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Hi Huaxin, This is a really interesting and valuable proposal — it provides a great way to address the issue of duplicate client requests. Thank you for proposing and driving this forward! One point that isn’t entirely clear to me is how the server uniquely identifies each request. Are we relying solely on the idempotency-key being globally unique, or is there an additional identifier such as clientId + idempotency-key? Based on the current discussion, it sounds like the proposal expects the key itself to be globally unique, likely through the use of a UUID, but I’d like to double-check my understanding. If we are indeed relying on the client to generate a globally unique ID, that approach makes sense. However, it doesn’t seem necessary to mandate the use of UUIDs, as there are other valid methods for achieving global uniqueness. Imposing a further restriction to UUIDv7 would place additional constraints on the client implementation. >From a specification perspective, I think it would be better to separate the spec from the implementation. In other words, we should make it clear that the key must be globally unique, but we don’t need to specify that it must be a UUID or UUIDv7. Best Regards, Yun On Fri, Oct 24, 2025 at 4:41 PM huaxin gao <[email protected]> wrote: > > Hi all, > > Thank you for taking the time to review my proposal and PR—I really > appreciate the input. > > There’s one remaining issue I’d like to settle. In the Iceberg Catalog > Community sync, many preferred mandating UUIDv7 for the idempotency key. At > the same time, there are some concerns: > > If we need a timestamp, it should be a separate field; we shouldn’t use the > UUIDv7 timestamp. > > If we use the UUID timestamp for expiry, we’d have to require keys to be > generated at request time, which feels over-engineered. > > If we want to use the UUIDv7 timestamp, it should be for debugging only. > > Based on that, here’s a draft update to the spec: > > Key Requirements: > - Key format: UUIDv7 in string format as defined in RFC 9562. > See > https://datatracker.ietf.org/doc/html/rfc9562#name-example-of-a-uuidv7-value. > - The idempotency key must be globally unique (no reuse across different > operations). > - Catalogs SHOULD NOT expire keys before the end of the advertised token > lifetime. > - If Idempotency-Key is used, clients MUST reuse the same key when retrying > the same > logical operation and MUST generate a new key for a different operation. > - Server behavior: Servers MUST validate the syntactic validity of UUIDv7 > (per RFC 9562). > Servers MUST NOT make behavioral decisions based on the UUID’s internal > timestamp fields. > The idempotency key is an opaque, unique identifier used only for > lookup/deduplication. > > This reads a bit awkward to me: we mandate UUIDv7 but prohibit using its > timestamp, which seems to undercut the reason to require v7 in the first > place. > > I’d appreciate feedback on whether we should: > > Option 1 — Require v7. > Keep UUIDv7 required, with the server restrictions above (syntactic v7 > validation only; no behavioral decisions based on the embedded timestamp). > > Option 2 — Version-agnostic. > Make the client spec version-agnostic (require RFC 9562 UUID textual form; > allow v7 as a recommendation). Leave any timestamp/lifetime mechanics to a > server-side (Polaris idempotency) document. > > Thanks again for the thoughtful discussion. > > Best, > > Huaxin > > > On Mon, Sep 29, 2025 at 5:47 PM Dmitri Bourlatchkov <[email protected]> wrote: >> >> Hi Huaxin, >> >> Sorry about the delay. I posted some comments on >> https://github.com/apache/iceberg/pull/14196 Some of them I might have >> mentioned on the doc too, so apologies if they got answered in the doc and I >> missed it. >> >> Cheers, >> Dmitri. >> >> On Thu, Sep 25, 2025 at 12:27 PM huaxin gao <[email protected]> wrote: >>> >>> Thank you all for taking the time to review and discuss! I’ve responded to >>> all questions and updated the proposal. If there are no additional >>> concerns, I’ll proceed to start a VOTE thread. >>> >>> Thanks, >>> Huaxin >>> >>> On Mon, Sep 22, 2025 at 1:30 AM Maninder Parmar >>> <[email protected]> wrote: >>>> >>>> +1, for low level retry which ensures that the idempotent key is never >>>> committed twice. I also agree that canonicalizing the request body where >>>> the client can change it due to conflict resolution and retry would be >>>> hard to get right. >>>> >>>> On Sat, Sep 20, 2025 at 5:58 AM Dennis Huo <[email protected]> wrote: >>>>> >>>>> +1 to this being mostly targeting a "low-level" retry semantic. Expanding >>>>> on that though I'd say even "client-side retries" really have two >>>>> distinct flavors: >>>>> >>>>> A. Business-logic-agnostic retries, e.g. in a common low-level HTTP >>>>> client library - behaviorally, these should behave largely the same as >>>>> "network infra retries". The key distinction is that in this case any >>>>> content hashing would be *post* serialization and even agnostic to >>>>> request-body content-type (i.e. not JSON-specific). >>>>> B. Application-specific retries, such as when Iceberg client will >>>>> potentially rebase on a new snapshot >>>>> >>>>> I think this aligns with what Peter and others mentioned earlier where >>>>> trying to canonicalize the *semantic* content of a request is probably >>>>> brittle/risky. And as Yufei mentions, case 