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Posted to github@arrow.apache.org by GitBox <gi...@apache.org> on 2021/12/22 12:04:26 UTC
[GitHub] [arrow] alamb opened a new pull request #12019: (docs) Clarify that offsets are monotonic for binary like arrays
alamb opened a new pull request #12019:
URL: https://github.com/apache/arrow/pull/12019
# Rationale
The question of "what are the values of the offsets for non-valid entries in arrays" came up in arrow-rs: https://github.com/apache/arrow-rs/issues/1071 and the existing [docs](https://arrow.apache.org/docs/format/Columnar.html#variable-size-binary-layout) seem to be somewhat vague on this issue.
I looked at three implementations of arrow, and they all seem to assume / validate the offsets are monotonic:
* C++ implementation (I think) also also ensures the offsets are monotonic without first checking the validity array https://github.com/apache/arrow/blob/master/cpp/src/arrow/array/validate.cc#L568-L592
* arrow-rs after https://github.com/apache/arrow-rs/pull/921 (based on the C++) will refuse to create arrays where the array offsets are non monotonic
* arrow2 also ensures that offsets are always monotonic.
https://github.com/jorgecarleitao/arrow2/blob/37a9c758826a92d98dc91e992b2a49ce9724095d/src/array/specification.rs#L102-L119
# Changes
Thus I propose updating the format docs to make the monotonic offsets explicit.
# Background
I think @jorgecarleitao's description on https://github.com/apache/arrow-rs/issues/1071#issuecomment-998481607, explains the reason why having monotonic offsets is a good idea
> I think that in general the property we seek is: discarding the validity cannot result in UB when accessing the values. This justifies the values buffer of a primitive array is always initialized, and the offsets being valid and in-bounds even in null cases.
>
> The rational for this is that sometimes it is faster to skip validity accesses and only iterate over the values (and clone the validity). I do not recall the benchmark result, but this may explain why string comparison ignores validity and & the bitmaps instead.
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[GitHub] [arrow] pitrou closed pull request #12019: ARROW-15244: [Format] Clarify that offsets are monotonic for binary like arrays
Posted by GitBox <gi...@apache.org>.
pitrou closed pull request #12019:
URL: https://github.com/apache/arrow/pull/12019
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[GitHub] [arrow] ursabot edited a comment on pull request #12019: ARROW-15244: [Format] Clarify that offsets are monotonic for binary like arrays
Posted by GitBox <gi...@apache.org>.
ursabot edited a comment on pull request #12019:
URL: https://github.com/apache/arrow/pull/12019#issuecomment-1005379380
Benchmark runs are scheduled for baseline = 31a07be1d9dc2f7c9720cc0fdcd7f083d947aba1 and contender = e7dc8f573773d2463be997236ceef7bffd6d00c5. e7dc8f573773d2463be997236ceef7bffd6d00c5 is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Finished :arrow_down:0.0% :arrow_up:0.0%] [ec2-t3-xlarge-us-east-2](https://conbench.ursa.dev/compare/runs/267baedc3d9d41f3a3a3ef263ff9187e...fa6313c2943242f8a17722b6335d1a2e/)
[Scheduled] [ursa-i9-9960x](https://conbench.ursa.dev/compare/runs/12b49a67ff1d4420aab5273b8e68eb09...3d4d8fe5d7e54776803dd9221e28bfa5/)
[Scheduled] [ursa-thinkcentre-m75q](https://conbench.ursa.dev/compare/runs/14aa1ce144a84dc392d264fa451596e6...23a409850370402b8bef02e5e248c39c/)
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python. Runs only benchmarks with cloud = True
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java
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[GitHub] [arrow] ursabot commented on pull request #12019: ARROW-15244: [Format] Clarify that offsets are monotonic for binary like arrays
Posted by GitBox <gi...@apache.org>.
