Tim Armstrong created IMPALA-9399:
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Summary: Optimise RuntimeProfile::ToThrift()
Key: IMPALA-9399
URL: https://issues.apache.org/jira/browse/IMPALA-9399
Project: IMPALA
Issue Type: Sub-task
Components: Backend
Reporter: Tim Armstrong
I looked at the RuntimeProfile::ToThrift() part of the dop16 profile from the
parent JIRA -
https://issues.apache.org/jira/secure/attachment/12993392/coord_q5_dop16.svg.
There are some minor inefficiencies within ToThrift(), e.g. constructing
vectors then copying them immediately.
The majority of time, though, is spent in TRuntimeProfileNode() and
~TRuntimeProfileNode(). The only place those would be invoked from ToThrift()
is in this line at
https://github.com/apache/impala/blob/f2f348c0f93208a0f34c33b6a4dc82f4d9d4b290/be/src/util/runtime-profile.cc#L1174:
{code}
nodes->push_back(TRuntimeProfileNode());
{code}
I scratched my head and started at our code a bit, then went and looked at the
std::vector and thrift-generated code. I believe this line in std::vector is
the problem
https://github.com/gcc-mirror/gcc/blob/releases/gcc-4.9.2/libstdc%2B%2B-v3/include/bits/vector.tcc#L421
{code}
__new_finish
= std::__uninitialized_move_if_noexcept_a
(this->_M_impl._M_start, this->_M_impl._M_finish,
__new_start, _M_get_Tp_allocator());
{code}
It can't use the move constructor of the TRuntimeProfileNode, because of some
c++ exception-safety guarantees and the fact that the constructor is not marked
noexcept. I don't think there's an easy way to avoid this without changing the
code generated by thrift.
I played around with the compiler explorer and it looks like it generates much
better code with the noexcept added: https://godbolt.org/z/ZTSMHY
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