MySQL 8.0 Reference Manual Including MySQL NDB Cluster 8.0
The following list shows the most common states you see in the
State
column for a replication I/O (receiver)
thread on a replica server. This state also appears in the
Replica_IO_State
column displayed by
SHOW
REPLICA STATUS
(or before MySQL 8.0.22,
SHOW
REPLICA STATUS
), so you can get a good view of what is
happening by using that statement.
In MySQL 8.0.26, incompatible changes were made to
instrumentation names, including the names of thread stages,
containing the terms “master”, which is changed to
“source”, “slave”, which is changed to
“replica”, and “mts” (for
“multithreaded slave”), which is changed to
“mta” (for “multithreaded applier”).
Monitoring tools that work with these instrumentation names
might be impacted. If the incompatible changes have an impact
for you, set the
terminology_use_previous
system
variable to BEFORE_8_0_26
to make MySQL
Server use the old versions of the names for the objects
specified in the previous list. This enables monitoring tools
that rely on the old names to continue working until they can be
updated to use the new names.
Set the
terminology_use_previous
system
variable with session scope to support individual functions, or
global scope to be a default for all new sessions. When global
scope is used, the slow query log contains the old versions of
the names.
From MySQL 8.0.26: Checking source
version
A state that occurs very briefly, after the connection to the source is established.
From MySQL 8.0.26: Connecting to source
The thread is attempting to connect to the source.
Queueing master event to the relay log
From MySQL 8.0.26: Queueing source 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.
Reconnecting after a failed binlog dump
request
The thread is trying to reconnect to the source.
Reconnecting after a failed master event
read
From MySQL 8.0.26: Reconnecting after a failed
source event read
The thread is trying to reconnect to the source. When
connection is established again, the state becomes
Waiting for master to send event
.
From MySQL 8.0.26: Registering replica on
source
A state that occurs very briefly after the connection to the source is established.
A state that occurs very briefly, after the connection to the source is established. The thread sends to the source a request for the contents of its binary logs, starting from the requested binary log file name and position.
Waiting for its turn to commit
A state that occurs when the replica thread is waiting for
older worker threads to commit if
replica_preserve_commit_order
or
slave_preserve_commit_order
is enabled.
Waiting for master to send event
From MySQL 8.0.26: Waiting for source to send
event
The thread has connected to the source and is waiting for
binary log events to arrive. This can last for a long time
if the source is idle. If the wait lasts for
replica_net_timeout
or
slave_net_timeout
seconds,
a timeout occurs. At that point, the thread considers the
connection to be broken and makes an attempt to reconnect.
From MySQL 8.0.26: Waiting for source
update
The initial state before Connecting to
master
or Connecting to source
.
Waiting for slave mutex on exit
From MySQL 8.0.26: Waiting for replica mutex on
exit
A state that occurs briefly as the thread is stopping.
Waiting for the slave SQL thread to free enough
relay log space
From MySQL 8.0.26: Waiting for the replica 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 (receiver) thread
is waiting until the SQL (applier) thread frees enough space
by processing relay log contents so that it can delete some
relay log files.
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 REPLICATION SOURCE TO
statement (from MySQL 8.0.23) or CHANGE
MASTER TO
statement (before MySQL 8.0.23).
Waiting to reconnect after a failed master event
read
From MySQL 8.0.26: Waiting to reconnect after a
failed source event read
An error occurred while reading (due to disconnection). The
thread is sleeping for the number of seconds set by the
CHANGE REPLICATION SOURCE TO
statement (from MySQL 8.0.23) or CHANGE
MASTER TO
statement (before MySQL 8.0.23), which
defaults to 60, before attempting to reconnect.