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https://issues.apache.org/jira/browse/ARROW-464?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15809567#comment-15809567
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Uwe L. Korn commented on ARROW-464:
-----------------------------------
I implemented those suggested changes locally and did notice a performance drop
of 20% as more reallocations still come in quite expensive, even with in-place
resizing provided by {{jemalloc}}. Also the overhead of calling {{nallocx}} is
in our case larger then we actually save by fully using the allocated space
(wastage is always <4KiB). Thus the above mentioned optimizations still sound
good theroretically to me but don't seem to bring a practical benefit.
Closing this as it is not a pressing issue. We can tackle this once someone has
a usecase.
> C++: More intelligent array growing
> -----------------------------------
>
> Key: ARROW-464
> URL: https://issues.apache.org/jira/browse/ARROW-464
> Project: Apache Arrow
> Issue Type: Improvement
> Components: C++
> Reporter: Uwe L. Korn
> Assignee: Uwe L. Korn
>
> Three things to consider:
> * Instead of always growing the memory to twice the size in the Builders, we
> should consider 1.5 as a growth factor as this still leads to less memory
> wastage. As the allocation costly is mostly linear in the number of newly
> requested pages, this shouldn't be a noticeable impact. Due to memory below
> the size of a single page (i.e. 4KiB) not being able to be expanded in place,
> we should keep the factor of there.
> * In the case of jemalloc, we can ask the allocator with the function
> {{nallocx}} for the size it would actually allocate for the requested size
> and then allocate this as the new capacity for the Builder/Buffer/... and not
> trigger an reallocation as long as the output of {{nallocx}} doesn't change.
> * If not using {{jemalloc}}, we should be careful about the cost of minor
> allocation size changes. It would be preferable in these cases to have also
> an implementation along the lines of {{nallocx}} that does some rounding to
> avoid unnecessary reallocations.
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