(gdb) bt full
#0  0x00007f87d9d8e207 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:55
        resultvar = 0
        pid = 8111
        selftid = 8171
#1  0x00007f87d9d8f8f8 in __GI_abort () at abort.c:90
        save_stage = 2
        act = {__sigaction_handler = {sa_handler = 0xfffdd6, sa_sigaction = 0xfffdd6}, sa_mask = {__val = {16777050, 0, 0, 0, 0, 1, 140221455921731, 140221455905696, 140221452466382, 140221455921600, 10, 140219273709920, 0, 140219894360864, 
              140221452467651, 140221455921600}}, sa_flags = -630313968, sa_restorer = 0x10bb0d0 <stderr>}
        sigs = {__val = {32, 0 <repeats 15 times>}}
#2  0x00007f87da6d863c in __gnu_cxx::__verbose_terminate_handler () at /tmp/deploy/objdir/../gcc-10.2.0/libstdc++-v3/libsupc++/vterminate.cc:95
        terminating = false
        t = <optimized out>
#3  0x0000000000b69f2b in backtrace_terminate_handler() () at /home/couchbase/jenkins/workspace/toy-unix-simple/kv_engine/utilities/terminate_handler.cc:88
No locals.
#4  0x00007f87da6e38f6 in __cxxabiv1::__terminate(void (*)()) () at /tmp/deploy/objdir/../gcc-10.2.0/libstdc++-v3/libsupc++/eh_terminate.cc:48
No locals.
#5  0x00007f87da6e3961 in std::terminate () at /tmp/deploy/objdir/../gcc-10.2.0/libstdc++-v3/libsupc++/eh_terminate.cc:58
No locals.
#6  0x00007f87da6e3bf4 in __cxxabiv1::__cxa_throw (obj=obj@entry=0x7f8758000940, tinfo=tinfo@entry=0xc7c5b8 <typeinfo for gsl::fail_fast>, dest=dest@entry=0x5a0440 <gsl::fail_fast::~fail_fast()>)
    at /tmp/deploy/objdir/../gcc-10.2.0/libstdc++-v3/libsupc++/eh_throw.cc:95
        globals = <optimized out>
        header = 0x7f87580008c0
#7  0x0000000000451953 in gsl::detail::fail_fast_throw (message=0xcc3728 "GSL: Precondition failure: 'itemsForCursor.ranges.size() == 1' at /home/couchbase/jenkins/workspace/toy-unix-simple/kv_engine/engines/ep/src/dcp/active_stream.cc:1012")
    at /home/couchbase/jenkins/workspace/toy-unix-simple/third_party/gsl-lite/include/gsl/gsl-lite.hpp:1769
No locals.
#8  0x00000000004ec996 in ActiveStream::getOutstandingItems (this=0x7f85b0be3290, vb=...) at /home/couchbase/jenkins/workspace/toy-unix-simple/kv_engine/engines/ep/src/dcp/active_stream.cc:1025
        range = <optimized out>
        result = {checkpointType = Disk, historical = No, items = std::vector of length 0, capacity 0, 
          diskCheckpointState = {<std::_Optional_base<ActiveStream::OutstandingItemsResult::DiskCheckpointState, true, true>> = {<std::_Optional_base_impl<ActiveStream::OutstandingItemsResult::DiskCheckpointState, std::_Optional_base<ActiveStream::OutstandingItemsResult::DiskCheckpointState, true, true> >> = {<No data fields>}, _M_payload = {<std::_Optional_payload_base<ActiveStream::OutstandingItemsResult::DiskCheckpointState>> = {_M_payload = {_M_empty = {<No data fields>}, _M_value = {
                      highCompletedSeqno = 553195}}, 
                  _M_engaged = false}, <No data fields>}}, <std::_Enable_copy_move<true, true, true, true, std::optional<ActiveStream::OutstandingItemsResult::DiskCheckpointState> >> = {<No data fields>}, <No data fields>}, visibleSeqno = 0, 
          ranges = std::vector of length 0, capacity 0}
        itemsForCursor = {ranges = std::vector of length 0, capacity 0, moreAvailable = false, checkpointType = Disk, historical = Yes, 
          maxDeletedRevSeqno = {<std::_Optional_base<unsigned long, true, true>> = {<std::_Optional_base_impl<unsigned long, std::_Optional_base<unsigned long, true, true> >> = {<No data fields>}, 
