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From "Uwe L. Korn (JIRA)" <>
Subject [jira] [Closed] (ARROW-464) C++: More intelligent array growing
Date Sun, 08 Jan 2017 15:36:58 GMT


Uwe L. Korn closed ARROW-464.
    Resolution: Won't Fix

> C++: More intelligent array growing
> -----------------------------------
>                 Key: ARROW-464
>                 URL:
>             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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