This section explains how to work with replication filters when multiple replication channels exist, for example in a multi-source replication topology. Before MySQL 8.0, replication filters were global, so filters were applied to all replication channels. From MySQL 8.0, replication filters can be global or channel specific, enabling you to configure multi-source replication slaves with replication filters on specific replication channels. Channel specific replication filters are particularly useful in a multi-source replication topology when the same database or table is present on multiple masters, and the slave is only required to replicate it from one master.
Each channel on a multi-source replication slave must replicate from a different master. You cannot set up multiple replication channels from a single slave to a single master, even if you use replication filters to select different data to replicate on each channel. This is because the server IDs of replication slaves must be unique in a replication topology. The master distinguishes slaves only by their server IDs, not by the names of the replication channels, so it cannot recognize different replication channels from the same slave.
On a MySQL server instance that is configured for Group
Replication, channel specific replication filters can be used
on replication channels that are not directly involved with
Group Replication, such as where a group member also acts as a
replication slave to a master that is outside the group. They
cannot be used on the
Filtering on these channels would make the group unable to
reach agreement on a consistent state.
When multiple replication channels exist, for example in a multi-source replication topology, replication filters are applied as follows:
Any global replication filter specified is added to the global replication filters of the filter type (
do_ignore_table, and so on).
Any channel specific replication filter adds the filter to the specified channel’s replication filters for the specified filter type.
Each slave replication channel copies global replication filters to its channel specific replication filters if no channel specific replication filter of this type is configured.
Each channel uses its channel specific replication filters to filter the replication stream.
The syntax to create channel specific replication filters
extends the existing SQL statements and command options. When
a replication channel is not specified the global replication
filter is configured to ensure backwards compatibility. The
CHANGE REPLICATION FILTER
statement supports the
FOR CHANNEL clause
to configure channel specific filters online. The
--replicate-* command options to configure
filters can specify a replication channel using the form
For example, suppose channels
channel_2 exist before the server starts,
starting the slave with the command line options
would result in:
Global replication filters: do_db=db1,db3, ignore_db=db4
Channel specific filters on channel_1: do_db=db2 ignore_db=db4
Channel specific filters on channel_2: do_db=db1,db3 ignore_db=db5
The replication filter related command options can take an
channel followed by a
colon, followed by the filter specification. The first colon
is interpreted as a separator, subsequent colons are
interpreted as literal colons. The following command options
support channel specific replication filters using this
If you use a colon but do not specify a
channel for the filter option, for
the option configures the replication filter for the default
replication channel. The default replication channel is the
replication channel which always exists once replication has
been started, and differs from multi-source replication
channels which you create manually. When neither the colon nor
channel is specified the option
configures the global replication filters, for example
configures the global
If you configure multiple
options with the same
database, all filters are added together (put into the
rewrite_do list) and the first one takes
In addition to the
replication filters can be configured using the
CHANGE REPLICATION FILTER
statement. This removes the need to restart the server, but
the slave applier thread must be stopped while making the
change. To make this statement apply the filter to a specific
channel, use the
CHANGE REPLICATION FILTER REPLICATE_DO_DB=(db1) FOR CHANNEL channel_1;
FOR CHANNEL clause is provided, the
statement acts on the specified channel's replication
filters. If multiple types of filters
wild_do_table, and so on) are specified,
only the specified filter types are replaced by the statement.
In a replication topology with multiple channels, for example
on a multi-source replication slave, when no
CHANNEL clause is provided, the statement acts on
the global replication filters and all channels’ replication
filters, using a similar logic as the
CHANNEL case. For more information see
Section 22.214.171.124, “CHANGE REPLICATION FILTER Statement”.
When channel specific replication filters have been
configured, you can remove the filter by issuing an empty
filter type statement. For example to remove all
REPLICATE_REWRITE_DB filters from a
replication channel named
CHANGE REPLICATION FILTER REPLICATE_REWRITE_DB=() FOR CHANNEL channel_1;
REPLICATE_REWRITE_DB filters previously
configured, using either command options or
CHANGE REPLICATION FILTER, are
ALL statement removes channel specific replication
filters that were set on channels deleted by the statement.
When the deleted channel or channels are recreated, any global
replication filters specified for the slave are copied to
them, and no channel specific replication filters are applied.