MySql Switching Masters During Failover with log-slave-updates

failoverMySQLreplication

I am still pretty newbie to mysql. This question is regarding promoting slave with option –log-slave-updates to become a master.

The typical schema of promoting slave to master was described in 15.3.6 Switching Masters During Failover. Here you can find very strict steps how to do it :

Run your slaves with the –log-bin option and without –log-slave-updates. The reason for running the slave without –log-slave-updates is to prevent slaves from receiving updates twice in case you cause one of the slaves to become the new master.

Let's say I have the schema like the following (the image was taken from 15.3.5. Improving Replication Performance).

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Where Master 2 is actually a slave with –log-slave-updates and bin-log enabled. I need to enable –log-slave-update in order to save bin-log from the Master 1 to bin-log of Master 2 and then transfer it to all slave. In case of failover I need promote Master 2 to the role of Master 1. But there is a contradiction to the standard MySql failover schema I have –log-slave-updates enabled which can cause a problem.

In your opinion. What the action I should take in order to do this?

Best Answer

The warning about --log-slave-updates will only apply if you had multiple intermediary 'Master/Slave' servers.

The warning is this (my emphasis):

Then it will write updates that it receives from Master to its own binary log. When Slave 2 changes from Master to Slave 1 as its master, it may receive updates from Slave 1 that it has already received from Master

But in your scenario, Slave 2 is not changing masters, it will still point to the same Master 2 server it always was at.

So now, in case of Master 1 failing, you will need to do two things:

  • Make sure your applications point to Master 2
  • Follow the instructions on promoting one of the three slaves to be new Master 2
  • make sure to enable --log-slave-updates on the new Master 2
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