Hattonuri opened a new pull request, #39397:
URL: https://github.com/apache/arrow/pull/39397
<!--
Thanks for opening a pull request!
If this is your first pull request you can find detailed information on how
to contribute here:
* [New Contributor's
Guide](https://arrow.apache.org/docs/dev/developers/guide/step_by_step/pr_lifecycle.html#reviews-and-merge-of-the-pull-request)
* [Contributing
Overview](https://arrow.apache.org/docs/dev/developers/overview.html)
If this is not a [minor
PR](https://github.com/apache/arrow/blob/main/CONTRIBUTING.md#Minor-Fixes).
Could you open an issue for this pull request on GitHub?
https://github.com/apache/arrow/issues/new/choose
Opening GitHub issues ahead of time contributes to the
[Openness](http://theapacheway.com/open/#:~:text=Openness%20allows%20new%20users%20the,must%20happen%20in%20the%20open.)
of the Apache Arrow project.
Then could you also rename the pull request title in the following format?
GH-${GITHUB_ISSUE_ID}: [${COMPONENT}] ${SUMMARY}
or
MINOR: [${COMPONENT}] ${SUMMARY}
In the case of PARQUET issues on JIRA the title also supports:
PARQUET-${JIRA_ISSUE_ID}: [${COMPONENT}] ${SUMMARY}
-->
### Rationale for this change
<!--
Why are you proposing this change? If this is already explained clearly in
the issue then this section is not needed.
Explaining clearly why changes are proposed helps reviewers understand your
changes and offer better suggestions for fixes.
-->
I've found that for-loop here
https://github.com/apache/arrow/blob/7c3480e2f028f5881242f227f42155cf833efee7/cpp/src/parquet/column_reader.cc#L1055-L1073
transforms into
`
0xc0c2f0 <ReadLevels()+96> inc %rdx
0xc0c2f3 <ReadLevels()+99> cmp %rax,%rdx
0xc0c2f6
<ReadLevels()+102> jge 0xc0c30c <ReadLevels()+124>
0xc0c2f8 <ReadLevels()+104> cmp %cx,(%r14,%rdx,2)
0xc0c2fd <ReadLevels()+109> jne 0xc0c2f0 <ReadLevels()+96>
0xc0c2ff <ReadLevels()+111> incq 0x0(%rbp)
0xc0c303 <ReadLevels()+115> mov (%rbx),%rax
0xc0c306 <ReadLevels()+118> jmp 0xc0c2f0 <ReadLevels()+96>
`
That means that it uses iteration element by element and moves
values_to_read counter every time using mov
I think that the reason is that values_to_read and num_def_levels are not
set as restrict. So the compiler can not optimize this to a more efficient
way(for example using simd)
On my flamegraph this part showed ~4% of time spent
In this file there also some for loops which could easily be changed to
std::count, but they do not touch references and I don't know the reason why
std::count was not used in the all cpp/src/parquet/ directory - so I didn't
change much
### What changes are included in this PR?
<!--
There is no need to duplicate the description in the issue here but it is
sometimes worth providing a summary of the individual changes in this PR.
-->
### Are these changes tested?
<!--
We typically require tests for all PRs in order to:
1. Prevent the code from being accidentally broken by subsequent changes
2. Serve as another way to document the expected behavior of the code
If tests are not included in your PR, please explain why (for example, are
they covered by existing tests)?
-->
### Are there any user-facing changes?
<!--
If there are user-facing changes then we may require documentation to be
updated before approving the PR.
-->
<!--
If there are any breaking changes to public APIs, please uncomment the line
below and explain which changes are breaking.
-->
<!-- **This PR includes breaking changes to public APIs.** -->
<!--
Please uncomment the line below (and provide explanation) if the changes fix
either (a) a security vulnerability, (b) a bug that caused incorrect or invalid
data to be produced, or (c) a bug that causes a crash (even when the API
contract is upheld). We use this to highlight fixes to issues that may affect
users without their knowledge. For this reason, fixing bugs that cause errors
don't count, since those are usually obvious.
-->
<!-- **This PR contains a "Critical Fix".** -->
--
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
To unsubscribe, e-mail: [email protected]
For queries about this service, please contact Infrastructure at:
[email protected]
