question about ddl on galera

[周彦伟]

 hiI am user of Percona Xtradb Cluster，and find a question when executing ddl statement on one node of a pxc cluster, The ddl will kill all querys on all node include select which use the modified table. But this is  rude obviously。The select query can be killed，but DML is not.

I have an idea about it。Before do the WSREP_TO_ISOLATION_BEGIN  ，we add  a MDL_SHARED_NO_WRITE type

MDL on the table。This can avoid enter the TOI unconditional util it get the MDL lock。

But It can raise deadlock when multi-master write. But it is ok where single-node writed.

I no sure  whether it is ok, so I want to ask for your  advise.

thank you

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                             周彦伟
                             zhouy...@gmail.com