As you noted the main point we still need to decide on is whether to have a standard "shard" definition (e.g. manifest plan task) or to allow it to be opaque and specific to catalogs implementing the protocol. I've not replied because I keep coming back to this decision and I'm not sure whether the advantage is being clear about how it works (being explicit) or allowing implementations to differ (opaque). I'm skeptical that there will be other strategies.
But to move forward, I think we should go with the option that preserves flexibility. I think the spec should state that plan tasks (if we call them that) are a JSON object that should be sent as-is back to the REST service to be used. One more thing that I would also change is that I don't think the "plan" and "scan" endpoints make much sense. We refer to the "scan" portion of this as "planFiles" in the reference implementation, and "scan" is used for actually reading data. To be less confusing, I think that file scan tasks should be returned by a "plan" endpoint and the manifest plan tasks (or shards) should be returned by a "pre-plan" endpoint. Does anyone else like the names "pre-plan" and "plan" better? Ryan On Mon, Jan 29, 2024 at 12:02 PM Chertara, Rahil <rcher...@amazon.com.invalid> wrote: > Hi All hope everyone is doing well, > > > Wanted to revive the discussion around the Rest Table Scan API work. For a > refresher here is the original proposal: > https://docs.google.com/document/d/1FdjCnFZM1fNtgyb9-v9fU4FwOX4An-pqEwSaJe8RgUg/edit#heading=h.cftjlkb2wh4h > as well as the PR: https://github.com/apache/iceberg/pull/9252 > > > From the last messages on the thread, I believe Ryan and Jack were in > favor of having two distinct api endpoints /plan and /scan, as well as a > stricter json definition for the "shard”, here is an example below from > what was discussed. > > > *POST /v1/namespaces/ns/tables/t/plan *{ "filter": { "type": "in", > "term": "x", "values": [1, 2, 3] }, "select": ["x", "a.b"]} > > { "manifest-plan-tasks": [ > { "start": 0, "length": 1000, "manifest": { "path": > "s3://some/manifest.avro", ...}, "delete-manifests": [...] }, > { ... } > ]} > > > *POST /v1/namespaces/ns/tables/t/scan *{ "filter": {"type": "in", "term": > "x", "values": [1, 2, 3] }, > > "select": ["x", "a.b"], > "manifest-plan-task": { "start": 0, "length": 1000, "manifest": { > "path": "s3://some/manifest.avro", ...}, "delete-manifests": [...] } } > > { "file-scan-tasks": [...] } > > > *POST /v1/namespaces/ns/tables/t/scan *{ "filter": {"type": "in", "term": > "x", "values": [1, 2, 3] }, "select": ["x", "a.b"]} > > > { "file-scan-tasks": [...] } > > > > However IIRC Micah and Renjie had some concerns around this stricter > structure as this can make it harder to evolve in the future, as well as > some potential scalability challenges for larger tables that have many > manifest files. (Feel free to expand further on the concerns if my > understanding is incorrect). > > > > Would appreciate if the community can leave any more thoughts/feedback on > this thread, as well as on the google doc, and the PR. > > > > Regards, > Rahil Chertara > > > > *From: *Renjie Liu <liurenjie2...@gmail.com> > *Reply-To: *"dev@iceberg.apache.org" <dev@iceberg.apache.org> > *Date: *Thursday, December 21, 2023 at 10:35 PM > *To: *"dev@iceberg.apache.org" <dev@iceberg.apache.org> > *Subject: *RE: [EXTERNAL] Proposal for REST APIs for Iceberg table scans > > > > *CAUTION*: This email originated from outside of the organization. Do not > click links or open attachments unless you can confirm the sender and know > the content is safe. > > > > I share the same concern with Micah. The shard detail should be > implementation details of the server, rather than exposing directly to the > client. If the goal is to make things stateless, we just need to attach a > snapshot id + shard id, then a determined algorithm is supposed to give the > same result. Also another concern is for huge analytics tables, we may have > a lot of manifest files, which may lead to large traffic from the rest > server. > > > > On Thu, Dec 21, 2023 at 7:41 AM Micah Kornfield <emkornfi...@gmail.com> > wrote: > > Also +1 for having a more strict definition of the shard. Having arbitrary > JSON was basically what we experimented with a string shard ID, and we > ended up with something very similar to the manifest plan task you describe > in the serialized ID string. > > > > IIUC the proposal correctly, I'd actually be -0.0 on the stricter > structure. I think forcing a contract where it isn't strictly necessary > makes it harder to evolve the system in the future. For example it makes > it harder to address potential scalability problems in a transparent way > (e.g. extreme edge cases in cardinality between manifest files and delete > files). > > > > It also seems like it might overly constrain implementations (it is not > clear we should need to compute the mapping between delete file manifests > to data file manifests up front to start planning). > > > > On Tue, Dec 19, 2023 at 2:10 PM Jack Ye <yezhao...