问题
I have a few Hive tables that i am bringing in from RDBMS using Sqoop incremental imports every hour and staging them. I am joining these tables and creating new dimension tables. Whenever i bring in new rows from RDBMS into Hive staging tables, I have to refresh the dimension tables. If there are no new rows, the refresh of dim tables should not be done. The hive version I'm using does not have ACID features.
Need some advice on how this could be achieved in hive.
回答1:
You can INSERT new data in existing Hive tables, like any other database. And Hive also supports the WHERE NOT EXISTS clause.
INSERT INTO TABLE MyDim
SELECT Id, Blah1, Blah2
FROM MySource s
WHERE NOT EXISTS
(SELECT 1 FROM MyDim z WHERE z.Id =s.Id)
But there is a catch: each INSERT will create a new HDFS file, even when there are zero records involved. Too much fragmentation will reduce performance over time.
A weekly "compaction" job would be helpful (e.g. rename the fragmented table, re-CREATE the table, INSERT OVERWRITE from renamed table, drop renamed)
来源：https://stackoverflow.com/questions/32004374/refresh-one-hive-table-from-another-hive-table