DatabaseFlushTest is not stable on MariaDB Galera

Expecting:
  <org.camunda.bpm.engine.ProcessEngineException: ENGINE-03004 Exception while executing Database Operation 'INSERT VariableInstanceEntity[1197913]' with message '
### Error flushing statements.  Cause: org.apache.ibatis.executor.BatchExecutorException: org.camunda.bpm.engine.impl.persistence.entity.VariableInstanceEntity.insertVariableInstance (batch index #6) failed. 5 prior sub executor(s) completed successfully, but will be rolled back. Cause: java.sql.BatchUpdateException: (conn:5) Deadlock found when trying to get lock; try restarting transaction
### Cause: org.apache.ibatis.executor.BatchExecutorException: org.camunda.bpm.engine.impl.persistence.entity.VariableInstanceEntity.insertVariableInstance (batch index #6) failed. 5 prior sub executor(s) completed successfully, but will be rolled back. Cause: java.sql.BatchUpdateException: (conn:5) Deadlock found when trying to get lock; try restarting transaction'. Flush summary: 
 [
  INSERT HistoricVariableInstanceEntity[1197913]
  INSERT HistoricVariableInstanceEntity[1197915]
  INSERT HistoricVariableInstanceEntity[1197917]
  INSERT HistoricVariableUpdateEventEntity[1197914]
  INSERT HistoricVariableUpdateEventEntity[1197916]
  INSERT HistoricVariableUpdateEventEntity[1197918]
  INSERT HistoricTaskInstanceEventEntity[1197927]
  INSERT HistoricActivityInstanceEventEntity[task2-2:1197925]
  INSERT TaskEntity[1197927]
  INSERT VariableInstanceEntity[1197913]
  INSERT VariableInstanceEntity[1197915]
  INSERT VariableInstanceEntity[1197917]
  DELETE TaskEntity[1197912]
  UPDATE ExecutionEntity[1197908]
  UPDATE ExecutionEntity[1197904]
  UPDATE HistoricActivityInstanceEventEntity[task2-1:1197911]
  UPDATE HistoricTaskInstanceEventEntity[1197912]
]>
to be an instance of:
  <org.camunda.bpm.engine.OptimisticLockingException>
but was:
  <"org.camunda.bpm.engine.ProcessEngineException: ENGINE-03004 Exception while executing Database Operation 'INSERT VariableInstanceEntity[1197913]' with message '
### Error flushing statements.  Cause: org.apache.ibatis.executor.BatchExecutorException: org.camunda.bpm.engine.impl.persistence.entity.VariableInstanceEntity.insertVariableInstance (batch index #6) failed. 5 prior sub executor(s) completed successfully, but will be rolled back. Cause: java.sql.BatchUpdateException: (conn:5) Deadlock found when trying to get lock; try restarting transaction
### Cause: org.apache.ibatis.executor.BatchExecutorException: org.camunda.bpm.engine.impl.persistence.entity.VariableInstanceEntity.insertVariableInstance (batch index #6) failed. 5 prior sub executor(s) completed successfully, but will be rolled back. Cause: java.sql.BatchUpdateException: (conn:5) Deadlock found when trying to get lock; try restarting transaction'. Flush summary: 
 [
  INSERT HistoricVariableInstanceEntity[1197913]
  INSERT HistoricVariableInstanceEntity[1197915]
  INSERT HistoricVariableInstanceEntity[1197917]
  INSERT HistoricVariableUpdateEventEntity[1197914]
  INSERT HistoricVariableUpdateEventEntity[1197916]
  INSERT HistoricVariableUpdateEventEntity[1197918]
  INSERT HistoricTaskInstanceEventEntity[1197927]
  INSERT HistoricActivityInstanceEventEntity[task2-2:1197925]
  INSERT TaskEntity[1197927]
  INSERT VariableInstanceEntity[1197913]
  INSERT VariableInstanceEntity[1197915]
  INSERT VariableInstanceEntity[1197917]
  DELETE TaskEntity[1197912]
  UPDATE ExecutionEntity[1197908]
  UPDATE ExecutionEntity[1197904]
  UPDATE HistoricActivityInstanceEventEntity[task2-1:1197911]
  UPDATE HistoricTaskInstanceEventEntity[1197912]
]
 at org.camunda.bpm.engine.impl.db.EnginePersistenceLogger.flushDbOperationException(EnginePersistenceLogger.java:131)
 at org.camunda.bpm.engine.impl.db.entitymanager.DbEntityManager.flushDbOperations(DbEntityManager.java:355)
 at org.camunda.bpm.engine.impl.db.entitymanager.DbEntityManager.flushDbOperationManager(DbEntityManager.java:322)
 at org.camunda.bpm.engine.impl.db.entitymanager.DbEntityManager.flush(DbEntityManager.java:294)
 at org.camunda.bpm.engine.impl.interceptor.CommandContext.flushSessions(CommandContext.java:268)
 at org.camunda.bpm.engine.impl.interceptor.CommandContext.close(CommandContext.java:186)
 at org.camunda.bpm.engine.impl.interceptor.CommandContextInterceptor.execute(CommandContextInterceptor.java:116)
 at org.camunda.bpm.engine.impl.interceptor.ProcessApplicationContextInterceptor.execute(ProcessApplicationContextInterceptor.java:70)