@gmail.com> wrote: > > +1 for having /plan and /scan, sounds like a good idea to separate those 2 > distinct actions. > > > > Also +1 for having a more strict definition of the shard. Having arbitrary > JSON was basically what we experimented with a string shard ID, and we > ended up with something very similar to the manifest plan task you describe > in the serialized ID string. > > > > So sounds like we are converging to the following APIs: > > > > > *POST /v1/namespaces/ns/tables/t/plan *{ "filter": { "type": "in", > "term": "x", "values": [1, 2, 3] }, "select": ["x", "a.b"]} > > { "manifest-plan-tasks": [ > { "start": 0, "length": 1000, "manifest": { "path": > "s3://some/manifest.avro", ...}, "delete-manifests": [...] }, > { ... } > ]} > > > *POST /v1/namespaces/ns/tables/t/scan *{ "filter": {"type": "in", "term": > "x", "values": [1, 2, 3] }, > > "select": ["x", "a.b"], > "manifest-plan-task": { "start": 0, "length": 1000, "manifest": { > "path": "s3://some/manifest.avro", ...}, "delete-manifests": [...] } } > > { "file-scan-tasks": [...] } > > > *POST /v1/namespaces/ns/tables/t/scan *{ "filter": {"type": "in", "term": > "x", "values": [1, 2, 3] }, "select": ["x", "a.b"]} > > > { "file-scan-tasks": [...] } > > > > If this sounds good overall, we can update the prototype to have more > detailed discussions in code. > > > > -Jack > > > > > > > > > > > > On Thu, Dec 14, 2023 at 6:10 PM Ryan Blue <b...@tabular.io> wrote: > > The tasks might look something like this: > > > > CombinedPlanTask > > - List<ManifestPlanTask> > > > > ManifestPlanTask > > - int start > > - int length > > - ManifestFile dataManifest > > - List<ManifestFile> deleteManifests > > > > On Thu, Dec 14, 2023 at 4:07 PM Ryan Blue <b...@tabular.io> wrote: > > Seems like that track has expired (This Internet-Draft will expire on 13 > May 2022) > > Yeah, looks like we should just use POST. That’s too bad. QUERY seems like > a good idea to me. > > Distinguish planning using shard or not > > I think this was a mistake on my part. I was still thinking that we would > have a different endpoint for first-level planning to produce shards and > the route to actually get files. Since both are POST requests with the same > path (/v1/namespaces/ns/tables/t/scans) that no longer works. What about > /v1/namespaces/ns/tables/t/scan and /v1/namespaces/ns/tables/t/plan? The > latter could use some variant of planFiles since that’s what we are > wrapping in the Java API. > > Necessity of scan ID > > Yes, I agree. If you have shard IDs then you don’t really need a scan ID. > You could always have one internally but send it as part of the shard ID. > > Shape of shard payload > > I think we have 2 general options depending on how strict we want to be. > > 1. Require a standard shard definition > 2. Allow arbitrary JSON and leave it to the service > > I lean toward the first option, which would be a data manifest and the > associated delete manifests for the partition. We could also extend that to > a group of manifests, each with a list of delete manifests. And we could > also allow splitting to ensure tasks don’t get too large with big files. > This all looks basically like FileScanTask, but with manifests and delete > manifests. > > > > On Wed, Dec 13, 2023 at 4:39 PM Jack Ye <yezhao...@gmail.com> wrote: > > Seems like that track has expired (This Internet-Draft will expire on 13 > May 2022), not sure how these RFCs are managed, but it does not seem > hopeful to have this verb in. I think people are mostly using POST for this > use case already. > > > > But overall I think we are in agreement with the general direction. A few > detail discussions: > > > > *Distinguish planning using shard or not* > > Maybe we should add a query parameter like *distributed=true* to > distinguish your first and third case, since they are now sharing the same > signature. If the requester wants to use distributed planning, then some > sharding strategy is provided as a response for the requester to send more > detailed requests. > > *Necessity of scan ID* > In this approach, is scan ID still required? Because the shard payload > already fully describes the information to retrieve, it seems like we can > just drop the *scan-id* query parameter in the second case. Seems like > it's kept for the case if we still want to persist some state, but it seems > like we can make a stateless style fully working. > > *Shape of shard payload* > What do you think is necessary information of the shard payload? It seems > like we need at least the location of the manifests, plus the delete > manifests or delete files associated with the manifests. I like the idea of > making it a "shard task" that is similar to a file scan task, and it might > allow us to return a mixture of both types of tasks, so we can have better > control of the response size. > > -Jack > > > > On Wed, Dec 13, 2023 at 3:50 PM Ryan Blue <b...