pitrou commented on code in PR #36622:
URL: https://github.com/apache/arrow/pull/36622#discussion_r1262505508
##########
docs/source/cpp/env_vars.rst:
##########
@@ -26,6 +26,28 @@ Arrow C++ at runtime. Many of these variables are inspected
only once per
process (for example, when the Arrow C++ DLL is loaded), so you cannot assume
that changing their value later will have an effect.
+.. envvar:: ACERO_ALIGNMENT_HANDLING
+
+ Arrow C++'s Acero module performs computation on streams of data. This
+ computation may involve a form of "type punning" that is technically
+ undefined behavior if the underlying array is not properly aligned. On
+ most modern CPUs this is not an issue, but some older CPUs may crash or
+ suffer poor performance. For this reason it is recommended that all
+ incoming array buffers are properly aligned.
+
+ The value of this environment variable controls what will happen when
+ Acero detects an unaligned buffer.
Review Comment:
```suggestion
Acero detects an unaligned buffer:
```
##########
docs/source/cpp/env_vars.rst:
##########
@@ -26,6 +26,28 @@ Arrow C++ at runtime. Many of these variables are inspected
only once per
process (for example, when the Arrow C++ DLL is loaded), so you cannot assume
that changing their value later will have an effect.
+.. envvar:: ACERO_ALIGNMENT_HANDLING
+
+ Arrow C++'s Acero module performs computation on streams of data. This
+ computation may involve a form of "type punning" that is technically
+ undefined behavior if the underlying array is not properly aligned. On
+ most modern CPUs this is not an issue, but some older CPUs may crash or
+ suffer poor performance. For this reason it is recommended that all
+ incoming array buffers are properly aligned.
+
+ The value of this environment variable controls what will happen when
+ Acero detects an unaligned buffer.
+
+ - ``warn`` a warning is emitted
+ - ``ignore`` nothing, alignment checking is disabled
+ - ``reallocate`` the buffer is reallocated to a properly aligned address
+ - ``error`` the operation will fail with an error
Review Comment:
```suggestion
- ``warn``: a warning is emitted
- ``ignore``: nothing, alignment checking is disabled
- ``reallocate``: the buffer is reallocated to a properly aligned address
- ``error``: the operation fails with an error
```
##########
docs/source/cpp/env_vars.rst:
##########
@@ -26,6 +26,28 @@ Arrow C++ at runtime. Many of these variables are inspected
only once per
process (for example, when the Arrow C++ DLL is loaded), so you cannot assume
that changing their value later will have an effect.
+.. envvar:: ACERO_ALIGNMENT_HANDLING
+
+ Arrow C++'s Acero module performs computation on streams of data. This
+ computation may involve a form of "type punning" that is technically
+ undefined behavior if the underlying array is not properly aligned. On
+ most modern CPUs this is not an issue, but some older CPUs may crash or
+ suffer poor performance. For this reason it is recommended that all
+ incoming array buffers are properly aligned.
Review Comment:
```suggestion
suffer poor performance. For this reason it is recommended that all
incoming array buffers are properly aligned, but some data sources
such as :ref:`Flight <flight-rpc>` may produce unaligned buffers.
```
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