Hello, I would like to ask you about mechanism responsible for data consistency in raidb1 distrubution mode in Sequoia (2.10.10). There isn't much information about this in documentation.
Assumptions: Two sequoia controllers in raidb1 distribution mode (Scheduler set to PassThrough). Each Controller has one MySql backend. I know, that communication protocol between controllers and between controller and backend provides data consistency (especially order is preserved). As far as I know database engine does not guarantee that in high load environment (many read/write operations with table locks on myisam) first query that arrives to the engine is executed earlier then a query that arrives later. Eg. there are lots INSERT and DELETE operations. If INSERT operation was send earlier then DELETE operation, there is no guarantee that engine execute queries in te same order, and after this operation there will be a record that should be deleted. In one database environment it's acceptable problem, but when we use sequoia for data replication to more backends there could be situation where on two different backends databases there will be different data. And it is not acceptable. As far I as I understand documentation pessimisticTransaction scheduler could help (because there is only one write operation in parallel and no limits on read queries). But there is no such option on raidb1 configuration. At the end, my question is: Is there a solution in Sequoia to be sure that on every database backend in raidb1 scenario there are same data? Regards, -- Tomasz Lemański
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