@tabular.io> wrote: > > I just changed it to POST after looking into support for the QUERY method. > It's a new HTTP method for cases like this where you don't want to pass > everything through query params. Here's the QUERY method RFC > <https://www.ietf.org/archive/id/draft-ietf-httpbis-safe-method-w-body-02.html>, > but I guess it isn't finalized yet? > > > > Just read them like you would a POST request that doesn't actually create > anything. > > > > On Wed, Dec 13, 2023 at 3:45 PM Jack Ye <yezhao...@gmail.com> wrote: > > Thanks, the Gist explains a lot of things. This is actually very close to > our way of implementing the shard ID, we were defining the shard ID as a > string, and the string content is actually something similar to the > information of the JSON payload you showed, so we can persist minimum > information in storage. > > > > Just one clarification needed for your Gist: > > > > > QUERY /v1/namespaces/ns/tables/t/scans?scan-id=1 > > > > > { "shard": { "id": 1, "manifests": ["C"] }, "filter": {"type": "in", > "term": "x", "values": [1, 2, 3] } } > > > > > > > > { "file-scan-tasks": [...] } > > > > Here, what does this QUERY verb mean? Is that a GET? If it's GET, we > cannot have a request body. That's actually why we expressed that as an ID > string, since we can put it as a query parameter. > > > > -Jack > > > > > > > > > > > > > > > > > > > > On Wed, Dec 13, 2023 at 3:25 PM Ryan Blue <b...@tabular.io> wrote: > > Jack, > > It sounds like what I’m proposing isn’t quite clear because your initial > response was arguing for a sharding capability. I agree that sharding is a > good idea. I’m less confident about two points: > > 1. Requiring that the service is stateful. As Renjie pointed out, that > makes it harder to scale the service. > 2. The need for both pagination *and* sharding as separate things > > And I also think that Fokko has a good point about trying to keep things > simple and not requiring the CreateScan endpoint. > > For the first point, I’m proposing that we still have a CreateScan > endpoint, but instead of sending only a list of shard IDs it can also send > either a standard shard “task” or an optional JSON definition. Let’s assume > we can send arbitrary JSON for an example. Say I have a table with 4 > manifests, A through D and that C and D match some query filter. When I > call the CreateScan endpoint, the service would send back tasks with that > information: {"id": 1, "manifests": ["C"]}, {"id": 2, "manifests": ["D"]}. > By sending what the shards mean (the manifests to read), my service can be > stateless: any node can get a request for shard 1, read manifest C, and > send back the resulting data files. > > I don’t see much of an argument against doing this *in principle*. It > gives you the flexibility to store state if you choose or to send state to > the client for it to pass back when calling the GetTasks endpoint. There > is a practical problem, which is that it’s annoying to send a GET request > with a JSON payload because you can’t send a request body. It’s probably > obvious, but I’m also not a REST purist so I’d be fine using POST or QUERY > for this. It would look something like this Gist > <https://gist.github.com/rdblue/d2b65bd2ad20f85ee9d04ccf19ac8aba>. > > In your last reply, you also asked whether a stateless service is a goal. > I don’t think that it is, but if we can make simple changes to the spec to > allow more flexibility on the server side, I think that’s a good direction. > You also asked about a reference implementation and I consider > CatalogHandlers > <https://github.com/apache/iceberg/blob/main/core/src/main/java/org/apache/iceberg/rest/CatalogHandlers.java> > to be that reference. It does everything except for the work done by your > choice of web application framework. It isn’t stateless, but it only relies > on a Catalog implementation for persistence. > > For the second point, I don’t understand why we need both sharding and > pagination. That is, if we have a protocol that allows sharding, why is > pagination also needed? From my naive perspective on how sharding would > work, we should be able to use metadata from the manifest list to limit the > potential number of data files in