Support Questions
Find answers, ask questions, and share your expertise

HIVE: dropping the table does not remove data

Highlighted

HIVE: dropping the table does not remove data

Explorer

We often drop and recreate Hive tables with new/recalculated data under same table names. However, after longer use I've found that fetching the data from these tables became broken: i.e., count(*) from that table estimates 2k rows, while export using beeline to csv returns >100k rows, most of which are NULL's at the end of the file. Usually, the problem does not repeat itself when trying to recreate the same tables under different names, but I don't think it's a good solution to create hundreds of tables ala table1, ..., table506 to be able to work with the file..

So my question: is there a fix for this? How can we be sure that dropping the old tables also drops the data?

6 REPLIES 6
Highlighted

Re: HIVE: dropping the table does not remove data

Hi @Javert Kirilov!

Could you share the describe formatted output from your table?
And just asking, but its a managed table? Or external?

Highlighted

Re: HIVE: dropping the table does not remove data

Contributor
@Javert Kirilov

When a table is dropped, the data in case of managed tables gets cleaned up. However for an external table only the metadata of the table is cleared and the data still persists as it is in its place. Could you please confirm if you are using managed or external table?

Highlighted

Re: HIVE: dropping the table does not remove data

Explorer

@dthakkar @Vinicius Higa Murakami

As far as I know, the table is not external, it is created by joining multiple other tables. What worries me is that dropping the table takes like 0.5 sec, so it is not obvious that the data is deleted so quickly (haven't checked to make sure yet, to be honest). Further, there were cases when repeating the same select * .. > output.csv (from beeline) returned different number rows! Those extra rows were made of NULL's, that's why I'm guessing that it doesn't manage leftover files well.

Highlighted

Re: HIVE: dropping the table does not remove data

Explorer

@dthakkar @Vinicius Higa Murakami

Lastly, some of the tables, used in constructing the join, are made in pySpark with the following manner:

sqlContext.sql('DROP TABLE IF EXISTS database.example_table_fromPy')
fd_example_table_fromPy.registerTempTable("pivoted_temp")
sqlContext.sql("CREATE TABLE database.example_table_fromPy STORED AS ORC as select * from pivoted_temp")
fd_example_table_fromPy.printSchema()

I'm wondering, whether the file structure imposed by python (or something like that) may be incompatible with hive tables?

Highlighted

Re: HIVE: dropping the table does not remove data

Explorer

Re: HIVE: dropping the table does not remove data

Hey @Javert Kirilov !
Sorry for the long delay, so regarding your issue. If you really need to clean up your data plus structure then to guarantee, I'd drop the table and truncate it.
Now about the issue, it's kinda strange to me. You mentioned that you're using pyspark right? So I made a research here, and saw smtg interesting (not sure if this is your case, as you're using SQLContext).
https://spark.apache.org/docs/1.6.1/sql-programming-guide.html#saving-to-persistent-tables

Anyways, hope this helps you!