              _M_payload = {<std::_Optional_payload_base<unsigned long>> = {_M_payload = {_M_empty = {<No data fields>}, _M_value = 998}, 
                  _M_engaged = true}, <No data fields>}}, <std::_Enable_copy_move<true, true, true, true, std::optional<unsigned long> >> = {<No data fields>}, <No data fields>}, 
          highCompletedSeqno = {<std::_Optional_base<unsigned long, true, true>> = {<std::_Optional_base_impl<unsigned long, std::_Optional_base<unsigned long, true, true> >> = {<No data fields>}, 
              _M_payload = {<std::_Optional_payload_base<unsigned long>> = {_M_payload = {_M_empty = {<No data fields>}, _M_value = 553195}, 
                  _M_engaged = true}, <No data fields>}}, <std::_Enable_copy_move<true, true, true, true, std::optional<unsigned long> >> = {<No data fields>}, <No data fields>}, visibleSeqno = 628628, Python Exception <class 'gdb.error'> There is no member or method named _M_head_impl.: 
maxCas = 0, flushHandle = }
#9  0x00000000008fe2be in ActiveStream::nextCheckpointItemTask(std::lock_guard<std::mutex> const&) () at /home/couchbase/jenkins/workspace/toy-unix-simple/kv_engine/engines/ep/src/dcp/active_stream.cc:982
        res = {checkpointType = Disk, historical = No, items = std::vector of length 0, capacity 0, 
          diskCheckpointState = {<std::_Optional_base<ActiveStream::OutstandingItemsResult::DiskCheckpointState, true, true>> = {<std::_Optional_base_impl<ActiveStream::OutstandingItemsResult::DiskCheckpointState, std::_Optional_base<ActiveStream::OutstandingItemsResult::DiskCheckpointState, true, true> >> = {<No data fields>}, _M_payload = {<std::_Optional_payload_base<ActiveStream::OutstandingItemsResult::DiskCheckpointState>> = {_M_payload = {_M_empty = {<No data fields>}, _M_value = {
                      highCompletedSeqno = 553195}}, 
                  _M_engaged = false}, <No data fields>}}, <std::_Enable_copy_move<true, true, true, true, std::optional<ActiveStream::OutstandingItemsResult::DiskCheckpointState> >> = {<No data fields>}, <No data fields>}, visibleSeqno = 0, 
          ranges = std::vector of length 0, capacity 0}
        producer = <error reading variable: Cannot access memory at address 0x7f85eecd6708>
        vbucket = <error reading variable: Cannot access memory at address 0x7f86fae1a708>
#10 0x00000000008fe3f4 in ActiveStream::nextCheckpointItemTask() () at /home/couchbase/jenkins/workspace/toy-unix-simple/kv_engine/engines/ep/src/dcp/active_stream.cc:967
        lh = {_M_device = @0x7f85b0be32f8}
#11 0x0000000000904a39 in ActiveStreamCheckpointProcessorTask::run() () at /home/couchbase/jenkins/workspace/toy-unix-simple/kv_engine/engines/ep/src/dcp/active_stream_checkpoint_processor_task.cc:52
        as = <optimized out>
        rh = {<StreamContainer<std::shared_ptr<ActiveStream> >::Iterable<std::_Fwd_list_const_iterator<std::shared_ptr<ActiveStream> > >> = {itr = {_M_node = 0x7f8740203760}, endItr = {_M_node = 0x0}, before = {_M_node = <optimized out>}}, readLock = {
            _M_pm = 0x7f861bd39878, _M_owns = <optimized out>}, container = <optimized out>}
        streams = <error reading variable: Cannot access memory at address 0x7f861bd39858>
        iterations = 1
        expected = false
