[KUDU-3291] Crash when performing a diff scan after delta flush races with a batch of ops that update the same row

• Type: Bug
• Status: Resolved
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 1.10.0, 1.10.1, 1.11.0, 1.12.0, 1.11.1, 1.13.0, 1.14.0
• Fix Version/s: 1.15.0
• Code Review: https://gerrit.cloudera.org/c/17547
• Assignee: Andrew Wong
• Reporter: Andrew Wong
• Created: 05/Jun/21 06:44
• Updated: 08/Jun/21 18:09
• Resolved: 08/Jun/21 17:21

Description

It's possible to run into the following crash:

F0604 23:20:50.032124 35483072 delta_store.h:153] Check failed: a.delta_store_id == b.delta_store_id (4445773336 vs. 4445771896)
*** Check failure stack trace: ***
*** Aborted at 1622874050 (unix time) try "date -d @1622874050" if you are using GNU date ***
PC: @     0x7fff724b033a __pthread_kill
*** SIGABRT (@0x7fff724b033a) received by PID 69138 (TID 0x1021d6dc0) stack trace: ***
    @     0x7fff725615fd _sigtramp
    @     0x7ffeef948568 (unknown)
    @     0x7fff72437808 abort
    @        0x107920599 google::logging_fail()
    @        0x10791f4cf google::LogMessage::SendToLog()
    @        0x10791fb95 google::LogMessage::Flush()
    @        0x107923c9f google::LogMessageFatal::~LogMessageFatal()
    @        0x107920b29 google::LogMessageFatal::~LogMessageFatal()
    @        0x1009ae07e kudu::tablet::SelectedDeltas::DeltaLessThanFunctor::operator()()
    @        0x1009aa561 std::__1::max<>()
    @        0x10099c740 kudu::tablet::SelectedDeltas::ProcessDelta()
    @        0x10099e719 kudu::tablet::SelectedDeltas::MergeFrom()
    @        0x1009a2b30 kudu::tablet::DeltaPreparer<>::SelectDeltas()
    @        0x10094a545 kudu::tablet::DeltaFileIterator<>::SelectDeltas()
    @        0x10098b10c kudu::tablet::DeltaIteratorMerger::SelectDeltas()
    @        0x10097133f kudu::tablet::DeltaApplier::InitializeSelectionVector()
    @        0x1056df4fb kudu::MaterializingIterator::MaterializeBlock()
    @        0x1056df2d8 kudu::MaterializingIterator::NextBlock()
    @        0x1056d1c5b kudu::MergeIterState::PullNextBlock()
    @        0x1056d5e62 kudu::MergeIterator::RefillHotHeap()
    @        0x1056d4f0b kudu::MergeIterator::Init()
    @        0x1006a413d kudu::tablet::Tablet::Iterator::Init()
    @        0x1002cb3b9 kudu::tablet::DiffScanTest_TestDiffScanAfterDeltaFlush_Test::TestBody()
    @        0x1005f1b88 testing::internal::HandleExceptionsInMethodIfSupported<>()
    @        0x1005f1add testing::Test::Run()
    @        0x1005f2dd0 testing::TestInfo::Run()
    @        0x1005f3807 testing::TestSuite::Run()
    @        0x100601b57 testing::internal::UnitTestImpl::RunAllTests()
    @        0x100601418 testing::internal::HandleExceptionsInMethodIfSupported<>()
    @        0x10060139c testing::UnitTest::Run()
    @        0x100476201 RUN_ALL_TESTS()
    @        0x100475fa8 main

The crash line assumes that all deltas for a given row that have the same timestamp belong in the same delta store, and it uses this assumption to order the deltas in a diff scan.

However, this is not true because, unlike the case for MRS flushes, we don't wait for all ops to finish applying before flushing the DMS. This means that a batch containing multiple updates to the same row may be spread across multiple DMSs if we delta flush while the batch of updates is being applied.