Occasional seg fault

Hi there. I'm facing a seg fault problem that happens occasionally. I wonder if you have any suggestion about how I can debug and locate the root cause. Below is an example of the stack trace. Any ideas welcome. Thanks in advance.

```
signal (11): Segmentation fault
in expression starting at /myapp/scripts/start_service.jl:8
unknown function (ip: 0x7f44fae4ee63)
pydecref_ at /myapp/.julia/packages/PyCall/zqDXB/src/PyCall.jl:114
pydecref at /myapp/.julia/packages/PyCall/zqDXB/src/PyCall.jl:119
_jl_invoke at /buildworker/worker/package_linux64/build/src/gf.c:2135 [inlined]
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2305
jl_apply at /buildworker/worker/package_linux64/build/src/julia.h:1631 [inlined]
run_finalizer at /buildworker/worker/package_linux64/build/src/gc.c:231
jl_gc_run_finalizers_in_list at /buildworker/worker/package_linux64/build/src/gc.c:317
jl_gc_collect at /buildworker/worker/package_linux64/build/src/gc.c:345
maybe_collect at /buildworker/worker/package_linux64/build/src/gc.c:781 [inlined]
jl_gc_counted_realloc_with_old_size at /buildworker/worker/package_linux64/build/src/gc.c:3051
__gmpz_realloc at /usr/local/julia/bin/../lib/julia/libgmp.so (unknown line)
__gmpz_set_str at /usr/local/julia/bin/../lib/julia/libgmp.so (unknown line)
__gmp_doscan at /usr/local/julia/bin/../lib/julia/libgmp.so (unknown line)
__gmp_sscanf at /usr/local/julia/bin/../lib/julia/libgmp.so (unknown line)
ffi_call_unix64 at /usr/local/lib/python3.7/dist-packages/.libs_cffi_backend/libffi-806b1a9d.so.6.0.4 (unknown line)
ffi_call at /usr/local/lib/python3.7/dist-packages/.libs_cffi_backend/libffi-806b1a9d.so.6.0.4 (unknown line)
cdata_call at /tmp/pip-req-build-nthnqcsy/c/_cffi_backend.c:3130
_PyObject_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
unknown function (ip: 0x7f44facad4d2)
_PyFunction_FastCallDict at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyObject_Call_Prepend at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
unknown function (ip: 0x7f44fae49af4)
unknown function (ip: 0x7f44fae53071)
_PyObject_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
unknown function (ip: 0x7f44facad4d2)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
unknown function (ip: 0x7f44facad4d2)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
unknown function (ip: 0x7f44facad4d2)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
unknown function (ip: 0x7f44facad4d2)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallDict at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyObject_Call_Prepend at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
PyObject_Call at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallDict at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyObject_Call_Prepend at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
PyObject_Call at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallDict at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyObject_Call_Prepend at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
PyObject_Call at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallDict at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyObject_Call_Prepend at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
PyObject_Call at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
unknown function (ip: 0x7f44facad4d2)
_PyFunction_FastCallDict at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
unknown function (ip: 0x7f44fae4996c)
unknown function (ip: 0x7f44fad7f6c0)
_PyObject_GC_Malloc at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyObject_GC_New at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
unknown function (ip: 0x7f44fae698ee)
PyObject_GetIter at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
unknown function (ip: 0x7f44facad4d2)
_PyFunction_FastCallDict at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
unknown function (ip: 0x7f44fae4b588)
PyObject_GetIter at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
unknown function (ip: 0x7f44fae9919f)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
unknown function (ip: 0x7f44facad4d2)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
unknown function (ip: 0x7f44facad4d2)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallDict at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyObject_Call_Prepend at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
