HIVE - INSERT OVERWRITE vs DROP TABLE + CREATE TABLE + INSERT INTO

问题

I'm doing some automatic script of few queries in hive and we found that we need time to time clear the data from a table and insert the new one. And we are thinking what could be faster?

INSERT OVERWRITE TABLE SOME_TABLE
    SELECT * FROM OTHER_TABLE;

or is faster to do like this:

DROP TABLE SOME_TABLE;
CREATE TABLE SOME_TABLE (STUFFS);
INSERT INTO TABLE
    SELECT * FROM OTHER_TABLE;

The overhead of running the queries is not an issue. Due to we have the script o creation too. The question is, the INSERT OVERWRITE with billion of rows is faster than DROP + CREATE + INSERT INTO?

回答1:

For maximum speed I would suggest to 1) issue hadoop fs -rm -r -skipTrash table_dir/* first to remove old data fast without putting files into trash because INSERT OVERWRITE will put all files into Trash and for very big table this will take a lot of time. Then 2) do INSERT OVERWRITE command. This will be faster also because you do not need to drop/create table.

UPDATE:

As of Hive 2.3.0 (HIVE-15880), if the table has TBLPROPERTIES ("auto.purge"="true") the previous data of the table is not moved to Trash when INSERT OVERWRITE query is run against the table. This functionality is applicable only for managed tables. So, INSERT OVERWRITE with auto purge will work faster than rm -skipTrash + INSERT OVERWRITE or DROP+CREATE+INSERT because it will be a single Hive-only command.

回答2:

One edge consideration is that if your schema changes, INSERT OVERWRITE will fail, while DROP+CREATE+INSERT will not. While this is unlikely to apply in most scenarios, if you're prototyping workflow/table schemas then it might be worth considering.

来源：https://stackoverflow.com/questions/39618624/hive-insert-overwrite-vs-drop-table-create-table-insert-into

标签

Hive

create-table