[GitHub] [shardingsphere] sandynz commented on issue #12485: [DistSQL][Scaling] `ScalingAPIFactory.getScalingAPI()` exception when scaling feature not enabled should be optimized to support new RALUpdater implementation

[GitBox <gi...@apache.org>]

sandynz commented on issue #12485:
URL: https://github.com/apache/shardingsphere/issues/12485#issuecomment-922212306


   Verification:
   scaling feature not enabled in `server.yaml`
   
   ### Test with old code:
   ```
   mysql> show scaling job list;
   ERROR 1999 (C1999): Unknown exception: [Scaling server configuration is required.]
   ```
   As new added DistSQL, it will show scaling error, which is wrong.
   
   Exception:
   ```
   [ShardingSphere-Command-1] o.a.s.p.f.c.CommandExecutorTask - Exception occur: 
   java.lang.NullPointerException: Scaling server configuration is required.
   	at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:897)
   	at org.apache.shardingsphere.scaling.core.api.ScalingAPIFactory.checkServerConfig(ScalingAPIFactory.java:106)
   	at org.apache.shardingsphere.scaling.core.api.ScalingAPIFactory.access$000(ScalingAPIFactory.java:48)
   	at org.apache.shardingsphere.scaling.core.api.ScalingAPIFactory$ScalingAPIHolder.getInstance(ScalingAPIFactory.java:119)
   	at org.apache.shardingsphere.scaling.core.api.ScalingAPIFactory.getScalingAPI(ScalingAPIFactory.java:56)
   	at org.apache.shardingsphere.scaling.distsql.handler.ShowScalingJobListQueryResultSet.init(ShowScalingJobListQueryResultSet.java:41)
   	at org.apache.shardingsphere.proxy.backend.text.distsql.ral.query.QueryableRALBackendHandler.execute(QueryableRALBackendHandler.java:48)
   	at org.apache.shardingsphere.proxy.backend.text.distsql.ral.query.QueryableRALBackendHandler.execute(QueryableRALBackendHandler.java:37)
   	at org.apache.shardingsphere.proxy.backend.text.SchemaRequiredBackendHandler.execute(SchemaRequiredBackendHandler.java:51)
   	at org.apache.shardingsphere.proxy.frontend.mysql.command.query.text.query.MySQLComQueryPacketExecutor.execute(MySQLComQueryPacketExecutor.java:57)
   	at org.apache.shardingsphere.proxy.frontend.command.CommandExecutorTask.executeCommand(CommandExecutorTask.java:99)
   	at org.apache.shardingsphere.proxy.frontend.command.CommandExecutorTask.run(CommandExecutorTask.java:72)
   	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
   	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
   	at java.lang.Thread.run(Thread.java:748)
   ```
   
   ### After moving `checkServerConfig()` to `ScalingWorker.init`:
   ```
   mysql> show scaling job list;
   ERROR 1999 (C1999): Unknown exception: [null]
   ```
   Exception:
   ```
   [ShardingSphere-Command-1] o.a.s.p.f.c.CommandExecutorTask - Exception occur: 
   java.lang.NullPointerException: null
   	at org.apache.shardingsphere.scaling.core.api.ScalingAPIFactory$ElasticJobAPIHolder.<init>(ScalingAPIFactory.java:157)
   	at org.apache.shardingsphere.scaling.core.api.ScalingAPIFactory$ElasticJobAPIHolder.getInstance(ScalingAPIFactory.java:168)
   	at org.apache.shardingsphere.scaling.core.api.ScalingAPIFactory.getJobStatisticsAPI(ScalingAPIFactory.java:72)
   	at org.apache.shardingsphere.scaling.core.api.impl.ScalingAPIImpl.list(ScalingAPIImpl.java:55)
   	at org.apache.shardingsphere.scaling.distsql.handler.ShowScalingJobListQueryResultSet.init(ShowScalingJobListQueryResultSet.java:41)
   	at org.apache.shardingsphere.proxy.backend.text.distsql.ral.query.QueryableRALBackendHandler.execute(QueryableRALBackendHandler.java:48)
   	at org.apache.shardingsphere.proxy.backend.text.distsql.ral.query.QueryableRALBackendHandler.execute(QueryableRALBackendHandler.java:37)
   	at org.apache.shardingsphere.proxy.backend.text.SchemaRequiredBackendHandler.execute(SchemaRequiredBackendHandler.java:51)
   	at org.apache.shardingsphere.proxy.frontend.mysql.command.query.text.query.MySQLComQueryPacketExecutor.execute(MySQLComQueryPacketExecutor.java:57)
   	at org.apache.shardingsphere.proxy.frontend.command.CommandExecutorTask.executeCommand(CommandExecutorTask.java:99)
   	at org.apache.shardingsphere.proxy.frontend.command.CommandExecutorTask.run(CommandExecutorTask.java:72)
   	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
   	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
   	at java.lang.Thread.run(Thread.java:748)
   ```
   
   There's no error message for user, it's better to keep meaningful error message.
   
   ### Consider other solutions:
   1. Scaling sub-classes of `RALUpdater` invoke `ScalingAPIFactory.getScalingAPI()` on demand, but not when class initialization.
   2. Any sub-class of `RALUpdater` belongs to a feature, if certain feature is not enabled, then `ShardingSphereServiceLoader.register` should ignore to initialize related `RALUpdater` implementation. 
   
   Currently, I'll implement it with solution 1.
   
   @RaigorJiang  Could you have a look at solution 2, is it possible to implement?
   
   


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