Hey,brother. Glad to hear from you!I think we can use limit/offset(if the database support this operation),or we can use sub-selection(if the database does not support limint/offset) For example: For MySQL:select * from table limiit 0,5;select * from table limit 6,10... For Oracle we can use rownum I just can not understand why sqoop override this opreation above.This override can lead to data skew. From: Abraham Elmahrek Date: 2014-09-10 00:38 To: [email protected] Subject: Re: the confusion of --split-by parameter Hey there,
For databases, there needs to be a way to actually infer boundaries for a particular column. Simply performing a "select *" would not be enough because we would not know how to query the database. -Abe On Mon, Sep 8, 2014 at 8:33 PM, [email protected] <[email protected]> wrote: Hi,all. In sqoop we can specify the parameter --split-by,which can determine which field we will use to split map recored. But if the split field's data is skew.The workload between maps will be imbalance.I want to know why sqoop does not use select count(*) from table/num-maps to determine each map's workload.As I know some other base class of DataDrivenDBInputFormat's has the implementation of select count(*) from table/num-maps.Then why sqoop override this.
