Thanks for the careful consideration here, everyone. I completely agree that we do not want this to be confused as setting a precedent about delegating design decisions. I don't think the Delta community would do that either! We have to make decisions that are right for Iceberg.
It sounds like we're mostly in agreement on both of Russell's concerns. The value of compatibility in this case likely overrides the pain and annoyance. I'll update the spec PRs so that we can move forward. Ryan On Mon, Oct 21, 2024 at 3:05 PM Szehon Ho <szehon...@apple.com.invalid> wrote: > Im +1 for adding DV (Goal 1) and also +1 for the ability for Iceberg > readers to read Delta Lake DV’s, as the magic byte, CRC make sense > design-wise (Goal 2). > > Its nice that there's cross-community collaboration probably in other > areas Im not looking at, but I'm -0.5 on writing an otherwise unjustifiable > (albeit small) format change to be compatible by Delta Lake readers (Goal > 3), to register that this is irregular direction for the project, for > Iceberg to choose a spec just so it can be read by another project. For > example, it can be debated, but discussions in the past about adding export > functionality to Hive, were not supported to be added to Iceberg project. > So it won’t block if community supports it, but want to raise awareness. > > Thanks, > Szehon > > > > On Oct 21, 2024, at 2:36 PM, Micah Kornfield <emkornfi...@gmail.com> > wrote: > > I agree with everything Russell said. I think we should move forward with > the current format of DVs to favor compatibility. I'll add that I think > the collaboration aspect likely applies to other aspects as well outside of > Deletion Vectors (e.g. the work that is happening on Variant type). > > Thanks, > Micah > > On Mon, Oct 21, 2024 at 1:45 PM Russell Spitzer <russell.spit...@gmail.com> > wrote: > >> I've thought about this a lot and talked it over with a lot of folks. As >> I've noted before my main concerns are >> >> A. Setting a precedent that we are delegating design decisions to another >> project >> B. Setting unnecessary requirements that can only really be checked by >> integration tests with another system >> >> I think the value of compatibility can override the pain/annoyance of B. >> >> For A, I just want to make clear I will not go along with any sort of >> concession in design in the future. I think it's ok that we do it this >> time, but in the future if the Delta Delete Vector format changes I would >> really hope that the community around Delta would make those decisions in >> collaboration with the Apache Iceberg community. This is probably to be a >> red line for me in the future and I won't be able to go ahead in the future >> with any changes that aren't necessary for the Iceberg project regardless >> of their adoption in other formats. >> >> So with that said, I'm in support of any of the above solutions but I >> think just going with full compatibility with Delta (down to storage format >> details) is the right choice to try to get the two communities working >> together in the future. >> >> On Sat, Oct 19, 2024 at 4:38 PM rdb...@gmail.com <rdb...@gmail.com> >> wrote: >> >>> Thanks for the summary, Szehon! >>> >>> I would add one thing to the "minimum" for each option. Because we want >>> to be able to seek directly to the DV for a particular data file, I think >>> it's important to start the blob with magic bytes. That way the reader can >>> validate that the offset was correct and that the contents of the blob are >>> in the expected format. So I'd add magic bytes to options (1) and (2). In >>> (2) we would want the magic bytes to match the ones from Delta to be able >>> to read DV files written by Delta. >>> >>> Ryan >>> >>> On Thu, Oct 17, 2024 at 8:55 PM Szehon Ho <szehon.apa...