'Drop user' appears to use the TOI method, sometimes failing unnecessarily -- Is this by design, or inadvertant since the query starts with the word 'Drop' ?

[John Thorpe]

Our percona 5.6.34 cluster (galera repl lib 3.19, wsrep 26) config has wsrep_OSU_method = TOI, so that DDL will use TOI.   

But 'Drop user' is not a schema change, yet I sometimes see in the logs that it is treated as such.

From a 3-node cluster last week:

server-db01

2017-02-21 13:40:40 8792 [ERROR] Slave SQL: Error 'Operation DROP USER failed for 'someuser'@'someip'' on query. Default database: ''. Query: 'drop user someuser', Error_code: 1396

2017-02-21 13:40:40 8792 [Warning] WSREP: RBR event 1 Query apply warning: 1, 222000

2017-02-21 13:40:40 8792 [Warning] WSREP: Ignoring error for TO isolated action: source: 12abc789-d9s7-12r6-read-ds9uj8887777 version: 3 local: 0 state: APPLYING flags: 65 conn_id: 1809999 trx_id: -1 seqnos (l: 222313, g: 222000, s: 221999, d: 221999, ts: 1587924343447191)

 

server-db02

2017-02-21 13:40:40 26714 [ERROR] Slave SQL: Error 'Operation DROP USER failed for 'someuser'@'someip'' on query. Default database: ''. Query: 'drop user someuser', Error_code: 1396

2017-02-21 13:40:40 26714 [Warning] WSREP: RBR event 1 Query apply warning: 1, 222000

2017-02-21 13:40:40 26714 [Warning] WSREP: Ignoring error for TO isolated action: source: 12abc789-d9s7-12r6-read-ds9uj8887777 version: 3 local: 0 state: APPLYING flags: 65 conn_id: 1809999 trx_id: -1 seqnos (l: 222314, g: 222000, s: 221999, d: 221999, ts: 1587924343447191)

server-db03

(no related error lines)

[John Thorpe]

Well, on thinking about this a bit more, I expect this is probably done this way because the mysql schema tables are myisam and not transactional.