PyObject_Call at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallDict at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyObject_Call_Prepend at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
PyObject_Call at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallKeywords at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalFrameDefault at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyEval_EvalCodeWithName at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyFunction_FastCallDict at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
_PyObject_Call_Prepend at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
PyObject_Call at /usr/lib/x86_64-linux-gnu/libpython3.7m.so.1.0 (unknown line)
macro expansion at /myapp/.julia/packages/PyCall/zqDXB/src/exception.jl:93 [inlined]
#110 at /myapp/.julia/packages/PyCall/zqDXB/src/pyfncall.jl:43 [inlined]
disable_sigint at ./c.jl:446 [inlined]
__pycall! at /myapp/.julia/packages/PyCall/zqDXB/src/pyfncall.jl:42 [inlined]
_pycall! at /myapp/.julia/packages/PyCall/zqDXB/src/pyfncall.jl:29
#_#117 at /myapp/.julia/packages/PyCall/zqDXB/src/pyfncall.jl:11 [inlined]
PyObject at /myapp/.julia/packages/PyCall/zqDXB/src/pyfncall.jl:86
_jl_invoke at /buildworker/worker/package_linux64/build/src/gf.c:2135 [inlined]
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2305
get_SF_cols at /myapp/src/sf_copy.jl:134
sf_copy_table at /myapp/src/sf_copy.jl:40
macro expansion at ./util.jl:212 [inlined]
#52 at /myapp/src/sf_copy.jl:5
iterate at ./generator.jl:47 [inlined]
collect_to! at ./array.jl:667 [inlined]
collect_to_with_first! at ./array.jl:646
_collect at ./array.jl:640
map at ./array.jl:564 [inlined]
sf_copy_tables at /myapp/src/sf_copy.jl:4
macro expansion at ./util.jl:212 [inlined]
process_pb_upload at /myapp/src/process_pb.jl:77
macro expansion at /myapp/src/process_pb.jl:25 [inlined]
handle_pb_upload_request at /myapp/.julia/packages/ContextTracker/7ckyU/src/trace.jl:38
macro expansion at ./util.jl:212 [inlined]
macro expansion at /myapp/src/main.jl:33 [inlined]
process_request at /myapp/.julia/packages/ContextTracker/7ckyU/src/trace.jl:38
unknown function (ip: 0x7f44e91f40bf)
_jl_invoke at /buildworker/worker/package_linux64/build/src/gf.c:2135 [inlined]
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2305
macro expansion at /myapp/src/main.jl:14 [inlined]
start_sqs_processing at /myapp/.julia/packages/ContextTracker/7ckyU/src/trace.jl:38
unknown function (ip: 0x7f451c23df6c)
_jl_invoke at /buildworker/worker/package_linux64/build/src/gf.c:2141 [inlined]
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2305
jl_apply at /buildworker/worker/package_linux64/build/src/julia.h:1631 [inlined]
do_call at /buildworker/worker/package_linux64/build/src/interpreter.c:328
eval_value at /buildworker/worker/package_linux64/build/src/interpreter.c:417
eval_body at /buildworker/worker/package_linux64/build/src/interpreter.c:641
eval_body at /buildworker/worker/package_linux64/build/src/interpreter.c:705
eval_body at /buildworker/worker/package_linux64/build/src/interpreter.c:705
jl_interpret_toplevel_thunk_callback at /buildworker/worker/package_linux64/build/src/interpreter.c:888
unknown function (ip: 0xfffffffffffffffe)
unknown function (ip: 0x7f451edbd90f)
unknown function (ip: 0xb)
jl_interpret_toplevel_thunk at /buildworker/worker/package_linux64/build/src/interpreter.c:897
jl_toplevel_eval_flex at /buildworker/worker/package_linux64/build/src/toplevel.c:814
jl_parse_eval_all at /buildworker/worker/package_linux64/build/src/ast.c:873
jl_load at /buildworker/worker/package_linux64/build/src/toplevel.c:878
include at ./boot.jl:328 [inlined]
include_relative at ./loading.jl:1105
include at ./Base.jl:31
_jl_invoke at /buildworker/worker/package_linux64/build/src/gf.c:2135 [inlined]
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2305
exec_options at ./client.jl:287
_start at ./client.jl:460
jfptr__start_2084.clone_1 at /usr/local/julia/lib/julia/sys.so (unknown line)
_jl_invoke at /buildworker/worker/package_linux64/build/src/gf.c:2135 [inlined]
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2305
unknown function (ip: 0x401931)
unknown function (ip: 0x401533)
__libc_start_main at /lib/x86_64-linux-gnu/libc.so.6 (unknown line)
unknown function (ip: 0x4015d4)
Allocations: 2338671402 (Pool: 2337259964; Big: 1411438); GC: 3050
```