ursabot commented on pull request #12019:
URL: https://github.com/apache/arrow/pull/12019#issuecomment-1005379380
Benchmark runs are scheduled for baseline = 31a07be1d9dc2f7c9720cc0fdcd7f083d947aba1 and contender = e7dc8f573773d2463be997236ceef7bffd6d00c5. e7dc8f573773d2463be997236ceef7bffd6d00c5 is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Scheduled] [ec2-t3-xlarge-us-east-2](https://conbench.ursa.dev/compare/runs/267baedc3d9d41f3a3a3ef263ff9187e...fa6313c2943242f8a17722b6335d1a2e/)
[Scheduled] [ursa-i9-9960x](https://conbench.ursa.dev/compare/runs/12b49a67ff1d4420aab5273b8e68eb09...3d4d8fe5d7e54776803dd9221e28bfa5/)
[Scheduled] [ursa-thinkcentre-m75q](https://conbench.ursa.dev/compare/runs/14aa1ce144a84dc392d264fa451596e6...23a409850370402b8bef02e5e248c39c/)
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python. Runs only benchmarks with cloud = True
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java
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[GitHub] [arrow] github-actions[bot] commented on pull request #12019: (docs) Clarify that offsets are monotonic for binary like arrays
Posted by GitBox <gi...@apache.org>.
github-actions[bot] commented on pull request #12019:
URL: https://github.com/apache/arrow/pull/12019#issuecomment-999526386
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[GitHub] [arrow] github-actions[bot] commented on pull request #12019: ARROW-15244: [Format] Clarify that offsets are monotonic for binary like arrays
Posted by GitBox <gi...@apache.org>.
github-actions[bot] commented on pull request #12019:
URL: https://github.com/apache/arrow/pull/12019#issuecomment-1004941015
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[GitHub] [arrow] jorgecarleitao commented on a change in pull request #12019: (docs) Clarify that offsets are monotonic for binary like arrays
Posted by GitBox <gi...@apache.org>.
jorgecarleitao commented on a change in pull request #12019:
URL: https://github.com/apache/arrow/pull/12019#discussion_r773843991
##########
File path: docs/source/format/Columnar.rst
##########
@@ -309,7 +309,11 @@ That is, a null value may occupy a **non-empty** memory space in the data
buffer. When this is true, the content of the corresponding memory space
is undefined.
-Generally the first value in the offsets array is 0, and the last slot
+Offsets must be monotonic, that is `offsets[j+1] >= offsets[j]` for
+`0 <= j < length`, even for null vaues. This property ensures the
Review comment:
```suggestion
`0 <= j < length`, even for null slots. This property ensures the
```
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[GitHub] [arrow] pitrou commented on a change in pull request #12019: (docs) Clarify that offsets are monotonic for binary like arrays
Posted by GitBox <gi...@apache.org>.
pitrou commented on a change in pull request #12019:
URL: https://github.com/apache/arrow/pull/12019#discussion_r778202893
##########
File path: docs/source/format/Columnar.rst
##########
@@ -309,7 +309,11 @@ That is, a null value may occupy a **non-empty** memory space in the data
buffer. When this is true, the content of the corresponding memory space
is undefined.
-Generally the first value in the offsets array is 0, and the last slot
+Offsets must be monotonically increasing, that is `offsets[j+1] >= offsets[j]` for
+`0 <= j < length`, even for null slots. This property ensures the
+**location** for all values is valid and well defined.
Review comment:
```suggestion
Offsets must be monotonically increasing, that is ``offsets[j+1] >= offsets[j]``
for ``0 <= j < length``, even for null slots. This property ensures the
location for all values is valid and well defined.
```
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[GitHub] [arrow] alamb commented on pull request #12019: (docs) Clarify that offsets are monotonic for binary like arrays
Posted by GitBox <gi...@apache.org>.
alamb commented on pull request #12019:
URL: https://github.com/apache/arrow/pull/12019#issuecomment-999531339
I also started a mailing list thread on this topic: https://lists.apache.org/thread/fx8k250nn1d9b86sfo9t2gcl1v11mn4f
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[GitHub] [arrow] ursabot edited a comment on pull request #12019: ARROW-15244: [Format] Clarify that offsets are monotonic for binary like arrays
Posted by GitBox <gi...@apache.org>.