@gmail.com> >>> wrote: >>> >>>> So based on Micah's original goals, switch 2 and 3: >>>> >>>> 1. The best possible implementation of DVs (limited redundancy, no >>>> extraneous fields, CPU efficiency, minimal space, etc). >>>> 2. The ability for Iceberg readers to read Delta Lake DVs >>>> 3. The ability for Delta Lake readers to read Iceberg DVs >>>> >>>> The minimum for each option are: >>>> (1) = DV >>>> (2) = DV (little-endian) + CRC (big-endian) >>>> (3) = Len (big-endian) + Magic + DV (litte-endian) + CRC (big-endian) >>>> >>>> Design wise, CRC can be useful, Magic may be useful/OK, but Len is >>>> controversial as its a different length than the bounding Puffin length >>>> (uncompressed and also a partial length without CRC). Big-endian Len/CRC >>>> is not ideal. >>>> >>>> I hope thats right? As it took me somet ime to go through the thread, >>>> hope it saves others some time too. >>>> Thanks >>>> Szehon >>>> >>>> >>>> On Thu, Oct 17, 2024 at 4:16 PM Anton Okolnychyi <aokolnyc...@gmail.com> >>>> wrote: >>>> >>>>> For the conversion from Delta to Iceberg, wouldn't we need to scan all >>>>>> of the Delta Vectors if we choose a different CRC or other endian-ness? >>>>> >>>>> >>>>> Exactly, we would not be able to expose Delta as Iceberg if we choose >>>>> a different checksum type or byte order. >>>>> >>>>> Does delta mandate that writers also include this information in their >>>>>> metadata files? >>>>> >>>>> >>>>> If I understand correctly, the checksum is only in the DV file, not in >>>>> the metadata. >>>>> >>>>> - Anton >>>>> >>>>> чт, 17 жовт. 2024 р. о 14:51 Russell Spitzer < >>>>> russell.spit...@gmail.com> пише: >>>>> >>>>>> For the conversion from Delta to Iceberg, wouldn't we need to scan >>>>>> all of the Delta Vectors if we choose a different CRC or other >>>>>> endian-ness? >>>>>> Does delta mandate that writers also include this information in their >>>>>> metadata files? >>>>>> >>>>>> On Thu, Oct 17, 2024 at 4:26 PM Anton Okolnychyi < >>>>>> aokolnyc...@gmail.com> wrote: >>>>>> >>>>>>> We would want to have magic bytes + checksum as part of the blob in >>>>>>> Iceberg, as discussed in the spec PRs. If we chose something other than >>>>>>> CRC >>>>>>> and/or use little endian for all parts of the blob, this would break the >>>>>>> compatibility in either direction and would prevent the use case that >>>>>>> Scott >>>>>>> was mentioning. >>>>>>> >>>>>>> - Anton >>>>>>> >>>>>>> чт, 17 жовт. 2024 р. о 08:58 Bart Samwel <b...@databricks.com.invalid> >>>>>>> пише: >>>>>>> >>>>>>>> I hope it's OK if I chime in. I'm one of the people responsible for >>>>>>>> the format for position deletes that is used in Delta Lake and I've >>>>>>>> been >>>>>>>> reading along with the discussion. Given that the main sticking point >>>>>>>> is >>>>>>>> whether this compatibility is worth the associated "not pure" spec, I >>>>>>>> figured that maybe I can mention what the consequences would be for the >>>>>>>> Delta Lake developers and users, depending on the outcome of this >>>>>>>> discussion. I can also give some historical background, in case people >>>>>>>> find >>>>>>>> that interesting. >>>>>>>> >>>>>>>> 1) Historical background on why the Delta Lake format is the way it >>>>>>>> is. >>>>>>>> >>>>>>>> The reason that this length field was added on the Delta Lake side >>>>>>>> is because we didn't have a framing format like Puffin. Like you, we >>>>>>>> wanted >>>>>>>> the Deletion Vector files to be parseable by themselves, if only for >>>>>>>> debugging purposes. If we could go back, then we might have adopted >>>>>>>> Puffin. >>>>>>>> Or we would have made the pointers in the metadata point at only the >>>>>>>> blob + >>>>>>>> CRC, and kept the length outside of it, in the framing format. But the >>>>>>>> reality is that right now there are many clients out there that read >>>>>>>> the >>>>>>>> current format, and we can't change this anymore. :( The endianness >>>>>>>> difference is simply an unfortunate historical accident. They are at >>>>>>>> different layers, and this was the first time we really did anything >>>>>>>> binary-ish in Delta Lake, so we didn't actually have any consistent >>>>>>>> baseline to be consistent with. We only