pyarrow at least treats the KeyValue values as binary and not UTF-8.
On Sun, Jul 11, 2021 at 9:40 PM Micah Kornfield <emkornfi...@gmail.com> wrote: > > I think other languages (e.g. java, python) might make more of distinction > between utf-8 compatible strings and raw bytes. For python it might be less > of a concern if the c++ wrapper already makes the value field look like a > bytes field > > On Sunday, July 11, 2021, Wes McKinney <wesmck...@gmail.com> wrote: >> >> We could certainly "upgrade" KeyValue to have a binary value field >> everywhere KeyValue is used, but there is some risk of code in the >> wild expecting there to be a null terminator after the string data. >> The Flatbuffers-generated accessor APIs do not depend on the existence >> of the null terminator, though. Not ideal, but I would not be thrilled >> about adding an extra [ BinaryKeyValue ] everyplace we currently have >> [ KeyValue ]. >> >> That said, I doubt that we have any endogenous forward compatibility >> problems related to this in Apache Arrow-maintained libraries, the >> risk would come from users who are interacting with the Flatbuffers >> data manually / without using one of our libraries. We could implement >> the changes and run a set of forward compatibility integration tests >> to see if anyone of our released libraries have an issue. >> >> On Fri, Jul 9, 2021 at 11:33 AM Wes McKinney <wesmck...@gmail.com> wrote: >> > >> > The cost of an empty vector in Flatbuffers appears to be 4 bytes. >> > >> > On Wed, Jul 7, 2021 at 5:50 PM Micah Kornfield <emkornfi...@gmail.com> >> > wrote: >> > > >> > > Retitling and forking the discussion to talk about key value pairs. >> > > >> > > What is the byte cost of an empty list? Another option would be to >> > > introduce a new BinaryKeyValue table and add binary metadata. >> > > >> > > On Wed, Jul 7, 2021 at 8:32 AM Nate Bauernfeind < >> > > natebauernfe...@deephaven.io> wrote: >> > > >> > > > Deephaven and I are very supportive of "upgrading" the value half of >> > > > the kv >> > > > pair to a byte vector. What is the best way to find out if there is >> > > > sufficient interest? >> > > > >> > > > >> > > > I've been stewing on the ideas here around schema evolution, and I >> > > > realize >> > > > the specific feature I am missing is the ability to encode that a field >> > > > (i.e. its FieldNode and accompanying Buffers in the RecordBatch) is >> > > > empty/has-no-data in O(0) cost (yes; for free). >> > > > >> > > > Might there be interest in adding a "field_id" to the FieldNode (which >> > > > is >> > > > encoded on the RecordBatch flatbuffer)? I see a simple >> > > > forward-compatible >> > > > upgrade (by either keying off of 0, or explicitly set the field >> > > > default to >> > > > -1) which would allow the sender to "skip" fields that have 1) >> > > > FieldNode >> > > > length of zero, and 2) all Buffer's associated at that level (and >> > > > further >> > > > nested) are also equally empty (i.e. Buffer length is zero). >> > > > >> > > > I understand this concept slightly interferes with RecordBatch's >> > > > `length` >> > > > field, and that many implementations use that length to resize the >> > > > root-level FieldNodes. The use-case I have in mind has different >> > > > logical >> > > > lengths per field node; current implementations require sending a >> > > > RecordBatch length of the max length across all root level field >> > > > nodes. I >> > > > believe this requires a copy of data whenever a field node is too >> > > > short; I >> > > > don't know if there is a decent solution to this slight inefficiency. >> > > > I am >> > > > bringing it up because if "skipping a field node when it is empty" is a >> > > > feature, then we may not want to allocate space for those nodes given >> > > > that >> > > > the record batch length will likely be greater than zero. >> > > > >> > > > On Wed, Jul 7, 2021 at 8:12 AM Wes McKinney <wesmck...