ursabot edited a comment on pull request #12019:
URL: https://github.com/apache/arrow/pull/12019#issuecomment-1005379380
Benchmark runs are scheduled for baseline = 31a07be1d9dc2f7c9720cc0fdcd7f083d947aba1 and contender = e7dc8f573773d2463be997236ceef7bffd6d00c5. e7dc8f573773d2463be997236ceef7bffd6d00c5 is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Finished :arrow_down:0.0% :arrow_up:0.0%] [ec2-t3-xlarge-us-east-2](https://conbench.ursa.dev/compare/runs/267baedc3d9d41f3a3a3ef263ff9187e...fa6313c2943242f8a17722b6335d1a2e/)
[Failed :arrow_down:0.45% :arrow_up:0.0%] [ursa-i9-9960x](https://conbench.ursa.dev/compare/runs/12b49a67ff1d4420aab5273b8e68eb09...3d4d8fe5d7e54776803dd9221e28bfa5/)
[Failed :arrow_down:0.79% :arrow_up:0.0%] [ursa-thinkcentre-m75q](https://conbench.ursa.dev/compare/runs/14aa1ce144a84dc392d264fa451596e6...23a409850370402b8bef02e5e248c39c/)
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python. Runs only benchmarks with cloud = True
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java
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[GitHub] [arrow] jorgecarleitao commented on a change in pull request #12019: (docs) Clarify that offsets are monotonic for binary like arrays
Posted by GitBox <gi...@apache.org>.
jorgecarleitao commented on a change in pull request #12019:
URL: https://github.com/apache/arrow/pull/12019#discussion_r773843991
##########
File path: docs/source/format/Columnar.rst
##########
@@ -309,7 +309,11 @@ That is, a null value may occupy a **non-empty** memory space in the data
buffer. When this is true, the content of the corresponding memory space
is undefined.
-Generally the first value in the offsets array is 0, and the last slot
+Offsets must be monotonic, that is `offsets[j+1] >= offsets[j]` for
+`0 <= j < length`, even for null vaues. This property ensures the
Review comment:
```suggestion
`0 <= j < length`, even for null values. This property ensures the
```
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[GitHub] [arrow] mbrobbel commented on a change in pull request #12019: (docs) Clarify that offsets are monotonic for binary like arrays
Posted by GitBox <gi...@apache.org>.
mbrobbel commented on a change in pull request #12019:
URL: https://github.com/apache/arrow/pull/12019#discussion_r774470963
##########
File path: docs/source/format/Columnar.rst
##########
@@ -309,7 +309,11 @@ That is, a null value may occupy a **non-empty** memory space in the data
buffer. When this is true, the content of the corresponding memory space
is undefined.
-Generally the first value in the offsets array is 0, and the last slot
+Offsets must be monotonic, that is `offsets[j+1] >= offsets[j]` for
Review comment:
```suggestion
Offsets must be monotonically increasing, that is `offsets[j+1] >= offsets[j]` for
```
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[GitHub] [arrow] ursabot edited a comment on pull request #12019: ARROW-15244: [Format] Clarify that offsets are monotonic for binary like arrays
Posted by GitBox <gi...@apache.org>.
ursabot edited a comment on pull request #12019:
URL: https://github.com/apache/arrow/pull/12019#issuecomment-1005379380
Benchmark runs are scheduled for baseline = 31a07be1d9dc2f7c9720cc0fdcd7f083d947aba1 and contender = e7dc8f573773d2463be997236ceef7bffd6d00c5. e7dc8f573773d2463be997236ceef7bffd6d00c5 is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Finished :arrow_down:0.0% :arrow_up:0.0%] [ec2-t3-xlarge-us-east-2](https://conbench.ursa.dev/compare/runs/267baedc3d9d41f3a3a3ef263ff9187e...fa6313c2943242f8a17722b6335d1a2e/)
[Failed :arrow_down:0.45% :arrow_up:0.0%] [ursa-i9-9960x](https://conbench.ursa.dev/compare/runs/12b49a67ff1d4420aab5273b8e68eb09...3d4d8fe5d7e54776803dd9221e28bfa5/)
[Scheduled] [ursa-thinkcentre-m75q](https://conbench.ursa.dev/compare/runs/14aa1ce144a84dc392d264fa451596e6...23a409850370402b8bef02e5e248c39c/)
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python. Runs only benchmarks with cloud = True
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java
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