a given shard. As long as we can limit > the size of a shard to produce more, pagination seems like unnecessary > complication. > > Lastly, for Fokko’s point, I think another easy extension to the proposal > is to support a direct call to GetTasks. There’s a trade-off here, but if > you’re already sending the original filter along with the request (in order > to filter records from manifest C for instance) then the request is > already something the protocol can express. There’s an objection concerning > resource consumption on the service and creating responses that are too > large or take too long, but we can get around that by responding with a > code that instructs the client to use the CreateScan API like 413 > (Payload too large). I think that would allow simple clients to function > for all but really large tables. The gist above also shows what this might > look like. > > Ryan > > > > On Wed, Dec 13, 2023 at 11:53 AM Jack Ye <yezhao...@gmail.com> wrote: > > The current proposal definitely makes the server stateful. In our > prototype we used other components like DynamoDB to keep track of states. > If keeping it stateless is a tenant we can definitely make the proposal > closer to that direction. Maybe one thing to make sure is, is this a core > tenant of the REST spec? Today we do not even have an official reference > implementation of the REST server, I feel it is hard to say what are the > core tenants. Maybe we should create one? > > > > Pagination is a common issue in the REST spec. We also see similar > limitations with other APIs like GetTables, GetNamespaces. When a catalog > has many namespaces and tables it suffers from the same issue. It is also > not ideal for use cases like web browsers, since typically you display a > small page of results and do not need the full list immediately. So I feel > we cannot really avoid some state to be kept for those use cases. > > > > Chunked response might be a good way to work around it. We also thought > about using HTTP2. However, these options seem to be not very compatible > with OpenAPI. We can do some further research in this domain, would really > appreciate it if anyone has more insights and experience with OpenAPI that > can provide some suggestions. > > > > -Jack > > > > > > > > On Tue, Dec 12, 2023 at 6:21 PM Renjie Liu <liurenjie2...@gmail.com> > wrote: > > Hi, Rahi and Jack: > > Thanks for raising this. > > > > My question is that the pagination and sharding will make the rest server > stateful, e.g. a sequence of calls is required to go to the same server. In > this case, how do we ensure the scalability of the rest server? > > > > > > On Wed, Dec 13, 2023 at 4:09 AM Fokko Driesprong <fo...@apache.org> wrote: > > Hey Rahil and Jack, > > > > Thanks for bringing this up. Ryan and I also discussed this briefly in the > early days of PyIceberg and it would have helped a lot in the speed of > development. We went for the traditional approach because that would also > support all the other catalogs, but now that the REST catalog is taking > off, I think it still makes a lot of sense to get it in. > > > > I do share the concern raised Ryan around the concepts of shards and > pagination. For PyIceberg (but also for Go, Rust, and DuckDB) that are > living in a single process today the concept of shards doesn't add value. I > see your concern with long-running jobs, but for the non-distributed cases, > it will add additional complexity. > > > > Some suggestions that come to mind: > > - Stream the tasks directly back using a chunked response, reducing > the latency to the first task. This would also solve things with the > pagination. The only downside I can think of is having delete files where > you first need to make sure there are deletes relevant to the task, this > might increase latency to the first task. > - Making the sharding optional. If you want to shard you call the > CreateScan first and then call the GetScanTask with the IDs. If you don't > want to shard, you omit the shard parameter and fetch the tasks directly > (here we need also replace the scan string with the full > column/expression/snapshot-id etc). > > Looking forward to discussing this tomorrow in the community sync > <https://iceberg.apache.org/community/#iceberg-community-events>! > > > > Kind regards, > > Fokko > > > > > > > > Op ma 11 dec 2023 om 19:05 schreef Jack Ye <yezhao...