hi Liya -- have you thought about implementing this as an ExtensionType / ExtensionVector? You actually can already do this, so if this helps you reference strings stored in some external memory then that seems reasonable. Such a PointerStringVector could have a method that converts it into the Arrow varbinary columnar representation.
You wouldn't be able to put such an object into the IPC binary protocol, though. If that's a requirement (being able to use the IPC protocol) for this kind of data, before going any further in the discussion I would suggest that you work out exactly how such data would be moved from one process address space to another (using Buffers). - Wes On Thu, Jul 11, 2019 at 7:35 AM Uwe L. Korn <uw...@xhochy.com> wrote: > > Hello Liya Fan, > > here your best approach is to copy into the Arrow format as you can then use > this as the basis for working with the Arrow-native representation as well as > your internal representation. You will have to use two different offset > vector as those two will always differ but in the case of your internal > representation, you don't have the requirement of consecutive data as Arrow > has but you can still work with the strings just as before even when stored > consecutively. > > Uwe > > On Thu, Jul 11, 2019, at 2:24 PM, Fan Liya wrote: > > Hi Korn, > > > > Thanks a lot for your comments. > > > > In my opinion, your comments make sense to me. Allowing non-consecutive > > memory segments will break some good design choices of Arrow. > > However, there are wide-spread user requirements for non-consecutive memory > > segments. I am wondering how can we help such users. What advice we can > > give to them? > > > > Memory copy/move can be a solution, but is there a better solution? > > Is there a third alternative? Can we virtualize the non-consecutive memory > > segments into a consecutive one? (Although performance overhead is > > unavoidable.) > > > > What do you think? Let's brain-storm it. > > > > Best, > > Liya Fan > > > > > > On Thu, Jul 11, 2019 at 8:05 PM Uwe L. Korn <uw...@xhochy.com> wrote: > > > > > Hello Liya, > > > > > > I'm quite -1 on this type as Arrow is about efficient columnar structures. > > > We have opened the standard also to matrix-like types but always keep the > > > constraint of consecutive memory. Now also adding types where memory is no > > > longer consecutive but spread in the heap will make the scope of the > > > project much wider (It seems that we then just turn into a general > > > serialization framework). > > > > > > One of the ideas of a common standard is that some need to make > > > compromises. I think in this case it is a necessary compromise to not > > > allow > > > all kind of string representations. > > > > > > Uwe > > > > > > On Thu, Jul 11, 2019, at 6:01 AM, Fan Liya wrote: > > > > Hi all, > > > > > > > > > > > > We are thinking of providing varchar/varbinary vectors with a different > > > > memory layout which exists in a wide range of systems. The memory layout > > > is > > > > different from that of VarCharVector in the following ways: > > > > > > > > > > > > 1. > > > > > > > > Instead of storing (start offset, end offset), the new layout stores > > > > (start offset, length) > > > > 2. > > > > > > > > The content of varchars may not be in a consecutive memory region. > > > > Instead, it can be in arbitrary memory address. > > > > > > > > > > > > Due to these differences in memory layout, it incurs performance > > > > overhead > > > > when converting data between existing systems and VarCharVectors. > > > > > > > > The above difference 1 seems insignificant, while difference 2 is > > > difficult > > > > to overcome. However, the scenario of difference 2 is prevalent in > > > > practice: for example we store strings in a series of memory segments. > > > > Whenever a segment is full, we request a new one. However, these memory > > > > segments may not be consecutive, because other processes/threads are > > > > also > > > > requesting/releasing memory segments in the meantime. > > > > > > > > So we are wondering if it is possible to support such memory layout in > > > > Arrow. I think there are more systems that are trying to adopting Arrow, > > > > but are hindered by such difficulty. > > > > > > > > Would you please give your valuable feedback? > > > > > > > > > > > > Best, > > > > > > > > Liya Fan > > > > > > > > >