noticed the difference once it >>>>>>>> had >>>>>>>> "escaped" into the wild, and then it was too late. >>>>>>>> >>>>>>>> Am I super happy with it? No. Is it *terrible*? Well, not terrible >>>>>>>> enough for us to go back and upgrade the protocol to fix it. It doesn't >>>>>>>> lead to broken behavior. This is just a historical idiosyncrasy, and >>>>>>>> the >>>>>>>> friction caused by protocol changes is much higher than any benefit >>>>>>>> from a >>>>>>>> cleaner spec. So basically, we're stuck with it until the next time we >>>>>>>> do a >>>>>>>> major overhaul of the protocol. >>>>>>>> >>>>>>>> (2) What are the consequences for Delta Lake if this is *not* made >>>>>>>> compatible? >>>>>>>> >>>>>>>> Well, then we'd have to support this new layout in Delta Lake. This >>>>>>>> would be a long and relatively painful process. >>>>>>>> >>>>>>>> It would not just be a matter of "retconning" it into the protocol >>>>>>>> and updating the libraries. There are simply too many connectors out >>>>>>>> there, >>>>>>>> owned by different vendors etc. Until they would adopt the change, they >>>>>>>> would simply error out on these files *at runtime with weird >>>>>>>> errors*, or potentially even use the invalid values and crash and >>>>>>>> burn. (Lack of proper input validation is unfortunately a real thing >>>>>>>> in the >>>>>>>> wild.) >>>>>>>> >>>>>>>> So instead, what we would do is to add this in a new protocol >>>>>>>> version of Delta Lake. Or actually, it would be a "table feature", >>>>>>>> since >>>>>>>> Delta Lake has a-la-carte protocol features. But these features tend to >>>>>>>> take a long time to fully permeate the connector ecosystem, and people >>>>>>>> don't actually upgrade their systems very quickly. That means that >>>>>>>> realistically, nobody would be able to make use of this for quite a >>>>>>>> while. >>>>>>>> >>>>>>>> So what would need to happen instead? For now we would have to >>>>>>>> rewrite the delete files on conversion, only to add this annoying >>>>>>>> little >>>>>>>> length field. This would add at least 200 ms of latency to any metadata >>>>>>>> conversion, if only because of the cloud object storage GET and PUT >>>>>>>> latency. Furthermore, the conversion latency for a single commit would >>>>>>>> become dependent on the number of delete files instead of being O(1). >>>>>>>> And >>>>>>>> it would take significant development time to actually make this work >>>>>>>> and >>>>>>>> to make this scale. >>>>>>>> >>>>>>>> Based on these consequences, you can imagine why I would *really* >>>>>>>> appreciate it if the community could weigh this aspect as part of their >>>>>>>> deliberations. >>>>>>>> >>>>>>>> (3) Is Iceberg -> Delta Lake compatibility actually important >>>>>>>> enough to care about? >>>>>>>> >>>>>>>> From where I'm standing, compatibility is nearly always very >>>>>>>> important. It's not important for users who have standardized fully on >>>>>>>> Iceberg, and those are probably the most represented here in the dev >>>>>>>> community. But in the world that I'm seeing, companies are generally >>>>>>>> using >>>>>>>> a mixture of many different systems, and they are suffering because of >>>>>>>> the >>>>>>>> inability for systems to operate efficiently on each others' data. >>>>>>>> Being >>>>>>>> able to convert easily and efficiently in both directions benefits >>>>>>>> users. >>>>>>>> In this case it's about Iceberg and Delta Lake, but IMO this is true >>>>>>>> as a >>>>>>>> principle regardless of which systems you're talking about -- lower >>>>>>>> friction for interoperability is very high value because it increases >>>>>>>> users' choice in the tools that they can use -- it allows them to >>>>>>>> choose >>>>>>>> the right tool for the job at hand. And it doesn't matter if users are >>>>>>>> converting from Delta Lake to Iceberg or the other way around, they >>>>>>>> are in >>>>>>>> fact all Iceberg users! >>>>>>>> >>>>>>>> Putting it simply: I have heard many users complain that they can't >>>>>>>> (efficiently) read data from system X in system Y. At the same time, I >>>>>>>> have >>>>>>>> never heard a user complaining about having inconsistent endianness in >>>>>>>> their protocols. >>>>>>>> >>>>>>>> On Thu, Oct 17, 2024 at 11:02 AM Jean-Baptiste Onofré < >>>>>>>> j...