@gmail.com>: > > Hi Ryan, thanks for the feedback! > > > > I was a part of this design discussion internally and can provide more > details. One reason for separating the CreateScan operation was to make the > API asynchronous and thus keep HTTP communications short. Consider the case > where we only have GetScanTasks API, and there is no shard specified. It > might take tens of seconds, or even minutes to read through all the > manifest list and manifests before being able to return anything. This > means the HTTP connection has to remain open during that period, which is > not really a good practice in general (consider connection failure, load > balancer and proxy load, etc.). And when we shift the API to asynchronous, > it basically becomes something like the proposal, where a stateful ID is > generated to be able to immediately return back to the client, and the > client get results by referencing the ID. So in our current prototype > implementation we are actually keeping this ID and the whole REST service > is stateful. > > > > There were some thoughts we had about the possibility to define a "shard > ID generator" protocol: basically the client agrees with the service a way > to deterministically generate shard IDs, and service uses it to create > shards. That sounds like what you are suggesting here, and it pushes the > responsibility to the client side to determine the parallelism. But in some > bad cases (e.g. there are many delete files and we need to read all those > in each shard to apply filters), it seems like there might still be the > long open connection issue above. What is your thought on that? > > > > -Jack > > > > On Sun, Dec 10, 2023 at 10:27 AM Ryan Blue <b...@tabular.io> wrote: > > Rahil, thanks for working on this. It has some really good ideas that we > hadn't considered before like a way for the service to plan how to break up > the work of scan planning. I really like that idea because it makes it much > easier for the service to keep memory consumption low across requests. > > > > My primary feedback is that I think it's a little too complicated (with > both sharding and pagination) and could be modified slightly so that the > service doesn't need to be stateful. If the service isn't necessarily > stateful then it should be easier to build implementations. > > > > To make it possible for the service to be stateless, I'm proposing that > rather than creating shard IDs that are tracked by the service, the > information for a shard can be sent to the client. My assumption here is > that most implementations would create shards by reading the manifest list, > filtering on partition ranges, and creating a shard for some reasonable > size of manifest content. For example, if a table has 100MB of metadata in > 25 manifests that are about 4 MB each, then it might create 9 shards with > 1-4 manifests each. The service could send those shards to the client as a > list of manifests to read and the client could send the shard information > back to the service to get the data files in each shard (along with the > original filter). > > > > There's a slight trade-off that the protocol needs to define how to break > the work into shards. I'm interested in hearing if that would work with how > you were planning on building the service on your end. Another option is to > let the service send back arbitrary JSON that would get returned for each > shard. Either way, I like that this would make it so the service doesn't > need to persist anything. We could also make it so that small tables don't > require multiple requests. For example, a client could call the route to > get file tasks with just a filter. > > > > What do you think? > > > > Ryan > > > > On Fri, Dec 8, 2023 at 10:41 AM Chertara, Rahil > <rcher...@amazon.com.invalid> wrote: > > Hi all, > > My name is Rahil Chertara, and I’m a part of the Iceberg team at Amazon > EMR and Athena. I’m reaching out to share a proposal for a new Scan API > that will be utilized by the RESTCatalog. The process for table scan > planning is currently done within client engines such as Apache Spark. By > moving scan functionality to the RESTCatalog, we can integrate Iceberg > table scans with external services, which can lead to several benefits. > > For example, we can leverage caching and indexes on the server side to > improve planning performance. Furthermore, by moving this scan logic to the > RESTCatalog, non-JVM engines can integrate more easily. This all can be > found in the detailed proposal below. Feel free to comment, and add your > suggestions . > > Detailed proposal: > https://docs.google.com/document/d/1FdjCnFZM1fNtgyb9-v9fU4FwOX4An-pqEwSaJe8RgUg/edit#heading=h.cftjlkb2wh4h > > Github POC: https://github.com/apache/iceberg/pull/9252 > > Regards, > > Rahil Chertara > Amazon EMR & Athena > rcher...@amazon.com > > > > > > > -- > > Ryan Blue > > Tabular > > > > > -- > > Ryan Blue > > Tabular > > > > > -- > > Ryan Blue > > Tabular > > > > > -- > > Ryan Blue > > Tabular > > > > > -- > > Ryan Blue > > Tabular > > -- Ryan Blue Tabular
