@Uwe L. Korn Thanks a lot for the suggestion. I think this is exactly what we are doing right now.
Best, Liya Fan On Thu, Jul 11, 2019 at 9:44 PM Wes McKinney <wesmck...@gmail.com> wrote: > 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 > > > > > > > > > > > > >
