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replication topologies

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Giuseppe Maxia edited this page Nov 6, 2020 · 2 revisions

Replication topologies

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Multiple sandboxes can be deployed using replication with several topologies (using dbdeployer deploy replication --topology=xxxxx:

  • master-slave is the default topology. It will install one master and two slaves. More slaves can be added with the option --nodes.
  • group will deploy three peer nodes in group replication. If you want to use a single primary deployment, add the option --single-primary. Available for MySQL 5.7 and later.
  • fan-in is the opposite of master-slave. Here we have one slave and several masters. This topology requires MySQL 5.7 or higher.
  • all-masters is a special case of fan-in, where all nodes are masters and are also slaves of all nodes.

It is possible to tune the flow of data in multi-source topologies. The default for fan-in is three nodes, where 1 and 2 are masters, and 2 are slaves. You can change the predefined settings by providing the list of components:

$ dbdeployer deploy replication --topology=fan-in \
    --nodes=5 --master-list="1,2 3" \
    --slave-list="4,5" 8.0.4 \
    --concurrent

In the above example, we get 5 nodes instead of 3. The first three are master (--master-list="1,2,3") and the last two are slaves (--slave-list="4,5") which will receive data from all the masters. There is a test automatically generated to check the replication flow. In our case it shows the following:

$ ~/sandboxes/fan_in_msb_8_0_4/test_replication
# master 1
# master 2
# master 3
# slave 4
ok - '3' == '3' - Slaves received tables from all masters
# slave 5
ok - '3' == '3' - Slaves received tables from all masters
# pass: 2
# fail: 0

The first three lines show that each master has done something. In our case, each master has created a different table. Slaves in nodes 5 and 6 then count how many tables they found, and if they got the tables from all masters, the test succeeds.

Two more topologies, ndb and pxc require binaries of dedicated flavors, respectively MySQL Cluster and Percona Xtradb Cluster. dbdeployer detects whether an expanded tarball satisfies the flavor requirements, and deploys only when the criteria are met.

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