@Wes McKinney, Thanks a lot for the brainstorming. I think your ideas are reasonable and feasible. About IPC, my idea is that we can send the vector as a PointerStringVector, and receive it as a VarCharVector, so that the overhead of memory compaction can be hidden. What do you think?
Best, Liya Fan On Fri, Jul 12, 2019 at 11:07 AM Fan Liya <liya.fa...@gmail.com> wrote: > @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 >> > > > > >> > > > >> > > >> >
