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Re: [JAVA] Supporting zero copy arrow-vector


I opened a jira to describe what I think needs to be done here. Check it
out:

https://issues.apache.org/jira/browse/ARROW-3191


On Fri, Sep 7, 2018 at 10:47 AM Wes McKinney <wesmckinn@xxxxxxxxx> wrote:

> Seems like you should be able to construct an UnsafeDirectByteBuf from
> a MappedByteBuffer, and then wrap that with UnsafeDirectLittleEndian
> to get zero-copy access to a memory map. Does that sound right?
>
>
> https://github.com/netty/netty/blob/4.1/buffer/src/main/java/io/netty/buffer/UnpooledUnsafeDirectByteBuf.java
> On Fri, Sep 7, 2018 at 12:46 PM Zhenyuan Zhao <zzymtn@xxxxxxxxx> wrote:
> >
> > Interesting, so basically I can still use the public constructor
> >
> > public ArrowBuf(AtomicInteger refCnt, BufferLedger ledger,
> > UnsafeDirectLittleEndian byteBuf, BufferManager manager,
> > ArrowByteBufAllocator alloc, int offset, int length, boolean isEmpty)
> >
> > Instead, override BufferLedger/UnsafeDirectLittleEndian/BufferManager to
> > make it reference existing buffer. That is a much more plausible option
> as
> > it will reuse the Vectors. All I need is to implement my own
> deserializer.
> > Did I get you right?
> >
> > Thanks
> >
> > On Fri, Sep 7, 2018 at 7:09 AM Jacques Nadeau <jacques@xxxxxxxxxx>
> wrote:
> >
> > > It is on purpose that the ArrowBuf is final. It is done to ensure a
> single
> > > impl and performance reasons. ArrowBuf is primarily a memory address
> and a
> > > length and wants zero indirection to the reading/writing of that.
> > >
> > > It does, however, wrap several types of substructures as long as they
> have
> > > that property. For example, an ArrowBuf almost always currently wraps a
> > > Netty UnsafeDirectLittleEndian object. At that level you could propose
> a
> > > way to wrap more types of memory addresses+lengths.
> > >
> > > On Thu, Sep 6, 2018, 10:26 PM Zhenyuan Zhao <zzymtn@xxxxxxxxx> wrote:
> > >
> > > > Hello Team,
> > > >
> > > > I'm working on using arrow as intermediate format for transferring
> > > columnar
> > > > data from server to client. In this case, the client will only need
> to
> > > read
> > > > from the format so I would like to avoid any unnecessary copy of the
> > > data.
> > > > Looking into arrow, while arrow-format/flatbuffers does support zero
> > > copy,
> > > > current arrow-vector java implementation is not. I was trying to hack
> > > zero
> > > > copy for readonly scenarios, but saw two main blockers:
> > > >
> > > >    1.
> > > >
> > > >    ArrowBuf is the only buffer implementation used exclusively across
> > > >    ArrowReader/ArrowRecordBatch/Vectors. It's final, which means
> there
> > > > isn't a
> > > >    way for me to override its logic in order to wrap some existing
> > > buffer.
> > > >    It's absolutely necessary to use ArrowBuf for write scenarios due
> to
> > > > buffer
> > > >    allocation, but for read, I was hoping vector can just serve as
> view
> > > on
> > > > top
> > > >    of existing memory buffer (like java ByteBuffer or netty ByteBuf).
> > > Seems
> > > >    safe for read only case.
> > > >    2.
> > > >
> > > >    As a result of #1 <https://github.com/apache/arrow/pull/1>
> described
> > > >    above, the only layer which seems reusable is the arrow-format.
> Then I
> > > > have
> > > >    to implement effectively a readonly copy of arrow-vector that
> > > references
> > > >    existing buffer. Put aside the effort doing that, it introduces a
> big
> > > > gap
> > > >    to keep up with future changes/fixes made to arrow-vector.
> > > >
> > > > Wondering if you guys have put any thoughts into such readonly
> scenarios.
> > > > Any suggestion how I can approach this myself?
> > > >
> > > > Thanks
> > > >
> > >
>