@nanthrax.net> wrote: >>>>>>>> >>>>>>>>> Hi folks, >>>>>>>>> >>>>>>>>> As Daniel said, I think we have actually two proposals in one: >>>>>>>>> 1. The first proposal is "improvement of positional delete files", >>>>>>>>> using delete vectors stored in Puffin files. I like this proposal, >>>>>>>>> it >>>>>>>>> makes a lot of sense. I think with a kind of consensus here (we >>>>>>>>> discussed about how to parse Puffin files, etc, good discussion). >>>>>>>>> 2. Then, based on (1), is support vector format "compatible" with >>>>>>>>> Delta. This is also interesting. However, do we really need this in >>>>>>>>> Spec V3 ? Why not focus on the original proposal (improvement of >>>>>>>>> positional delete) with a simple approach, and evaluate Delta >>>>>>>>> compatibility later ? If the compatibility is "easy", I'm not >>>>>>>>> against >>>>>>>>> to include in V3, but users might be disappointed if bringing this >>>>>>>>> means a tradeoff. >>>>>>>>> >>>>>>>>> Imho, I will focus on 1 because it would be a great feature for the >>>>>>>>> Iceberg community. >>>>>>>>> >>>>>>>>> Regards >>>>>>>>> JB >>>>>>>>> >>>>>>>>> On Wed, Oct 16, 2024 at 9:16 PM Daniel Weeks <dwe...@apache.org> >>>>>>>>> wrote: >>>>>>>>> > >>>>>>>>> > Hey Everyone, >>>>>>>>> > >>>>>>>>> > I feel like at this point we've articulated all of the various >>>>>>>>> options and paths forward, but this really just comes down to a >>>>>>>>> matter of >>>>>>>>> whether we want to make a concession here for the purpose of >>>>>>>>> compatibility. >>>>>>>>> > >>>>>>>>> > If we were building this with no prior art, I would expect to >>>>>>>>> omit the length and align the endianness, but given there's an >>>>>>>>> opportunity >>>>>>>>> to close the gap with minor inefficiency, it merits real >>>>>>>>> consideration. >>>>>>>>> > >>>>>>>>> > This proposal takes into consideration bi-directional >>>>>>>>> compatibility while maintaining backward compatibility. Do we feel >>>>>>>>> this is >>>>>>>>> beneficial to the larger community or should we discard efforts for >>>>>>>>> compatibility? >>>>>>>>> > >>>>>>>>> > -Dan >>>>>>>>> > >>>>>>>>> > On Wed, Oct 16, 2024 at 11:01 AM rdb...@gmail.com < >>>>>>>>> rdb...@gmail.com> wrote: >>>>>>>>> >> >>>>>>>>> >> Thanks, Russell for the clear summary of the pros and cons! I >>>>>>>>> agree there's some risk to Iceberg implementations, but I think that >>>>>>>>> is >>>>>>>>> mitigated somewhat by code reuse. For example, an engine like Trino >>>>>>>>> could >>>>>>>>> simply reuse code for reading Delta bitmaps, so we would get some >>>>>>>>> validation and support more easily. >>>>>>>>> >> >>>>>>>>> >> Micah, I agree with the requirements that you listed, but I >>>>>>>>> would say #2 is not yet a "requirement" for the design. It's a >>>>>>>>> consideration that I think has real value, but it's up to the >>>>>>>>> community >>>>>>>>> whether we want to add some cost to #1 to make #2 happen. I definitely >>>>>>>>> think that #3 is a requirement so that we can convert Delta to Iceberg >>>>>>>>> metadata (as in the iceberg-delta-lake module). >>>>>>>>> >> >>>>>>>>> >> For the set of options, I would collapse a few of those options >>>>>>>>> because I think that we would use the same bitmap representation, the >>>>>>>>> portable 64-bit roaring bitmap. >>>>>>>>> >> >>>>>>>>> >> If that's the case (and probably even if we had some other >>>>>>>>> representation), then Delta can always add support for reading Iceberg >>>>>>>>> delete vectors. That means we either go with the current proposal (a) >>>>>>>>> that >>>>>>>>> preserves the ability for existing Delta clients to read, or we go >>>>>>>>> with a >>>>>>>>> different proposal that we think is better, in which case Delta adds >>>>>>>>> support. >>>>>>>>> >> >>>>>>>>> >> I think both options (c) and (d) have the same effect: Delta >>>>>>>>> readers need to change and that breaks forward compatibility. >>>>>>>>> Specifically: >>>>>>>>> >> * I think that Option (c) would mean that we set the offset to >>>>>>>>> either magic bytes or directly to the start of the roaring bitmap, so >>>>>>>>> I >>>>>>>>> think we will almost certainly be able to read Delta DVs. Even if we >>>>>>>>> didn't >>>>>>>>> have a similar bitmap encoding, we would probably end up adding >>>>>>>>> support for >>>>>>>>> reading Delta DVs for iceberg-delta-lake. Then it's a question of >>>>>>>>> whether >>>>>>>>> support for converted files is required -- similar to how we handle >>>>>>>>> missing >>>>>>>>> partition values in data files from Hive tables that we just updated >>>>>>>>> the >>>>>>>>> spec to clarify. >>>>>>>>> >> * Option (d) is still incompatible with existing Delta readers, >>>>>>>>> so there isn't much of a difference between this and (b) >>>>>>>>> >> >>>>>>>>> >> To me, Micah's requirement #2 is a good goal, but needs to be >>>>>>>>> balanced against the cost. I don't see that cost as too high, and I >>>>>>>>> think >>>>>>>>> avoiding fragmentation across the projects helps us work together >>>>>>>>> more in >>>>>>>>> the future. But again, that may be my goal and not a priority for the >>>>>>>>> broader Iceberg community. >>>>>>>>> >> >>>>>>>>> >> Ryan >>>>>>>>> >> >>>>>>>>> >> On Wed, Oct 16, 2024 at 10:10 AM Micah Kornfield < >>>>>>>>> emkornfi...@gmail.com> wrote: >>>>>>>>> >>> >>>>>>>>> >>> One small point >>>>>>>>> >>>> >>>>>>>>> >>>> Theoretically we could end up with iceberg implementers who >>>>>>>>> have bugs in this part of the code and we wouldn’t even know it was an >>>>>>>>> issue till someone converted the table to delta. >>>>>>>>> >>> >>>>>>>>> >>> >>>>>>>>> >>> I guess we could mandate readers validate all fields here to >>>>>>>>> make sure they are all consistent, even if unused. >>>>>>>>> >>> >>>>>>>>> >>> Separately, I think it might pay to take a step back and >>>>>>>>> restate desired requirements of this design (in no particular order): >>>>>>>>> >>> 1. The best possible implementation of DVs (limited >>>>>>>>> redundancy, no extraneous fields, CPU efficiency, minimal space, etc). >>>>>>>>> >>> 2. The ability for Delta Lake readers to read Iceberg DVs >>>>>>>>> >>> 3. The ability for Iceberg readers to read Delta Lake DVs >>>>>>>>> >>> >>>>>>>>> >>> The current proposal accomplishes 2 and 3 at very low cost >>>>>>>>> with some for cost for 1. I still think 1 is important. Table >>>>>>>>> formats are >>>>>>>>> still going through a very large growth phase so taking suboptimal >>>>>>>>> choices, >>>>>>>>> when there are better choices that don't add substantial cost, >>>>>>>>> shouldn't be >>>>>>>>> done lightly. Granted DVs are only going to be a very small part of >>>>>>>>> the >>>>>>>>> cost of any table format. >>>>>>>>> >>> >>>>>>>>> >>> I think it is worth discussing other options to see if we >>>>>>>>> think there is a better one (if there isn't then I would propose we >>>>>>>>> continue with the current proposal). Please chime in if I missed one >>>>>>>>> but >>>>>>>>> off the top of my head these are: >>>>>>>>> >>> >>>>>>>>> >>> a. Go forward with current proposal >>>>>>>>> >>> b. Create a different format DV that we feel is a better, and >>>>>>>>> take no additional steps for compatibility with Delta Lake. >>>>>>>>> >>> c. Create a different format DV that we feel is a better, and >>>>>>>>> allow backwards compatibility by adding "reader" support for Delta >>>>>>>>> Lake DVs >>>>>>>>> in the spec, but not "writer support". >>>>>>>>> >>> d. Go forward with the current proposal but use offset and >>>>>>>>> length to trim off the "offset" bytes. (I assume this would break >>>>>>>>> Delta >>>>>>>>> Lake Readers but I think Iceberg Readers could still read Delta Lake >>>>>>>>> tables). This option is very close to C but doesn't address all >>>>>>>>> concerns >>>>>>>>> around DV format). >>>>>>>>> >>> >>>>>>>>> >>> Out of these three, my slight preference would be option c >>>>>>>>> (add migration capabilities from Delta Lake to Iceberg), followed by >>>>>>>>> option >>>>>>>>> a (current proposal). >>>>>>>>> >>> >>>>>>>>> >>> Cheers, >>>>>>>>> >>> Micah >>>>>>>>> >>> >>>>>>>>> >>> >>>>>>>>> >>> >>>>>>>>> >>> >>>>>>>>> >>> >>>>>>>>> >>> On Tue, Oct 15, 2024 at 9:32 PM Russell Spitzer < >>>>>>>>> russell.spit...