MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6
START SLAVE [thread_types
] [until_option
] [connection_options
] [channel_option
]thread_types
: [thread_type
[,thread_type
] ... ]thread_type
: IO_THREAD | SQL_THREADuntil_option
: UNTIL { {SQL_BEFORE_GTIDS | SQL_AFTER_GTIDS} =gtid_set
| MASTER_LOG_FILE = 'log_name
', MASTER_LOG_POS =log_pos
| RELAY_LOG_FILE = 'log_name
', RELAY_LOG_POS =log_pos
| SQL_AFTER_MTS_GAPS }connection_options
: [USER='user_name
'] [PASSWORD='user_pass
'] [DEFAULT_AUTH='plugin_name
'] [PLUGIN_DIR='plugin_dir
']channel_option
: FOR CHANNELchannel
gtid_set
:uuid_set
[,uuid_set
] ... | ''uuid_set
:uuid
:interval
[:interval
]...uuid
:hhhhhhhh
-hhhh
-hhhh
-hhhh
-hhhhhhhhhhhh
h
: [0-9,A-F]interval
:n
[-n
] (n
>= 1)
START SLAVE
with no
thread_type
options starts both of
the replication threads. The replication I/O thread reads events
from the source server and stores them in the relay log. The
replication SQL thread reads events from the relay log and
executes them. START SLAVE
requires the SUPER
privilege.
If START SLAVE
succeeds in
starting the replication threads, it returns without any error.
However, even in that case, it might be that the replication
threads start and then later stop (for example, because they do
not manage to connect to the source or read its binary log, or
some other problem). START SLAVE
does not warn you about this. You must check the replica's error
log for error messages generated by the replication threads, or
check that they are running satisfactorily with
SHOW SLAVE STATUS
.
START SLAVE
causes an implicit commit of an
ongoing transaction. See Section 13.3.3, “Statements That Cause an Implicit Commit”.
gtid_next
must be set to
AUTOMATIC
before issuing this statement.
The optional FOR CHANNEL
clause enables you
to name which replication channel the statement applies to.
Providing a channel
FOR CHANNEL
clause applies the
channel
START SLAVE
statement to a specific
replication channel. If no clause is named and no extra channels
exist, the statement applies to the default channel. If a
START SLAVE
statement does not have a channel
defined when using multiple channels, this statement starts the
specified threads for all channels. This statement is disallowed
for the group_replication_recovery
channel.
See Section 16.2.2, “Replication Channels” for more information.
You can add IO_THREAD
and
SQL_THREAD
options to the statement to name
which of the threads to start. Note that the Group Replication
applier channel (group_replication_applier
)
has no I/O thread, only an SQL thread. Specifying the
IO_THREAD
or SQL_THREAD
options when you start this channel has no benefit.
START SLAVE
supports pluggable user-password
authentication with the USER
,
PASSWORD
, DEFAULT_AUTH
and
PLUGIN_DIR
options, as described in the
following list:
USER
: User name. Cannot be set to an
empty or null string, or left unset if
PASSWORD
is used.
PASSWORD
: Password.
DEFAULT_AUTH
: Name of plugin; default is
MySQL native authentication.
PLUGIN_DIR
: Location of plugin.
You cannot use the SQL_THREAD
option when
specifying any of USER
,
PASSWORD
, DEFAULT_AUTH
, or
PLUGIN_DIR
, unless the
IO_THREAD
option is also provided.
For more information, see Section 6.2.13, “Pluggable Authentication”.
If an insecure connection is used with any these options, the server issues the warning Sending passwords in plain text without SSL/TLS is extremely insecure.
START SLAVE ... UNTIL
supports two additional
options for use with global transaction identifiers (GTIDs) (see
Section 16.1.3, “Replication with Global Transaction Identifiers”). Each of these takes a set
of one or more global transaction identifiers
gtid_set
as an argument (see
GTID Sets, for more
information).
When no thread_type
is specified,
START SLAVE UNTIL SQL_BEFORE_GTIDS
causes the
replication SQL thread to process transactions until it has
reached the first transaction whose GTID is
listed in the gtid_set
.
START SLAVE UNTIL SQL_AFTER_GTIDS
causes the
replication threads to process all transactions until the
last
transaction in the
gtid_set
has been processed by both
threads. In other words, START SLAVE UNTIL
SQL_BEFORE_GTIDS
causes the replication SQL thread to
process all transactions occurring before the first GTID in the
gtid_set
is reached, and
START SLAVE UNTIL SQL_AFTER_GTIDS
causes the
replication threads to handle all transactions, including those
whose GTIDs are found in gtid_set
,
until each has encountered a transaction whose GTID is not part
of the set. SQL_BEFORE_GTIDS
and
SQL_AFTER_GTIDS
each support the
SQL_THREAD
and IO_THREAD
options, although using IO_THREAD
with them
currently has no effect.
For example, START SLAVE SQL_THREAD UNTIL
SQL_BEFORE_GTIDS =
3E11FA47-71CA-11E1-9E33-C80AA9429562:11-56
causes the
replication SQL thread to process all transactions originating
from the source whose
server_uuid
is
3E11FA47-71CA-11E1-9E33-C80AA9429562
until it
encounters the transaction having sequence number 11; it then
stops without processing this transaction. In other words, all
transactions up to and including the transaction with sequence
number 10 are processed. Executing START SLAVE
SQL_THREAD UNTIL SQL_AFTER_GTIDS =
3E11FA47-71CA-11E1-9E33-C80AA9429562:11-56
, on the
other hand, would cause the replication SQL thread to obtain all
transactions just mentioned from the source, including all of
the transactions having the sequence numbers 11 through 56, and
then to stop without processing any additional transactions;
that is, the transaction having sequence number 56 would be the
last transaction fetched by the replication SQL thread.
