kangkaisen commented on issue #245: Colocate Join
URL: https://github.com/apache/incubator-doris/issues/245#issuecomment-430946769
 
 
   
   > I think there is no need to add "colocate_with" property when create 
parent table. There is some case that user have already have a table, then they 
need a colocate table.
   > 
   
   **The colocate parent table decide the data distribution for all colocate 
tables in a group, and the default  data distribution couldn't ensure the data 
locall**y,  so we must recreate the colocate parent table. If users want 
migrate normal tables to colocate tables, They could do this work by recreating 
the table with different table name and setting "colocate_with" property, then 
loading the historical data to doris, finally renaming the colocate table and 
update the "colocate_with" property.
   
   > All partition have same Bucket Seqs, this will lead to all partition data 
must save to same BE. If partition have three buckets, however there are 100 BE 
in the cluster, then table's data can be located in this 3 BEs. Can this locate 
method be improved?
   > 
   
   Yes, **this is a colocate join internal drawback**. If the cluster node is 
hundreds of and the table data is huge, the user could set the large bucket 
number to ease this problem.
   
   > And different partition can have different buckets, If user change number 
of buckets, the locate map need changed too.
   
   Yes, **Colocate tables could not change the bucket number in order to keep 
data locally.**
   

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