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How Does: ScaleArc handle 'read_only' parameter during Percona DB Fail-over?

How Does: ScaleArc handle 'read_only' parameter during Percona DB Fail-over?


Release Classification Level DB Platform Categories
v3.11 How To

MySQL/Percona Fail-over


  • Does ScaleArc's Failover logic consider 'read_only' parameter for each database? 
  • Which of the ScaleArc logs has this captured?
  • Yes. ScaleArc's Failover script will consider "read_only" variable and flip it prior to promotion or demotion during the failover.
    For instance, if your Slave has "read_only" variable ON -->

mysql> show global variables like 'read%only';
| Variable_name | Value |
| read_only     | ON    |
1 row in set (0.01 sec)

Then during failover, ScaleArc will change it to 'OFF' prior to promoting it to an R/W server.

Likewise, for an R/W server, it will be turned 'ON' prior to demoting it to be a Slave.

  • This change in parameter is captured in following log -->


2017-05-15 16:47:45,206 INFO UnSetting Read_Only Flag for new promoted server // Unsetting Read only flag to new RW 
2017-05-15 16:47:48,484 INFO SET Query is SET GLOBAL READ_ONLY=1 and response is None // Setting read only flag to new ST+ Read Server.
2017-05-15 16:47:48,489 INFO SHOW_VARIABLES Query is show variables like 'read_only'; and response is {'Value': 'ON', 'Variable_name': 'read_only'} and is_read_only_present is True
2017-05-15 16:47:48,489 INFO Successfully Change ReadOnly Flag value is True

Note : This behavior is same as in a native MySQL Master/Slave setup within ScaleArc, with "AUTO FAILOVER > Replication Type = Synchronous".

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