-based pagination with a WHERE id > last_seen_id

What not to do

Sources

Confidence assessment

See also