[IMPALA-11803] impalad hit DCHECK when running union on empty table with MT_DOP>1

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: Impala 4.3.0
• Epic Color: ghx-label-4
• Assignee: Pranav Yogi Lodha
• Reporter: Quanlong Huang
• Created: 16/Dec/22 06:54
• Updated: 28/May/23 13:31
• Resolved: 28/May/23 13:31

Description

This is reported from a community user. When using the DEBUG build, impalad could hit DCHECK and crash when running union with empty table with MT_DOP>1.

I can reproduce the issue by launching the impala cluster with only one node:

bin/start-impala-cluster.py -r -s 1

Then run the following queries

create table empty_tbl (id int) stored as parquet;

create table tbl (id int) stored as parquet;
insert into tbl values (0), (1), (2);
insert into tbl values (3);

set mt_dop=2;
select count(*) from (select * from empty_tbl union all select * from tbl) t;

The stacktrace in impalad.ERROR:

F1216 14:51:44.285214 24142 hdfs-scan-node-base.cc:352] b444e7823f021f02:5af2aa4700000000] Check failed: shared_state_.use_mt_scan_node_ || instance_ctx_pbs.size() == 1 Non MT scan node should only have a single instance.
*** Check failure stack trace: *** 
    @          0x379c53d  google::LogMessage::Fail()
    @          0x379e474  google::LogMessage::SendToLog()
    @          0x379bf1c  google::LogMessage::Flush()
    @          0x379e999  google::LogMessageFatal::~LogMessageFatal()
    @          0x197ddfd  impala::HdfsScanPlanNode::ProcessScanRangesAndInitSharedState()
    @          0x197ef4f  impala::HdfsScanPlanNode::Init()
    @          0x1961150  _ZN6impala8PlanNode16CreateTreeHelperEPNS_13FragmentStateERKSt6vectorINS_9TPlanNodeESaIS4_EEPS0_PiPS9_.localalias
    @          0x1961082  _ZN6impala8PlanNode16CreateTreeHelperEPNS_13FragmentStateERKSt6vectorINS_9TPlanNodeESaIS4_EEPS0_PiPS9_.localalias
    @          0x1961082  _ZN6impala8PlanNode16CreateTreeHelperEPNS_13FragmentStateERKSt6vectorINS_9TPlanNodeESaIS4_EEPS0_PiPS9_.localalias
    @          0x1961205  impala::PlanNode::CreateTree()
    @          0x13c56c2  impala::FragmentState::Init()
    @          0x13c76b9  impala::FragmentState::CreateFragmentStateMap()
    @          0x134492e  impala::QueryState::StartFInstances()
    @          0x1335036  impala::QueryExecMgr::ExecuteQueryHelper()
    @          0x1336100  boost::detail::function::void_function_obj_invoker0<>::invoke()
    @          0x18c7018  impala::Thread::SuperviseThread()
    @          0x18c7e21  boost::detail::thread_data<>::run()
    @          0x239bb77  thread_proxy
    @     0x7effc4fcf6db  start_thread
    @     0x7effc1d6f61f  clone