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From Chris Nuernberger <ch...@techascent.com>
Subject Re: Bulk copy methods to/from Java vectors
Date Sun, 26 Jul 2020 12:48:30 GMT
Perfect, thank you.  I tried setCapacity and setValueCount together and
this didn't have the result I was hoping for.  The methods you provide are
what I was looking for.

On Sat, Jul 25, 2020 at 5:22 PM Jacques Nadeau <jacques@apache.org> wrote:

> You can allocate exactly for both fixed [1] and variable types [2].
>
> 1:
> https://github.com/apache/arrow/blob/master/java/vector/src/main/java/org/apache/arrow/vector/BaseFixedWidthVector.java#L292
> 2:
> https://github.com/apache/arrow/blob/master/java/vector/src/main/java/org/apache/arrow/vector/BaseVariableWidthVector.java#L401
>
> You can then use the set method per cell or just grab the memory address
> (e.g. getDataBufferAddress()) and use Unsafe to bulk copy. The latter
> obviously is more advanced and requires you do things like set the
> validity buffers as well.
>
>
> On Sat, Jul 25, 2020 at 6:02 AM Chris Nuernberger <chris@techascent.com>
> wrote:
>
>> Hey,
>>
>> I would like to have bulk methods for copying data into a vector.
>> Specifically, I have an existing data table so I know the desired lengths
>> of the columns.  I can also precalculate the necessary buffer sizes for any
>> variable sized column.
>>
>>
>> What I don't see is how to pre-allocate columns of a given size.  When I
>> use setValueCount on a column and then use the set method I get a netty
>> error.  What I was hoping for is some allocation method, especially for
>> primitive data, that allocates the desired uninitialized memory for the
>> valide and buffer data and then hands those two buffers back to me so I can
>> use memcpy and friends as opposed to repeated calls to setSafe.
>>
>>
>> Repeated calls to setSafe are time consuming, not parallelizable, and
>> unnecessary when I know the data rectangle I would like to transfer into a
>> record batch.
>>
>>
>> In my case I have the data pre-cut.  How would you recommend copying bulk
>> portions of data (that may be in java arrays or in some more abstract
>> interface) into a record batch?
>>
>> Thanks for any help,
>>
>> Chris
>>
>

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