#12 0x0000000000ad86c9 in GlobalTask::execute(std::basic_string_view<char, std::char_traits<char> >) () at /home/couchbase/jenkins/workspace/toy-unix-simple/kv_engine/executor/globaltask.cc:98

        guard = {previous = 0x0}
        start = <optimized out>
        runAgain = <optimized out>
#13 0x0000000000ad1d8a in FollyExecutorPool::TaskProxy::scheduleViaCPUPool()::{lambda()#2}::operator()() const (__closure=0x7f877cfe7350) at /home/couchbase/jenkins/workspace/toy-unix-simple/kv_engine/executor/folly_executorpool.cc:309
        runAgain = <optimized out>
---Type <return> to continue, or q <return> to quit---
        proxy = @0x7f87cc06ee10: <error reading variable>
#14 0x0000000000ad9a7e in operator() (this=0x7f877cfe7350) at /home/couchbase/jenkins/workspace/toy-unix-simple/kv_engine/executor/cancellable_cpu_executor.cc:42
        fn = @0x7f877cfe7350: {<folly::detail::function::FunctionTraits<void()>> = {<No data fields>}, data_ = {big = 0x7f87cc06ee10, tiny = {
              __data = "\020\356\006\314\207\177\000\000@t\376|\207\177\000\000\000\000\000\000\000\000\000\000\300q`\330\207\177\000\000y\004\000\000\000\000\000\000}\204\302\000\000\000\000", __align = {<No data fields>}}}, 
          call_ = 0xad22c0 <folly::detail::function::FunctionTraits<void ()>::callSmall<FollyExecutorPool::TaskProxy::scheduleViaCPUPool()::{lambda()#2}>(folly::detail::function::Data&)>, 
          exec_ = 0xad07b0 <folly::detail::function::execSmall<FollyExecutorPool::TaskProxy::scheduleViaCPUPool()::{lambda()#2}>(folly::detail::function::Op, folly::detail::function::Data*, folly::detail::function::Data)>}
#15 CancellableCPUExecutor::add(GlobalTask*, folly::Function<void ()>)::{lambda()#1}::operator()() const () at /home/couchbase/jenkins/workspace/toy-unix-simple/kv_engine/executor/cancellable_cpu_executor.cc:42
        task = {storage_ = {{emptyState = -128 '\200', value = {task = 0x7f85dc14c780, func = {<folly::detail::function::FunctionTraits<void()>> = {<No data fields>}, data_ = {big = 0x7f87cc06ee10, tiny = {
                      __data = "\020\356\006\314\207\177\000\000@t\376|\207\177\000\000\000\000\000\000\000\000\000\000\300q`\330\207\177\000\000y\004\000\000\000\000\000\000}\204\302\000\000\000\000", __align = {<No data fields>}}}, 
                  call_ = 0xad22c0 <folly::detail::function::FunctionTraits<void ()>::callSmall<FollyExecutorPool::TaskProxy::scheduleViaCPUPool()::{lambda()#2}>(folly::detail::function::Data&)>, 
                  exec_ = 0xad07b0 <folly::detail::function::execSmall<FollyExecutorPool::TaskProxy::scheduleViaCPUPool()::{lambda()#2}>(folly::detail::function::Op, folly::detail::function::Data*, folly::detail::function::Data)>}}}, hasValue = true}}
        this = <optimized out>
#16 0x0000000000c37a50 in operator() (this=0x7f877cfe7540) at /home/couchbase/jenkins/cbdeps-ws/deps/packages/build/folly/folly-prefix/src/folly/folly/Function.h:416
        fn = @0x7f877cfe7540: {<folly::detail::function::FunctionTraits<void()>> = {<No data fields>}, data_ = {big = 0x7f87d858bc00, tiny = {
              __data = "\000\274X\330\207\177\000\000\320\247\264\334\207\177\000\000\060\000\000\000\000\000\000\000\353\037\000\000\000\000\000\000\350\000\000\000\000\000\000\000\020v\376|\207\177\000", __align = {<No data fields>}}}, 
          call_ = 0xad9e00 <folly::detail::function::FunctionTraits<void()>::callSmall<CancellableCPUExecutor::add(GlobalTask*, folly::Func)::<lambda()> >(folly::detail::function::Data &)>, 