@gmail.com> wrote: >>>>>>>>> >>>> >>>>>>>>> >>>> @Scott We would have the ability to read delta vectors >>>>>>>>> regardless of what we pick since on Iceberg side we really just need >>>>>>>>> the >>>>>>>>> bitmap and what offset it is located at within a file, everything else >>>>>>>>> could be in the Iceberg metadata. We don’t have any disagreement on >>>>>>>>> this >>>>>>>>> aspect I think. >>>>>>>>> >>>> >>>>>>>>> >>>> The question is whether we would write additional Delta >>>>>>>>> specific metadata into the vector itself that an Iceberg >>>>>>>>> implementation >>>>>>>>> would not use so that current Delta readers could read Iceberg delete >>>>>>>>> vectors without a code change or rewriting the vectors. The underlying >>>>>>>>> representation would still be the same between the two formats. >>>>>>>>> >>>> >>>>>>>>> >>>> The pros to doing this are that a reverse translation of >>>>>>>>> iceberg to delta would be much simpler. Any implementers who already >>>>>>>>> have >>>>>>>>> delta vector read code can probably mostly reuse it although our >>>>>>>>> metadata >>>>>>>>> would let them skip to just reading the bitmap. >>>>>>>>> >>>> >>>>>>>>> >>>> The cons are that the metadata being written isn’t used by >>>>>>>>> Iceberg so any real tests would require using a delta reader, >>>>>>>>> anything else >>>>>>>>> would just be synthetic. Theoretically we could end up with iceberg >>>>>>>>> implementers who have bugs in this part of the code and we wouldn’t >>>>>>>>> even >>>>>>>>> know it was an issue till someone converted the table to delta. Other >>>>>>>>> iceberg readers would just be ignoring these bytes, so we essentially >>>>>>>>> are >>>>>>>>> adding a requirement and complexity (although not that much) to >>>>>>>>> Iceberg >>>>>>>>> writers for the benefit of current Delta readers. Delta would >>>>>>>>> probably also >>>>>>>>> have to add a new fields to their metadata representations to capture >>>>>>>>> the >>>>>>>>> vector metadata to handle our bitmaps. >>>>>>>>> >>>> >>>>>>>>> >>>> On Tue, Oct 15, 2024 at 5:56 PM Scott Cowell < >>>>>>>>> scott.cow...@dremio.com.invalid> wrote: >>>>>>>>> >>>>> >>>>>>>>> >>>>> From an engine perspective I think compatibility between >>>>>>>>> Delta and Iceberg on DVs is a great thing to have. The additions for >>>>>>>>> cross-compat seem a minor thing to me that is vastly outweighed by a >>>>>>>>> future >>>>>>>>> where Delta tables with DVs were supported in Delta Uniform and could >>>>>>>>> be >>>>>>>>> read by any Iceberg V3 compliant engine. >>>>>>>>> >>>>> >>>>>>>>> >>>>> -Scott >>>>>>>>> >>>>> >>>>>>>>> >>>>> On Tue, Oct 15, 2024 at 2:06 PM Anton Okolnychyi < >>>>>>>>> aokolnyc...@gmail.com> wrote: >>>>>>>>> >>>>>> >>>>>>>>> >>>>>> Are there engines/vendors/companies in the community that >>>>>>>>> support both Iceberg and Delta and would benefit from having one blob >>>>>>>>> layout for DVs? >>>>>>>>> >>>>>> >>>>>>>>> >>>>>> - Anton >>>>>>>>> >>>>>> >>>>>>>>> >>>>>> вт, 15 жовт. 2024 р. о 11:10 rdb...@gmail.com < >>>>>>>>> rdb...@gmail.com> пише: >>>>>>>>> >>>>>>> >>>>>>>>> >>>>>>> Thanks, Szehon. >>>>>>>>> >>>>>>> >>>>>>>>> >>>>>>> To clarify on compatibility, using the same format for the >>>>>>>>> blobs makes it so that existing Delta readers can read and use the DVs >>>>>>>>> written by Iceberg. I'd love for Delta to adopt Puffin, but if we >>>>>>>>> adopt the >>>>>>>>> extra fields they would not need to change how readers work. That's >>>>>>>>> why I >>>>>>>>> think there is a benefit to using the same format. We avoid >>>>>>>>> fragmentation >>>>>>>>> and make sure data and delete files are compatible. No unnecessary >>>>>>>>> fragmentation. >>>>>>>>> >>>>>>> >>>>>>>>> >>>>>>> Ryan >>>>>>>>> >>>>>>> >>>>>>>>> >>>>>>> On Tue, Oct 15, 2024 at 10:57 AM Szehon Ho < >>>>>>>>> szehon.apa...