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https://issues.apache.org/jira/browse/IMPALA-9399?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Work on IMPALA-9399 started by Tim Armstrong.
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> 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
> Assignee: Tim Armstrong
> Priority: Major
> Labels: perf
>
> 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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