 at org.camunda.bpm.engine.impl.interceptor.LogInterceptor.execute(LogInterceptor.java:33)
 at org.camunda.bpm.engine.test.concurrency.ConcurrencyTestCase$1.run(ConcurrencyTestCase.java:62)
 at java.lang.Thread.run(Thread.java:745)
Caused by: org.apache.ibatis.exceptions.PersistenceException: 
### Error flushing statements.  Cause: org.apache.ibatis.executor.BatchExecutorException: org.camunda.bpm.engine.impl.persistence.entity.VariableInstanceEntity.insertVariableInstance (batch index #6) failed. 5 prior sub executor(s) completed successfully, but will be rolled back. Cause: java.sql.BatchUpdateException: (conn:5) Deadlock found when trying to get lock; try restarting transaction
### Cause: org.apache.ibatis.executor.BatchExecutorException: org.camunda.bpm.engine.impl.persistence.entity.VariableInstanceEntity.insertVariableInstance (batch index #6) failed. 5 prior sub executor(s) completed successfully, but will be rolled back. Cause: java.sql.BatchUpdateException: (conn:5) Deadlock found when trying to get lock; try restarting transaction
 at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
 at org.apache.ibatis.session.defaults.DefaultSqlSession.flushStatements(DefaultSqlSession.java:255)
 at org.camunda.bpm.engine.impl.db.sql.DbSqlSession.flushBatchOperations(DbSqlSession.java:320)
 at org.camunda.bpm.engine.impl.db.sql.BatchDbSqlSession.executeDbOperations(BatchDbSqlSession.java:67)
 at org.camunda.bpm.engine.impl.db.entitymanager.DbEntityManager.flushDbOperations(DbEntityManager.java:339)
 ... 9 more
Caused by: org.apache.ibatis.executor.BatchExecutorException: org.camunda.bpm.engine.impl.persistence.entity.VariableInstanceEntity.insertVariableInstance (batch index #6) failed. 5 prior sub executor(s) completed successfully, but will be rolled back. Cause: java.sql.BatchUpdateException: (conn:5) Deadlock found when trying to get lock; try restarting transaction
 at org.apache.ibatis.executor.BatchExecutor.doFlushStatements(BatchExecutor.java:146)
 at org.apache.ibatis.executor.BaseExecutor.flushStatements(BaseExecutor.java:129)
 at org.apache.ibatis.executor.BaseExecutor.flushStatements(BaseExecutor.java:122)
 at org.apache.ibatis.executor.CachingExecutor.flushStatements(CachingExecutor.java:114)
 at org.apache.ibatis.session.defaults.DefaultSqlSession.flushStatements(DefaultSqlSession.java:253)
 ... 12 more
Caused by: java.sql.BatchUpdateException: (conn:5) Deadlock found when trying to get lock; try restarting transaction
 at org.mariadb.jdbc.MariaDbStatement.executeBatchExceptionEpilogue(MariaDbStatement.java:298)
 at org.mariadb.jdbc.MariaDbPreparedStatementClient.executeBatch(MariaDbPreparedStatementClient.java:290)
 at org.apache.ibatis.executor.BatchExecutor.doFlushStatements(BatchExecutor.java:122)
 ... 16 more
Caused by: java.sql.SQLTransactionRollbackException: (conn:5) Deadlock found when trying to get lock; try restarting transaction
 at org.mariadb.jdbc.internal.util.exceptions.ExceptionMapper.get(ExceptionMapper.java:160)
 at org.mariadb.jdbc.internal.util.exceptions.ExceptionMapper.getException(ExceptionMapper.java:118)
 at org.mariadb.jdbc.MariaDbStatement.executeBatchExceptionEpilogue(MariaDbStatement.java:295)
 ... 18 more
Caused by: java.sql.SQLException: Deadlock found when trying to get lock; try restarting transaction
Query is: insert into ACT_RU_VARIABLE
    (
      ID_,
      TYPE_,
      NAME_,
      PROC_INST_ID_,
      EXECUTION_ID_,
      CASE_INST_ID_,
      CASE_EXECUTION_ID_,
      TASK_ID_,
      BYTEARRAY_ID_,
      DOUBLE_,
      LONG_,
      TEXT_,
      TEXT2_,
      VAR_SCOPE_,
      SEQUENCE_COUNTER_,
      IS_CONCURRENT_LOCAL_,
      TENANT_ID_,
      REV_
    )
    values (
      '1197913',
      'string',
      'key3',
      '1197904',
      '1197904',
      <null>,
      <null>,
      <null>,
      <null>,
      <null>,
      <null>,
      'val3',
      <null>,
      '1197904',
      1,
      0,
      <null>,
      1
    )
 at org.mariadb.jdbc.internal.util.LogQueryTool.exceptionWithQuery(LogQueryTool.java:112)
 at org.mariadb.jdbc.internal.protocol.AbstractQueryProtocol$1.handleResultException(AbstractQueryProtocol.java:306)
 at org.mariadb.jdbc.internal.protocol.AsyncMultiRead.call(AsyncMultiRead.java:139)
 at org.mariadb.jdbc.internal.protocol.AsyncMultiRead.call(AsyncMultiRead.java:67)
 at java.util.concurrent.FutureTask.run(FutureTask.java:262)
 at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
 at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
 ... 1 more
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