[IMPALA-10422] EXPLAIN statements leak ACID transactions and locks

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: Impala 4.0.0
• Epic Color: ghx-label-4
• Assignee: Zoltán Borók-Nagy
• Reporter: Zoltán Borók-Nagy
• Created: 05/Jan/21 11:56
• Updated: 14/Jan/21 10:29
• Resolved: 06/Jan/21 09:42

Description

Currently EXPLAIN statements might open ACID transactions and create locks on ACID tables.

This is not necessary since we won't modify the table. But the real problem is that these transactions and locks are leaked and open forever. They are even getting heartbeated while the coordinator is still running.

The solution should be to not consume any ACID resources for EXPLAIN statements.

Reproduction:

create table test (i int) tblproperties('transactional'='true', 'transactional_properties'='insert_only');
explain insert overwrite test values (1);
insert overwrite test values (1);
ERROR: TransactionException: Failed to acquire lock for transaction 1595

Workarounds when dealing with this issue:

• Restart the impala cluster so the heartbeating stops. After a while the Hive AcidHouseKeeperService should cleanup the resources (abort the transaction and clear the locks)
• Manually abort the open transaction via Hive with the ABORT TRANSACTIONS <transaction-id>; command. One can find the transaction id with the help of the SHOW LOCKS and SHOW TRANSACTIONS Hive commands.