[jira] [Resolved] (IMPALA-9399) Optimise RuntimeProfile::ToThrift()

["Tim Armstrong (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/IMPALA-9399?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Tim Armstrong resolved IMPALA-9399.
-----------------------------------
    Fix Version/s: Impala 3.4.0
       Resolution: Fixed

> 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
>             Fix For: Impala 3.4.0
>
>
> 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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