Activiti 创建23张表时 报错：Specified key was too long; max key length is 767 bytes

org.activiti.engine.ActivitiException: couldn't create db schema: create table ACT_RU_EXECUTION ( 
ID_ varchar(64), 
REV_ integer, 
PROC_INST_ID_ varchar(64), 
BUSINESS_KEY_ varchar(255), 
PARENT_ID_ varchar(64), 
PROC_DEF_ID_ varchar(64), 
SUPER_EXEC_ varchar(64), 
ACT_ID_ varchar(255), 
IS_ACTIVE_ TINYINT, 
IS_CONCURRENT_ TINYINT, 
IS_SCOPE_ TINYINT, 
IS_EVENT_SCOPE_ TINYINT, 
SUSPENSION_STATE_ integer, 
CACHED_ENT_STATE_ integer, 
primary key (ID_), 
unique ACT_UNIQ_RU_BUS_KEY (PROC_DEF_ID_, BUSINESS_KEY_) 
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE utf8_bin
at org.activiti.engine.impl.db.DbSqlSession.executeSchemaResource(DbSqlSession.java:954)
at org.activiti.engine.impl.db.DbSqlSession.executeSchemaResource(DbSqlSession.java:879)
at org.activiti.engine.impl.db.DbSqlSession.executeMandatorySchemaResource(DbSqlSession.java:696)
at org.activiti.engine.impl.db.DbSqlSession.dbSchemaCreateEngine(DbSqlSession.java:673)
at org.activiti.engine.impl.db.DbSqlSession.dbSchemaUpdate(DbSqlSession.java:731)
at org.activiti.engine.impl.db.DbSqlSession.performSchemaOperationsProcessEngineBuild(DbSqlSession.java:1013)
at org.activiti.engine.impl.SchemaOperationsProcessEngineBuild.execute(SchemaOperationsProcessEngineBuild.java:25)
at org.activiti.engine.impl.interceptor.CommandExecutorImpl.execute(CommandExecutorImpl.java:24)
at org.activiti.engine.impl.interceptor.CommandContextInterceptor.execute(CommandContextInterceptor.java:61)
at org.activiti.engine.impl.interceptor.LogInterceptor.execute(LogInterceptor.java:37)
at org.activiti.engine.impl.ProcessEngineImpl.<init>(ProcessEngineImpl.java:76)
at org.activiti.engine.impl.cfg.ProcessEngineConfigurationImpl.buildProcessEngine(ProcessEngineConfigurationImpl.java:365)
at junit.ActivitiTest.createTable(ActivitiTest.java:30)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
Caused by: com.mysql.jdbc.exceptions.MySQLSyntaxErrorException: Specified key was too long; max key length is 767 bytes
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:936)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2985)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1631)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1723)
at com.mysql.jdbc.Connection.execSQL(Connection.java:3277)
at com.mysql.jdbc.Connection.execSQL(Connection.java:3206)
at com.mysql.jdbc.Statement.execute(Statement.java:727)
at org.activiti.engine.impl.db.DbSqlSession.executeSchemaResource(DbSqlSession.java:928)
... 35 more