This topic provides answers to some frequently asked questions about Impala.

Ten seconds after I use JDBC to query data in Impala 3.4, a message appears, which indicates that the session times out. What do I do?

Run a command on Impala to set the FETCH_ROWS_TIMEOUT_MS parameter to 0. The value 0 indicates that the session is permanently valid. Sample command:
jdbc:impala://impala-hive.ymt.io:21050/ymtcube;FETCH_ROWS_TIMEOUT_MS=0

What do I do if I cannot find newly added Hive tables in Impala?

After you perform operations on table metadata in a component other than Impala, run the INVALIDATE METADATA command on Impala to refresh the metadata of a table or all tables in the database.

Can I change the owner of data when I use Impala to write the data to Hive tables?

No, the owner of the data that is written to Hive tables by using Impala is Impala and cannot be changed.

What parameter is used to specify the memory configuration of an Impala node?

The mem_limit parameter specifies the amount of memory that can be consumed, in percentage. To configure this parameter, perform the following operations: Log on to the EMR console. Go to the Impala service page. Click the Configure tab and search for the mem_limit parameter in the search box of the Configuration Filter section. The default value of the mem_limit parameter is 80%.

How do I specify the maximum size of memory that can be consumed by a single query statement?

Run a command on Impala to configure the mem_limit parameter. For example, set the mem_limit parameter to 10 GB.

How do I improve the efficiency of a query statement that does not contain a JOIN clause?

Run a command on Impala to set the mt_dop parameter to a larger value to improve the parallelism of instances in a fragment.