READ-COMMITTED limitation of Galera

[y-tak...@s-style.co.jp]

Hello,

This question is already asked many times, but I want to help.

I understand Galera use "Snapshot Isolation" transaction level, which is special level between REPEATABLE READ and SERIALIZABLE.

http://galeracluster.com/documentation-webpages/isolationlevels.html#cluster-transaction-isolation

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When using Galera Cluster in master-slave mode, all four levels are available to you, to the extend that MySQL supports it. In multi-master mode, however, you can only use the REPEATABLE-READ level.

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A above comment mean,  in multi-master mode,  it is necessary for using "Snapshot Isolation" to set tx_isolation = REPEATABLE-READ, is it alright ?

I don't understand why we can only use the REPEATABLE-READ level, so please help me...

Best regard,