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Posted to github@arrow.apache.org by "timwaizenegger (via GitHub)" <gi...@apache.org> on 2025/05/30 13:44:13 UTC
[PR] LocalFileSystem: let WalkDir return sorted results [arrow-rs-object-store]
timwaizenegger opened a new pull request, #389:
URL: https://github.com/apache/arrow-rs-object-store/pull/389
addresses https://github.com/apache/arrow-rs-object-store/issues/388
# Which issue does this PR close?
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Closes https://github.com/apache/arrow-rs-object-store/issues/388
# Rationale for this change
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offset listing is only usable if the list results are sorted. Only then can I use a member of the results I already have, to make another call that continues my listing.
# What changes are included in this PR?
Adds `sort_by_file_name()` call to `WalkDir` in `list_with_maybe_offset`. As far as I can tell, this is the only change needed to make local file offset listing possible.
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# Are there any user-facing changes?
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Re: [PR] LocalFileSystem: let WalkDir return sorted results [arrow-rs-object-store]
Posted by "tustvold (via GitHub)" <gi...@apache.org>.
tustvold commented on PR #389:
URL: https://github.com/apache/arrow-rs-object-store/pull/389#issuecomment-2922830949
list_with_offset is designed for listing everything after a given prefix, this is useful for data lake changelogs among other use-cases where you know you aren't interested in records before some time. I appreciate this isn't sufficient to add pagination, but that doesn't make it useless😅
If you need an ordered output, you will need to fetcy everything and sort, which is ultimately what this PR is proposing always doing and I am pushing back on.
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Re: [PR] LocalFileSystem: let WalkDir return sorted results [arrow-rs-object-store]
Posted by "tustvold (via GitHub)" <gi...@apache.org>.
tustvold commented on PR #389:
URL: https://github.com/apache/arrow-rs-object-store/pull/389#issuecomment-2922483966
Unfortunately this is a limitation that we can't reliably workaround, some stores such as S3 Express don't return data in sorted order, others don't support it at all. Ultimately list_with_offset is an optimisation for when you want everything after a given prefix.
FWIW #371 adds a way to do pagination, although it intentionally doesn't support filesystems.
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Re: [PR] LocalFileSystem: let WalkDir return sorted results [arrow-rs-object-store]
Posted by "tustvold (via GitHub)" <gi...@apache.org>.
tustvold commented on code in PR #389:
URL: https://github.com/apache/arrow-rs-object-store/pull/389#discussion_r2115996113
##########
src/local.rs:
##########
@@ -641,6 +641,7 @@ impl LocalFileSystem {
let walkdir = WalkDir::new(root_path)
// Don't include the root directory itself
.min_depth(1)
+ .sort_by_file_name()
Review Comment:
This will list every file in the directory, sort it, and then return it - at the very least this should be explicitly opt-in as directories can get very large - the standard library APIs are intentionally lazy
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Re: [PR] LocalFileSystem: let WalkDir return sorted results [arrow-rs-object-store]
Posted by "timwaizenegger (via GitHub)" <gi...@apache.org>.
timwaizenegger commented on code in PR #389:
URL: https://github.com/apache/arrow-rs-object-store/pull/389#discussion_r2116042705
##########
src/local.rs:
##########
@@ -641,6 +641,7 @@ impl LocalFileSystem {
let walkdir = WalkDir::new(root_path)
// Don't include the root directory itself
.min_depth(1)
+ .sort_by_file_name()
Review Comment:
That's true and you don't always need it. But sometimes you absolutely do; offset listing just makes no sense without sorting.
- offset listing: need sorting
- iterator listing: don't care about sorting, higher perf. without sorting
opt-out could be a good option too given those requirements
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Re: [PR] LocalFileSystem: let WalkDir return sorted results [arrow-rs-object-store]
Posted by "timwaizenegger (via GitHub)" <gi...@apache.org>.
timwaizenegger closed pull request #389: LocalFileSystem: let WalkDir return sorted results
URL: https://github.com/apache/arrow-rs-object-store/pull/389
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