          exec_ = 0xad93b0 <folly::detail::function::execSmall<CancellableCPUExecutor::add(GlobalTask*, folly::Func)::<lambda()> >(folly::detail::function::Op, folly::detail::function::Data *, folly::detail::function::Data *)>}
#17 folly::ThreadPoolExecutor::runTask(std::shared_ptr<folly::ThreadPoolExecutor::Thread> const&, folly::ThreadPoolExecutor::Task&&) (this=this@entry=0x7f87d858bd00, thread=<error reading variable: Cannot access memory at address 0x7f87d965f8b8>, 
    task=task@entry=<unknown type in /usr/lib/debug/opt/couchbase/bin/memcached-7.2.1-17234.x86_64.debug, CU 0xac1bf97, DIE 0xac9fecc>)
    at /home/couchbase/jenkins/cbdeps-ws/deps/packages/build/folly/folly-prefix/src/folly/folly/executors/ThreadPoolExecutor.cpp:97
        rctx = {prev_ = std::shared_ptr (empty) 0x0}
        startTime = {__d = {__r = 8819895638379684}}
        stats = {expired = false, waitTime = {__r = 112509}, runTime = {__r = 0}, enqueueTime = {__d = {__r = 8819895638267175}}, requestId = 0}
#18 0x0000000000c224ea in folly::CPUThreadPoolExecutor::threadRun (this=0x7f87d858bd00, thread=<error reading variable: Cannot access memory at address 0x7f87d965f8b8>)
    at /home/couchbase/jenkins/cbdeps-ws/deps/packages/build/folly/folly-prefix/src/folly/folly/executors/CPUThreadPoolExecutor.cpp:265
        task = {storage_ = {{emptyState = 0 '\000', value = {<folly::ThreadPoolExecutor::Task> = {func_ = {<folly::detail::function::FunctionTraits<void()>> = {<No data fields>}, data_ = {big = 0x7f87d858bc00, tiny = {
                        __data = "\000\274X\330\207\177\000\000\320\247\264\334\207\177\000\000\060\000\000\000\000\000\000\000\353\037\000\000\000\000\000\000\350\000\000\000\000\000\000\000\020v\376|\207\177\000", __align = {<No data fields>}}}, 
                    call_ = 0xad9e00 <folly::detail::function::FunctionTraits<void()>::callSmall<CancellableCPUExecutor::add(GlobalTask*, folly::Func)::<lambda()> >(folly::detail::function::Data &)>, 
                    exec_ = 0xad93b0 <folly::detail::function::execSmall<CancellableCPUExecutor::add(GlobalTask*, folly::Func)::<lambda()> >(folly::detail::function::Op, folly::detail::function::Data *, folly::detail::function::Data *)>}, 
                  enqueueTime_ = {__d = {__r = 8819895638267175}}, expiration_ = {__r = 0}, expireCallback_ = {<folly::detail::function::FunctionTraits<void()>> = {<No data fields>}, data_ = {big = 0x1feb, tiny = {
                        __data = "\353\037\000\000\000\000\000\000\233\212\250", '\000' <repeats 13 times>, "_\356\223\334\207\177\000\000\200\367\376\177\207\177\000\000@\206\264\334\207\177\000", __align = {<No data fields>}}}, call_ = 0x467e0b
     <folly::detail::function::FunctionTraits<void ()>::uninitCall(folly::detail::function::Data&)>, exec_ = 0x0}, context_ = std::shared_ptr (empty) 0x0}, poison = false, priority_ = 0 '\000', queueObserverPayload_ = 140221426091280}}, 
            hasValue = true}}
        guard = {list_ = {forbid = true, prev = 0x0, curr = {name = {static npos = <optimized out>, b_ = 0xcfee73 "CPUThreadPoolExecutor", e_ = 0xcfee88 ""}}}}
#19 0x0000000000c3aa09 in __invoke_impl<void, void (folly::ThreadPoolExecutor::*&)(std::shared_ptr<folly::ThreadPoolExecutor::Thread>), folly::ThreadPoolExecutor*&, std::shared_ptr<folly::ThreadPoolExecutor::Thread>&> (__t=<optimized out>, 
    __f=<optimized out>) at /usr/local/include/c++/7.3.0/bits/invoke.h:73
No locals.
