mysql 从库I/O及SQL thread 状态解释
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8.14.6 Replication Slave I/O Thread States
The following list shows the most common states you see in the State
column for a slave server I/O thread. This state also appears in the Slave_IO_State
column displayed by SHOW SLAVE STATUS
, so you can get a good view of what is happening by using that statement.
Waiting for master update
The initial state before
Connecting to master
.Connecting to master
The thread is attempting to connect to the master.
Checking master version
A state that occurs very briefly, after the connection to the master is established.
Registering slave on master
A state that occurs very briefly after the connection to the master is established.
Requesting binlog dump
A state that occurs very briefly, after the connection to the master is established. The thread sends to the master a request for the contents of its binary logs, starting from the requested binary log file name and position.
Waiting to reconnect after a failed binlog dump request
If the binary log dump request failed (due to disconnection), the thread goes into this state while it sleeps, then tries to reconnect periodically. The interval between retries can be specified using the
CHANGE MASTER TO
statement.Reconnecting after a failed binlog dump request
The thread is trying to reconnect to the master.
Waiting for master to send event
The thread has connected to the master and is waiting for binary log events to arrive. This can last for a long time if the master is idle. If the wait lasts for
slave_net_timeout
seconds, a timeout occurs. At that point, the thread considers the connection to be broken and makes an attempt to reconnect.Queueing master event to the relay log
The thread has read an event and is copying it to the relay log so that the SQL thread can process it.
Waiting to reconnect after a failed master event read
An error occurred while reading (due to disconnection). The thread is sleeping for the number of seconds set by the
CHANGE MASTER TO
statement (default 60) before attempting to reconnect.Reconnecting after a failed master event read
The thread is trying to reconnect to the master. When connection is established again, the state becomes
Waiting for master to send event
.Waiting for the slave SQL thread to free enough relay log space
You are using a nonzero
relay_log_space_limit
value, and the relay logs have grown large enough that their combined size exceeds this value. The I/O thread is waiting until the SQL thread frees enough space by processing relay log contents so that it can delete some relay log files.Waiting for slave mutex on exit
A state that occurs briefly as the thread is stopping.
8.14.7 Replication Slave SQL Thread States
The following list shows the most common states you may see in the State
column for a slave server SQL thread:
Waiting for the next event in relay log
The initial state before
Reading event from the relay log
.Reading event from the relay log
The thread has read an event from the relay log so that the event can be processed.
Making temporary file (append) before replaying LOAD DATA INFILE
The thread is executing a
LOAD DATA INFILE
statement and is appending the data to a temporary file containing the data from which the slave will read rows.Making temporary file (create) before replaying LOAD DATA INFILE
The thread is executing a
LOAD DATA INFILE
statement and is creating a temporary file containing the data from which the slave will read rows. This state can only be encountered if the originalLOAD DATA INFILE
statement was logged by a master running a version of MySQL earlier than version 5.0.3.Slave has read all relay log; waiting for more updates
The thread has processed all events in the relay log files, and is now waiting for the I/O thread to write new events to the relay log.
Waiting for slave mutex on exit
A very brief state that occurs as the thread is stopping.
Waiting until MASTER_DELAY seconds after master executed event
The SQL thread has read an event but is waiting for the slave delay to lapse. This delay is set with the
MASTER_DELAY
option ofCHANGE MASTER TO
.Killing slave
The thread is processing a
STOP SLAVE
statement.Waiting for an event from Coordinator
Using the multi-threaded slave (
slave_parallel_workers
is greater than 1), one of the slave worker threads is waiting for an event from the coordinator thread.
The Info
column for the SQL thread may also show the text of a statement. This indicates that the thread has read an event from the relay log, extracted the statement from it, and may be executing it.
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