A communication packet is a single SQL statement sent to the MySQL server, a single row that is sent to the client, or a binary log event sent from a master replication server to a slave.
The largest possible packet that can be transmitted to or from a MySQL 5.1 server or client is 1GB.
When a MySQL client or the mysqld server
receives a packet bigger than
max_allowed_packet bytes, it
and closes the connection. With some clients, you may also get
Lost connection to MySQL server during
query error if the communication packet is too
Both the client and the server have their own
so if you want to handle big packets, you must increase this
variable both in the client and in the server.
That sets the packet size to 32MB.
The server's default
max_allowed_packet value is
1MB. You can increase this if the server needs to handle big
queries (for example, if you are working with big
BLOB columns). For example, to
set the variable to 16MB, start the server like this:
You can also use an option file to set
example, to set the size for the server to 16MB, add the
following lines in an option file:
It is safe to increase the value of this variable because the extra memory is allocated only when needed. For example, mysqld allocates more memory only when you issue a long query or when mysqld must return a large result row. The small default value of the variable is a precaution to catch incorrect packets between the client and server and also to ensure that you do not run out of memory by using large packets accidentally.
You can also get strange problems with large packets if you
are using large
BLOB values but
have not given mysqld access to enough
memory to handle the query. If you suspect this is the case,
try adding ulimit -d 256000 to the
beginning of the mysqld_safe script and