#20 __invoke<void (folly::ThreadPoolExecutor::*&)(std::shared_ptr<folly::ThreadPoolExecutor::Thread>), folly::ThreadPoolExecutor*&, std::shared_ptr<folly::ThreadPoolExecutor::Thread>&> (__fn=<optimized out>)
    at /usr/local/include/c++/7.3.0/bits/invoke.h:95
No locals.
#21 __call<void, 0, 1> (__args=<optimized out>, this=<optimized out>) at /usr/local/include/c++/7.3.0/functional:467
No locals.
#22 operator()<> (this=<optimized out>) at /usr/local/include/c++/7.3.0/functional:551
No locals.
#23 folly::detail::function::FunctionTraits<void ()>::callBig<std::_Bind<void (folly::ThreadPoolExecutor::*(folly::ThreadPoolExecutor*, std::shared_ptr<folly::ThreadPoolExecutor::Thread>))(std::shared_ptr<folly::ThreadPoolExecutor::Thread>)> >(folly::detail::function::Data&) (p=...) at /home/couchbase/jenkins/cbdeps-ws/deps/packages/build/folly/folly-prefix/src/folly/folly/Function.h:401
        fn = <optimized out>
#24 0x0000000000ad1a84 in operator() (this=0x7f87d84a1380) at /home/couchbase/jenkins/workspace/toy-unix-simple/kv_engine/executor/folly_executorpool.cc:49
        fn = @0x7f87d84a1380: <error reading variable>
#25 operator() (__closure=0x7f87d84a1380) at /home/couchbase/jenkins/workspace/toy-unix-simple/kv_engine/executor/folly_executorpool.cc:49
        threadNameOpt = {storage_ = {{emptyState = -96 '\240', value = {static npos = 18446744073709551615, _M_dataplus = {<std::allocator<char>> = {<__gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>}, 
                  _M_p = 0x7f877cfe76a0 "NonIoPool2"}, _M_string_length = 10, {_M_local_buf = "NonIoPool2\000\000\000\000\000", _M_allocated_capacity = 8029725099528449870}}}, hasValue = true}}
        func = <error reading variable func (Cannot access memory at address 0x7f87d84a1380)>
#26 folly::detail::function::FunctionTraits<void ()>::callBig<CBRegisteredThreadFactory::newThread(folly::Function<void ()>&&)::{lambda()#1}>(folly::detail::function::Data&) (p=...)
    at /home/couchbase/jenkins/workspace/toy-unix-simple/server_build/tlm/deps/folly.exploded/include/folly/Function.h:401
        fn = @0x7f87d84a1380: <error reading variable>
#27 0x00007f87da70cd40 in execute_native_thread_routine () at /tmp/deploy/objdir/../gcc-10.2.0/libstdc++-v3/src/c++11/thread.cc:80
No locals.
#28 0x00007f87dc50ddd5 in start_thread (arg=0x7f877cff9700) at pthread_create.c:307
        __res = <optimized out>
        pd = 0x7f877cff9700
        now = <optimized out>
        unwind_buf = {cancel_jmp_buf = {{jmp_buf = {140219894437632, -5769999781670697130, 0, 8392704, 0, 140219894437632, 5828271686313559894, 5828624823543514966}, mask_was_saved = 0}}, priv = {pad = {0x0, 0x0, 0x0, 0x0}, data = {prev = 0x0, 
              cleanup = 0x0, canceltype = 0}}}
---Type <return> to continue, or q <return> to quit---
        not_first_call = <optimized out>
        pagesize_m1 = <optimized out>
        sp = <optimized out>
        freesize = <optimized out>
#29 0x00007f87d9e55ead in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111
No locals.
(gdb)