@gmail.com> wrote: >>>>>>>>> >>>>>>>> >>>>>>>>> >>>>>>>> This is awesome work by Anton and Ryan, it looks like a >>>>>>>>> ton of effort has gone into the V3 position vector proposal to make it >>>>>>>>> clean and efficient, a long time coming and Im truly excited to see >>>>>>>>> the >>>>>>>>> great improvement in storage/perf. >>>>>>>>> >>>>>>>> >>>>>>>>> >>>>>>>> wrt to these fields, I think most of the concerns are >>>>>>>>> already mentioned by the other community members in the prs >>>>>>>>> https://github.com/apache/iceberg/pull/11238 and >>>>>>>>> https://github.com/apache/iceberg/pull/11238, so not much to >>>>>>>>> add. The DV itself is RoaringBitmap 64-bit format so that's great, >>>>>>>>> the >>>>>>>>> argument for CRC seems reasonable, and I dont have enough data to be >>>>>>>>> opinionated towards endian/magic byte. >>>>>>>>> >>>>>>>> >>>>>>>>> >>>>>>>> But I do lean towards the many PR comments that the extra >>>>>>>>> length field is unnecessary, and would just add confusion. It seemed >>>>>>>>> to me >>>>>>>>> that the Iceberg community has made so much effort to trim to spec to >>>>>>>>> the >>>>>>>>> bare minimum for cleanliness and efficiency, so I do feel the field >>>>>>>>> is not >>>>>>>>> in the normal direction of the project. Also Im not clear on the >>>>>>>>> plan for >>>>>>>>> old Delta readers, they cant read Puffin anyway, if Delta adopts >>>>>>>>> Puffin, >>>>>>>>> then new readers could adopt? Anyway great work again, thanks for >>>>>>>>> raising >>>>>>>>> the issue on devlist! >>>>>>>>> >>>>>>>> >>>>>>>>> >>>>>>>> Thanks, >>>>>>>>> >>>>>>>> Szehon >>>>>>>>> >>>>>>>> >>>>>>>>> >>>>>>>> On Mon, Oct 14, 2024 at 5:14 PM rdb...@gmail.com < >>>>>>>>> rdb...@gmail.com> wrote: >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> > I think it might be worth mentioning the current >>>>>>>>> proposal makes some, mostly minor, design choices to try to be >>>>>>>>> compatible >>>>>>>>> with Delta Lake deletion vectors. >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> Yes it does, and thanks for pointing this out, Micah. I >>>>>>>>> think it's important to consider whether compatibility is important >>>>>>>>> to this >>>>>>>>> community. I just replied to Piotr on the PR, but I'll adapt some of >>>>>>>>> that >>>>>>>>> response here to reach the broader community. >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> I think there is value in supporting compatibility with >>>>>>>>> older Delta readers, but I acknowledge that this may be my perspective >>>>>>>>> because my employer has a lot of Delta customers that we are going to >>>>>>>>> support now and in the future. >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> The main use case for maintaining compatibility with the >>>>>>>>> Delta format is that it's hard to move old jobs to new code in a >>>>>>>>> migration. >>>>>>>>> We see a similar issue in Hive to Iceberg migrations, where unknown >>>>>>>>> older >>>>>>>>> readers prevent migration entirely because they are hard to track >>>>>>>>> down and >>>>>>>>> often read files directly from the backing object store. I'd like to >>>>>>>>> avoid >>>>>>>>> the same problem here, where all readers need to be identified and >>>>>>>>> migrated >>>>>>>>> at the same time. Compatibility with the format those readers expect >>>>>>>>> makes >>>>>>>>> it possible to maintain Delta metadata for them temporarily. That >>>>>>>>> increases >>>>>>>>> confidence that things won't randomly break and makes it easier to get >>>>>>>>> people to move forward. >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> The second reason for maintaining compatibility is that >>>>>>>>> we want for the formats to become more similar. My hope is that we >>>>>>>>> can