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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