totalo commented on pull request #10840:
URL: https://github.com/apache/shardingsphere/pull/10840#issuecomment-867579005


   > 3\. ng methods? Can on
   
   For the first point, I understand that the rules used in the 
Schemabuilder#build method are from the upper layer Map<String, Collection< 
RuleConfigs >> SchemarUleConfigs, His key is schemName.
   
   > 3\. ShardingTableMetaDataBuilder
   
   hi , @Beyondeclipse  @tristaZero 
   For 1, I understand that the rules used in the `Schemabuilder#build` method 
are from the upper layer `Map<String, Collection< RuleConfigs >> 
SchemarUleConfigs,` His key is `schemName`.
   
   For 2.a, I think looking at each loader separately, one gets 
`SchemaMetadata` about some attributes of the schema such as the table, and the 
other gets `TableMetadata`. You can see that TableMetadata is more about some 
attribute values of each column in the table. And the bottom implementation of 
the TableTableBuilder is also `ColumnMetadateLoader`. In this scenario,I think. 
Do not use the` SchemaMetaDataLoader loadAllTableNames`, also can meet, but 
there is a risk that has been loaded table repeat live load.
   for 2.b, I agree with you, but the explanation I can think of is that we 
need to query each `DataNode`, so multithreading may be faster.
   The above is my understanding, not sure whether it is correct or not, but 
also hope to correct. 😸.


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