Rechercher dans le manuel MySQL
17.4.1.20 Replication and max_allowed_packet
max_allowed_packet
sets an
upper limit on the size of any single message between the MySQL
server and clients, including replication slaves. If you are
replicating large column values (such as might be found in
TEXT
or
BLOB
columns) and
max_allowed_packet
is too small
on the master, the master fails with an error, and the slave
shuts down the I/O thread. If
max_allowed_packet
is too small
on the slave, this also causes the slave to stop the I/O thread.
Row-based replication currently sends all columns and column
values for updated rows from the master to the slave, including
values of columns that were not actually changed by the update.
This means that, when you are replicating large column values
using row-based replication, you must take care to set
max_allowed_packet
large enough
to accommodate the largest row in any table to be replicated,
even if you are replicating updates only, or you are inserting
only relatively small values.
On a multi-threaded slave (with
slave_parallel_workers > 0
),
ensure that the
slave_pending_jobs_size_max
system variable is set to a value equal to or greater than the
setting for the
max_allowed_packet
system
variable on the master. The default setting for
slave_pending_jobs_size_max
,
128M, is twice the default setting for
max_allowed_packet
, which is
64M. max_allowed_packet
limits
the packet size that the master will send, but the addition of
an event header can produce a binary log event exceeding this
size. Also, in row-based replication, a single event can be
significantly larger than the
max_allowed_packet
size,
because the value of
max_allowed_packet
only limits
each column of the table.
The replication slave actually accepts packets up to the limit
set by its
slave_max_allowed_packet
setting, which defaults to the maximum setting of 1GB, to
prevent a replication failure due to a large packet. However,
the value of
slave_pending_jobs_size_max
controls the memory that is made available on the slave to hold
incoming packets. The specified memory is shared among all the
slave worker queues.
The value of
slave_pending_jobs_size_max
is
a soft limit, and if an unusually large event (consisting of one
or multiple packets) exceeds this size, the transaction is held
until all the slave workers have empty queues, and then
processed. All subsequent transactions are held until the large
transaction has been completed. So although unusual events
larger than
slave_pending_jobs_size_max
can
be processed, the delay to clear the queues of all the slave
workers and the wait to queue subsequent transactions can cause
lag on the replication slave and decreased concurrency of the
slave workers.
slave_pending_jobs_size_max
should therefore be set high enough to accommodate most expected
event sizes.
Document created the 26/06/2006, last modified the 26/10/2018
Source of the printed document:https://www.gaudry.be/en/mysql-rf-replication-features-max-allowed-packet.html
The infobrol is a personal site whose content is my sole responsibility. The text is available under CreativeCommons license (BY-NC-SA). More info on the terms of use and the author.
References
These references and links indicate documents consulted during the writing of this page, or which may provide additional information, but the authors of these sources can not be held responsible for the content of this page.
The author This site is solely responsible for the way in which the various concepts, and the freedoms that are taken with the reference works, are presented here. Remember that you must cross multiple source information to reduce the risk of errors.