@gmail.com> >> > > > wrote: >> > > > >> > > > > On Wed, Jul 7, 2021 at 2:53 PM David Li <apa...@lidavidm.me> wrote: >> > > > > > >> > > > > > From the Flatbuffers internals doc[1] it appears they are the same: >> > > > > "Strings are simply a vector of bytes, and are always >> > > > > null-terminated." >> > > > > >> > > > > I see. I took a look at flatbuffers.h, and it appears that changing >> > > > > this field from string to [byte] would be backward-compatible and >> > > > > forward-compatible except with code that expects a null terminator. >> > > > > This is something we could discuss separately if there were enough >> > > > > interest. >> > > > > >> > > > > > [1]: >> > > > > > https://google.github.io/flatbuffers/flatbuffers_internals.html >> > > > > > >> > > > > > -David >> > > > > > >> > > > > > On Wed, Jul 7, 2021, at 05:08, Wes McKinney wrote: >> > > > > > > On Tue, Jul 6, 2021 at 6:33 PM Micah Kornfield < >> > > > emkornfi...@gmail.com> >> > > > > wrote: >> > > > > > > > >> > > > > > > > > >> > > > > > > > > Right, I had wanted to focus the discussion on Flight as I >> > > > > > > > > think >> > > > > schema >> > > > > > > > > evolution or multiplexing streams (more so the latter) is a >> > > > > property of the >> > > > > > > > > transport and not the stream format itself. If we are leaning >> > > > > towards just >> > > > > > > > > schema evolution then maybe it makes sense to discuss it for >> > > > > > > > > the >> > > > > IPC stream >> > > > > > > > > format and leverage that in Flight. I'd be interested in what >> > > > > others think. >> > > > > > > > >> > > > > > > > I tend to agree, I think stream multiplexing is likely a >> > > > > > > > transport >> > > > > level >> > > > > > > > issue. IMO I think schema evolution should be consistent with >> > > > > > > > the >> > > > > IPC >> > > > > > > > stream format and flight. >> > > > > > > > >> > > > > > > > >> > > > > > > > > Nate: it may be worth starting a separate discussion about >> > > > > > > > > more >> > > > > general >> > > > > > > > > metadata in the IPC message. I'm not aware of why key-value >> > > > > metadata was >> > > > > > > > > chosen/if opaque bytes were considered in the past. >> > > > > > > > >> > > > > > > > >> > > > > > > > I think this was an unfortunate design of the key value >> > > > > > > > metadata >> > > > in >> > > > > > > > Schema.fbs, but I don't think I was around when this decision >> > > > > > > > was >> > > > > made. >> > > > > > > >> > > > > > > I agree that it's unfortunate that we did not use [ byte ] >> > > > > > > instead of >> > > > > > > string for the value in the KeyValue metadata — I think this was >> > > > > > > more >> > > > > > > of an oversight than a deliberate choice (e.g. it was not our >> > > > > > > intent >> > > > > > > to require binary data to be base64-encoded — this is something >> > > > > > > that >> > > > > > > we have to do when encoding binary data in Thrift KeyValue >> > > > > > > metadata >> > > > > > > for Parquet, for example). Is the binary representation of [byte] >> > > > > > > different from string? >> > > > > > > >> > > > > > > >> > > > > > > >> > > > > > > > Side Question: Why isn't the IPC stream format a series of the >> > > > flight >> > > > > > > > > protobufs? >> > > > > > > > >> > > > > > > > In addition to what David said, protobufs can't be read >> > > > > > > > directly >> > > > > from a >> > > > > > > > memory-mapped file (they need decoding). This was one of the >> > > > design >> > > > > > > > considerations of using flatbuffers and IPC Stream/File format. >> > > > > > > > >> > > > > > > > I was thinking Micah's comment is more that whatever we do, it >> > > > > should be >> > > > > > > > > clearly specified and