When using a multithreaded replica, there is a chance of gaps in the sequence of transactions that have been executed from the relay log in the following cases:
killing the coordinator thread
after an error occurs in the worker threads
mysqld shuts down unexpectedly
Use the START SLAVE
UNTIL SQL_AFTER_MTS_GAPS
statement to cause a
multithreaded replica's worker threads to only run until no
more gaps are found in the relay log, and then to stop. This
statement can take an SQL_THREAD
option, but
the effects of the statement remain unchanged. It has no effect
on the replication I/O thread (and cannot be used with the
IO_THREAD
option).
Issuing START SLAVE
on a
multithreaded replica with gaps in the sequence of transactions
executed from the relay log generates a warning. In such a
situation, the solution is to use
START SLAVE UNTIL
SQL_AFTER_MTS_GAPS
, then issue
RESET SLAVE
to remove any
remaining relay logs. See
Section 16.4.1.32, “Replication and Transaction Inconsistencies”
for more information.
To change a failed multithreaded replica to single-threaded mode, you can issue the following series of statements, in the order shown:
START SLAVE UNTIL SQL_AFTER_MTS_GAPS; SET @@GLOBAL.slave_parallel_workers = 0; START SLAVE SQL_THREAD;
It is possible to view the entire text of a running
START SLAVE ...
statement, including any
USER
or PASSWORD
values
used, in the output of SHOW
PROCESSLIST
. This is also true for the text of a
running CHANGE MASTER TO
statement, including any values it employs for
MASTER_USER
or
MASTER_PASSWORD
.
START SLAVE
sends an
acknowledgment to the user after both the replication I/O thread
and the replication SQL thread have started. However, the
replication I/O thread may not yet have connected. For this
reason, a successful START SLAVE
causes SHOW SLAVE STATUS
to show
Slave_SQL_Running=Yes
, but this does not
guarantee that Slave_IO_Running=Yes
(because
Slave_IO_Running=Yes
only if the replication
I/O thread is running and connected). For
more information, see Section 13.7.5.34, “SHOW SLAVE STATUS Statement”, and
Section 16.1.7.1, “Checking Replication Status”.
An UNTIL
clause
(until_option
, in the preceding
grammar) may be added to specify that the replica should start
and run until the replication SQL thread reaches a given point
in the source's binary log, specified by the
MASTER_LOG_POS
and MASTER_LOG_FILE options,
or a given point in the replica's relay log, indicated with the
RELAY_LOG_POS
and
RELAY_LOG_FILE
options. When the SQL thread
reaches the point specified, it stops. If the
SQL_THREAD
option is specified in the
statement, it starts only the SQL thread. Otherwise, it starts
both replication threads. If the SQL thread is running, the
UNTIL
clause is ignored and a warning is
issued. You cannot use an UNTIL
clause with
the IO_THREAD
option.
It is also possible with START SLAVE UNTIL
to
specify a stop point relative to a given GTID or set of GTIDs
using one of the options SQL_BEFORE_GTIDS
or
SQL_AFTER_GTIDS
, as explained previously in
this section. When using one of these options, you can specify
SQL_THREAD
, IO_THREAD
,
both of these, or neither of them. If you specify only
SQL_THREAD
, then only the replication SQL
thread is affected by the statement; if only
IO_THREAD
is used, then only the replication
I/O thread is affected. If both SQL_THREAD
and IO_THREAD
are used, or if neither of them
is used, then both the replication threads are affected by the
statement.
For an UNTIL
clause, you must specify any one
of the following:
Both a log file name and a position in that file
Either of
SQL_BEFORE_GTIDS
or
SQL_AFTER_GTIDS
SQL_AFTER_MTS_GAPS
Do not mix source and relay log options. Do not mix log file options with GTID options.
The UNTIL
clause is not supported for
multithreaded replicas except when also using
SQL_AFTER_MTS_GAPS
.
If UNTIL
is used on a multithreaded replica
without
SQL_AFTER_MTS_GAPS
,
the replica operates in single-threaded (sequential) mode for
replication until the point specified by the
UNTIL
clause is reached.
Any UNTIL
condition is reset by a subsequent
STOP SLAVE
statement, a
START SLAVE
statement that
includes no UNTIL
clause, or a server
restart.
When specifying a log file and position, you can use the
IO_THREAD
option with START SLAVE
... UNTIL
even though only the replication SQL thread
is affected by this statement. The IO_THREAD
option is ignored in such cases. The preceding restriction does
not apply when using one of the GTID options
(SQL_BEFORE_GTIDS
and
SQL_AFTER_GTIDS
); the GTID options support
both SQL_THREAD
and
IO_THREAD
, as explained previously in this
section.
The UNTIL
clause can be useful for debugging
replication, or to cause replication to proceed until just
before the point where you want to avoid having the replica
replicate an event. For example, if an unwise
DROP TABLE
statement was executed
on the source, you can use UNTIL
to tell the
replica to execute up to that point but no farther. To find what
the event is, use mysqlbinlog with the
source's binary log or the replica's relay log, or by using a
SHOW BINLOG EVENTS
statement.
If you are using UNTIL
to have the replica
process replicated queries in sections, it is recommended that
you start the replica with the
--skip-slave-start
option to
prevent the SQL thread from running when the replica server
starts. It is probably best to use this option in an option file
rather than on the command line, so that an unexpected server
restart does not cause it to be forgotten.
The SHOW SLAVE STATUS
statement
includes output fields that display the current values of the
UNTIL
condition.