work >>>>>>>>> across both communities and come up with a common metadata format in a >>>>>>>>> future version -- which explains my interest in smooth migrations. >>>>>>>>> Maintaining compatibility in cases like this builds trust and keeps >>>>>>>>> our >>>>>>>>> options open: if we have compatible data layers, then it's easier to >>>>>>>>> build >>>>>>>>> a compatible metadata layer. I'm hoping that if we make the blob >>>>>>>>> format >>>>>>>>> compatible, we can get the Delta community to start using Puffin for >>>>>>>>> better >>>>>>>>> self-describing delete files. >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> Other people may not share those goals, so I think it >>>>>>>>> helps to consider what is being compromised for this compatibility. I >>>>>>>>> don't >>>>>>>>> think it is too much. There are 2 additional fields: >>>>>>>>> >>>>>>>>> * A 4-byte length field (that Iceberg doesn't need) >>>>>>>>> >>>>>>>>> * A 4-byte CRC to validate the contents of the bitmap >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> There are also changes to how these would have been >>>>>>>>> added if the Iceberg community were building this independently. >>>>>>>>> >>>>>>>>> * Our initial version didn't include a CRC at all, but >>>>>>>>> now that we think it's useful compatibility means using a CRC-32 >>>>>>>>> checksum >>>>>>>>> rather than a newer one >>>>>>>>> >>>>>>>>> * The Delta format uses big endian for its fields (or >>>>>>>>> mixed endian if you consider RoaringBitmap is LE) >>>>>>>>> >>>>>>>>> * The magic bytes (added to avoid reading the Puffin >>>>>>>>> footer) would have been different >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> Overall, I don't think that those changes to what we >>>>>>>>> would have done are unreasonable. It's only 8 extra bytes and half of >>>>>>>>> them >>>>>>>>> are for a checksum that is a good idea. >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> I'm looking forward to what the rest of the community >>>>>>>>> thinks about this. Thanks for reviewing the PR! >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> Ryan >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> On Sun, Oct 13, 2024 at 10:45 PM Jean-Baptiste Onofré < >>>>>>>>> j...@nanthrax.net> wrote: >>>>>>>>> >>>>>>>>>> >>>>>>>>> >>>>>>>>>> Hi >>>>>>>>> >>>>>>>>>> >>>>>>>>> >>>>>>>>>> Thanks for the PRs ! I reviewed Anton's document, I >>>>>>>>> will do a pass on the PRs. >>>>>>>>> >>>>>>>>>> >>>>>>>>> >>>>>>>>>> Imho, it's important to get feedback from query >>>>>>>>> engines, as, if delete >>>>>>>>> >>>>>>>>>> vectors is not a problem per se (it's what we are using >>>>>>>>> as internal >>>>>>>>> >>>>>>>>>> representation), the use of Puffin files to store it is >>>>>>>>> "impactful" >>>>>>>>> >>>>>>>>>> for the query engines (probably some query engines >>>>>>>>> might need to >>>>>>>>> >>>>>>>>>> implement Puffin spec (read/write) using other language >>>>>>>>> than Java, for >>>>>>>>> >>>>>>>>>> instance Apache Impala). >>>>>>>>> >>>>>>>>>> >>>>>>>>> >>>>>>>>>> I like the proposal, I just hope we won't "surprise" >>>>>>>>> some query >>>>>>>>> >>>>>>>>>> engines with extra work :) >>>>>>>>> >>>>>>>>>> >>>>>>>>> >>>>>>>>>> Regards >>>>>>>>> >>>>>>>>>> JB >>>>>>>>> >>>>>>>>>> >>>>>>>>> >>>>>>>>>> On Thu, Oct 10, 2024 at 11:41 PM rdb...@gmail.com < >>>>>>>>> rdb...@gmail.com> wrote: >>>>>>>>> >>>>>>>>>> > >>>>>>>>> >>>>>>>>>> > Hi everyone, >>>>>>>>> >>>>>>>>>> > >>>>>>>>> >>>>>>>>>> > There seems to be broad agreement around Anton's >>>>>>>>> proposal to use deletion vectors in Iceberg v3, so I've opened two >>>>>>>>> PRs that >>>>>>>>> update the spec with the proposed changes. The first, PR #11238, adds >>>>>>>>> a new >>>>>>>>> Puffin blob type, delete-vector-v1, that stores a delete vector. The >>>>>>>>> second, PR #11240, updates the Iceberg table spec. >>>>>>>>> >>>>>>>>>> > >>>>>>>>> >>>>>>>>>> > Please take a look and comment! >>>>>>>>> >>>>>>>>>> > >>>>>>>>> >>>>>>>>>> > Ryan >>>>>>>>> >>>>>>>> >