edge cases should be considered, >> > > > > > > > > especially >> > > > > if we >> > > > > > > > > might want to 'backport' this into the stream format later. >> > > > > > > > >> > > > > > > > >> > > > > > > > Yes, for dictionaries we just need to be careful to define >> > > > semantics >> > > > > and >> > > > > > > > ensure implementations are validating them with regards to >> > > > > dictionaries. >> > > > > > > > There likely isn't any need to change current implementations >> > > > though. >> > > > > > > > >> > > > > > > > On Mon, Jun 28, 2021 at 1:25 PM David Li <lidav...@apache.org> >> > > > > wrote: >> > > > > > > > >> > > > > > > > > Right, I had wanted to focus the discussion on Flight as I >> > > > > > > > > think >> > > > > schema >> > > > > > > > > evolution or multiplexing streams (more so the latter) is a >> > > > > property of the >> > > > > > > > > transport and not the stream format itself. If we are leaning >> > > > > towards just >> > > > > > > > > schema evolution then maybe it makes sense to discuss it for >> > > > > > > > > the >> > > > > IPC stream >> > > > > > > > > format and leverage that in Flight. I'd be interested in what >> > > > > others think. >> > > > > > > > > >> > > > > > > > > Especially if we are looking at multiplexing streams - I >> > > > > > > > > would >> > > > > wonder if >> > > > > > > > > that's actually better served by making it easier to >> > > > > > > > > implement >> > > > > using the >> > > > > > > > > Flight implementation as it stands (by managing concurrent >> > > > > > > > > RPC >> > > > > calls and/or >> > > > > > > > > performing the union-of-structs encoding trick for you), >> > > > > > > > > instead >> > > > > of having >> > > > > > > > > to change the protocol. >> > > > > > > > > >> > > > > > > > > Nate: it may be worth starting a separate discussion about >> > > > > > > > > more >> > > > > general >> > > > > > > > > metadata in the IPC message. I'm not aware of why key-value >> > > > > metadata was >> > > > > > > > > chosen/if opaque bytes were considered in the past. Off the >> > > > > > > > > top >> > > > of >> > > > > my head >> > > > > > > > > if it's for on-disk storage and fully application-defined it >> > > > > > > > > may >> > > > > make sense >> > > > > > > > > to store as a separate file alongside the Arrow file >> > > > > > > > > (indexed by >> > > > > record >> > > > > > > > > batch index) where you can take advantage of whatever format >> > > > > > > > > is >> > > > > most >> > > > > > > > > suitable. >> > > > > > > > > >> > > > > > > > > -David >> > > > > > > > > >> > > > > > > > > On Sun, Jun 27, 2021, at 07:50, Gosh Arzumanyan wrote: >> > > > > > > > > > Hi guys, >> > > > > > > > > > >> > > > > > > > > > 1. Regarding IPC vs Flight: in fact my initial suggestion >> > > > > > > > > > was >> > > > to >> > > > > add this >> > > > > > > > > > feature starting from the IPC(I moved initial write up >> > > > > > > > > > steps to >> > > > > the >> > > > > > > > > bottom >> > > > > > > > > > of the doc). Afterwards David suggested focusing on Flight >> > > > > > > > > > and >> > > > > that's how >> > > > > > > > > > we ended up with the protobufs change in the proposal. This >> > > > > being said I >> > > > > > > > > do >> > > > > > > > > > think that the place where this should be impemented is a >> > > > > > > > > > good >> > > > > question >> > > > > > > > > on >> > > > > > > > > > its own. Maybe it makes sense to have this kind of a >> > > > > > > > > > feature in >> > > > > IPC and >> > > > > > > > > > somehow use it in Flight, maybe not. >> > > > > > > > > > 2. The point about dictionaries deserves a dedicated >> > > > > > > > > > section in >> > > > > the >> > > > > > > > > > proposal. Nate and David brought it up and shared some >> > > > insights. >> > > > > I'll try >> > > > > > > > > > to aggregate them and we can continue the discussion form >> > > > there. >> > > > > > > > > > >> > > > > > > > > > Cheers, >> > > > > > > > > > Gosh >> > > > > > > > > > >> > > > > > > > > > On Sat., 26 Jun. 2021, 17:26 Nate Bauernfeind, < >> > > > > > > > > natebauernfe...