libutil/tarfile: Create the scratch std::vector only once (backport #13175)#13577
Merged
mergify[bot] merged 1 commit into2.28-maintenancefrom Jul 30, 2025
Merged
Conversation
I can't find a good way to benchmark in isolation from the git cache, but common sense dictates that creating (and destroying) a 131KiB std::vector for each regular file from the archive imposes quite a significant overhead regardless of the IO bound git cache. AFAICT there is no reason to keep a copy of the data since it always gets fed into the sink and there are no coroutines/threads in sight. (cherry picked from commit 7628155)
mergify
bot
added
automatic backport
mergify
bot
added
merge-queue
automatic backport
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Motivation
AFAICT there is no reason to keep a copy of the data since it always gets fed into the sink and there are no coroutines/threads in sight.
I can't find a good way to benchmark in isolation from the git cache, but common sense dictates that creating (and destroying) a 131KiB
std::vectorfor each 131KiB chunk of a regular file from the archive imposes quite a significant overhead regardless of the IO bound git cache.cc @edolstra git blame points me to #9485 for when this was first introduced. Since then code was moved quite a bit by @Ericson2314. Is there some reason this was done this way and stuff just got lost during refactorings?
Context
Should help a bit with #10683
Add 👍 to pull requests you find important.
The Nix maintainer team uses a GitHub project board to schedule and track reviews.
This is an automatic backport of pull request #13175 done by [Mergify](https://mergify.com).