@deephaven.io> >> > > > > > > > > > wrote: >> > > > > > > > > > >> > > > > > > > > > > > >> > > > > > > > > > > > > > makes it more difficult to bring schema evolution >> > > > > > > > > > > > > > back >> > > > > into the >> > > > > > > > > > > > > > IPC Stream format (i.e. it would live only in >> > > > > > > > > > > > > > flight) >> > > > > > > > > > > > > >> > > > > > > > > > > > > Gosh's proposal extends the flatbuffer structures >> > > > > > > > > > > > > not the >> > > > > > > > > protobufs. >> > > > > > > > > > > Can >> > > > > > > > > > > > > you help me understand how difficult it would be to >> > > > > > > > > > > > > bring >> > > > > the >> > > > > > > > > > > `schema_id` >> > > > > > > > > > > > > approach to the IPC stream format? >> > > > > > > > > > > > >> > > > > > > > > > > > I thought we were talking solely about the Flight >> > > > > > > > > > > > Protobuf >> > > > > > > > > definitions - >> > > > > > > > > > > > not the Flatbuffers (and the Google doc at least only >> > > > > > > > > > > > talks >> > > > > about the >> > > > > > > > > > > > Protobufs). >> > > > > > > > > > > > >> > > > > > > > > > > >> > > > > > > > > > > I somehow missed that schema_id is being added to >> > > > > > > > > > > protobuf in >> > > > > the >> > > > > > > > > document. >> > > > > > > > > > > It feels to me that the schema_id is a property that >> > > > > > > > > > > would >> > > > > ideally only >> > > > > > > > > > > apply to the RecordBatch. I better understand Micah's >> > > > > dictionary >> > > > > > > > > concerns, >> > > > > > > > > > > now, too. >> > > > > > > > > > > >> > > > > > > > > > > > Side Question: Why isn't the IPC stream format a >> > > > > > > > > > > > series of >> > > > > the flight >> > > > > > > > > > > > > protobufs? It's a real shame that there is no >> > > > > > > > > > > > > standard >> > > > way >> > > > > to >> > > > > > > > > > > > > capture/replay a stream with app_metadata. (Obviously >> > > > > ignoring the >> > > > > > > > > > > > > annoyances around protobuf wrapping flatbuffers.) >> > > > > > > > > > > > >> > > > > > > > > > > > The IPC format was defined long before Flight, and >> > > > > > > > > > > > Flight's >> > > > > > > > > app_metadata >> > > > > > > > > > > > was added after Flight's initial definition. Note an >> > > > > > > > > > > > IPC >> > > > > message does >> > > > > > > > > > > have >> > > > > > > > > > > > a provision for key-value metadata, though I think >> > > > > > > > > > > > APIs for >> > > > > that are >> > > > > > > > > not >> > > > > > > > > > > > fully exposed. (See ARROW-6940: >> > > > > > > > > > > > https://issues.apache.org/jira/browse/ARROW-6940 and >> > > > > despite my >> > > > > > > > > comments >> > > > > > > > > > > > there perhaps we need to unify or at least consider how >> > > > > Flight's >> > > > > > > > > > > > app_metadata relates to the IPC message >> > > > > > > > > > > > custom_metadata. >> > > > Also >> > > > > > > > > perhaps see >> > > > > > > > > > > > ARROW-1059.) >> > > > > > > > > > > > >> > > > > > > > > > > >> > > > > > > > > > > KeyValue unfortunately is string to string. In flatbuffer >> > > > > strings are >> > > > > > > > > only >> > > > > > > > > > > UTF-8 or 7-bit ASCII. The app_metadata on the other hand >> > > > > > > > > > > is >> > > > > opaque >> > > > > > > > > bytes. >> > > > > > > > > > > The latter is a bit more useful. >> > > > > > > > > > > >> > > > > > > > > > > -- >> > > > > > > > > > > >> > > > > > > > > > >> > > > > > > > > >> > > > > > > >> > > > > >> > > > >> > > > >> > > > -- >> > > >