2.B (client-side real >>>>> application-layer retries) should be using a new idempotency-key if it's >>>>> ever doing the retry at the later that requires re-serializating JSON. >>>>> >>>>> Overall though I agree making the content-hash checking optional is a >>>>> good idea. >>>>> >>>>> On Fri, Sep 19, 2025 at 4:33 PM huaxin gao <[email protected]> wrote: >>>>>> >>>>>> Thanks, Peter and Yufei. I agree the main use case is >>>>>> network‑infrastructure retries. To keep the specification simple and >>>>>> move the proposal forward, let’s make the baseline key‑only idempotency. >>>>>> If there’s demand, we can add an optional payload‑binding mode >>>>>> (canonical JSON + SHA‑256), advertised via /v1/config. >>>>>> >>>>>> Thanks, >>>>>> >>>>>> Huaxin >>>>>> >>>>>> >>>>>> On Fri, Sep 19, 2025 at 1:31 PM Yufei Gu <[email protected]> wrote: >>>>>>> >>>>>>> "Network infrastructure retries" would be the dominant use case. I'd >>>>>>> NOT recommend clients retry with the same idempotency key if it >>>>>>> regenerated the request, instead, clients should reload before retry in >>>>>>> that case. >>>>>>> >>>>>>> Yufei >>>>>>> >>>>>>> >>>>>>> On Fri, Sep 19, 2025 at 2:05 AM Péter Váry >>>>>>> <[email protected]> wrote: >>>>>>>> >>>>>>>> Hi Huaxin, >>>>>>>> >>>>>>>> Could you clarify the specific use cases we intend to support >>>>>>>> regarding retry checking? Here are a couple of possibilities I had in >>>>>>>> mind: >>>>>>>> >>>>>>>> Network infrastructure retries – where the exact same request is >>>>>>>> retried. >>>>>>>> Client-side retries – where the client regenerates the request using >>>>>>>> the same program logic, resulting in identical content. >>>>>>>> >>>>>>>> If there are no security or other concerns, I’d suggest keeping the >>>>>>>> specification simple and avoiding mechanisms that surface client-side >>>>>>>> implementation errors. The cleanest approach might be to ignore the >>>>>>>> request content and rely solely on a user-provided key. >>>>>>>> >>>>>>>> Alternatively, we could include an optional error code in the >>>>>>>> response, which implementations may use to signal conflicts. The >>>>>>>> actual conflict detection logic can be left to the implementations—we >>>>>>>> don’t need to define it in the specification. If we go this route, we >>>>>>>> should also offer a way to disable these checks, since there will >>>>>>>> inevitably be cases where semantically identical requests are >>>>>>>> incorrectly flagged as conflicting. >>>>>>>> >>>>>>>> Thanks, >>>>>>>> Peter >>>>>>>> >>>>>>>> huaxin gao <[email protected]> ezt írta (időpont: 2025. szept. >>>>>>>> 19., P, 1:38): >>>>>>>>> >>>>>>>>> Thanks Steven for the +1 and for raising the fingerprint question! >>>>>>>>> Great points! >>>>>>>>> >>>>>>>>> What we need to protect against: >>>>>>>>> >>>>>>>>> Same logical request, different bytes across retries (pretty vs >>>>>>>>> compact JSON, map key order, ...). >>>>>>>>> Accidental key reuse with a changed payload. >>>>>>>>> >>>>>>>>> Options and tradeoffs: >>>>>>>>> >>>>>>>>> Exact byte checksum (e.g., SHA‑256 over raw body) >>>>>>>>> >>>>>>>>> Pro: trivial, fast >>>>>>>>> Con: too strict; benign diffs cause false mismatches >>>>>>>>> >>>>>>>>> Canonical JSON over full request, then hash (proposed) >>>>>>>>> >>>>>>>>> Pro: stable across whitespace/key order; simple to implement for >>>>>>>>> typed payloads >>>>>>>>> Con: slightly more work than raw checksum; >>>>>>>>> >>>>>>>>> Checksum of selected fields / field-by-field match >>>>>>>>> >>>>>>>>> Pro: can be faster for huge payloads; can ignore noisy fields >>>>>>>>> Con: could misses legitimate differences >>>>>>>>> >>>>>>>>> Request digest/signature >>>>>>>>> >>>>>>>>> Pro: very strong >>>>>>>>> Con: heavyweight >>>>>>>>> >>>>>>>>> Maybe we could make this configurable: >>>>>>>>> >>>>>>>>> canonical-json-sha256 (default) >>>>>>>>> raw-bytes-sha256 (strict) >>>>>>>>> trust-client-key (no fingerprint check) >>>>>>>>> >>>>>>>>> On the IETF draft status: >>>>>>>>> >>>>>>>>> I have also noted the draft’s expiry. We will align with its >>>>>>>>> semantics for now and can adjust if a new version lands. >>>>>>>>> >>>>>>>>> Thanks, >>>>>>>>> >>>>>>>>> Huaxin >>>>>>>>> >>>>>>>>> >>>>>>>>> On Thu, Sep 18, 2025 at 4:01 PM Steven Wu <[email protected]> >>>>>>>>> wrote: >>>>>>>>>> >>>>>>>>>> +1 for the feature that can make retry safe for 500s and improve the >>>>>>>>>> client fault-tolerance of transient server failures. >>>>>>>>>> >>>>>>>>>> Peter and Dimitri raised a good question on the fingerprint. The >>>>>>>>>> IETF draft doesn't actually define the fingerprint algo. We can also >>>>>>>>>> go with simple checksum of the entire request payload, which would >>>>>>>>>> be cheap to compute. Do we anticipate any anticipated scenarios >>>>>>>>>> where clients may rewrite the payload in different forms of >>>>>>>>>> serialized bytes during retries? >>>>>>>>>> >>>>>>>>>> * Checksum of the entire request payload. >>>>>>>>>> * Checksum of selected element(s) in the request payload. >>>>>>>>>> * Field value match for each field in the request payload. >>>>>>>>>> * Field value match for selected element(s) in the request >>>>>>>>>> payload. >>>>>>>>>> * Request digest/signature >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> BTW, the IETF draft seems to have expired without approval >>>>>>>>>> https://datatracker.ietf.org/doc/draft-ietf-httpapi-idempotency-key-header/ >>>>>>>>>> >>>>>>>>>> On Thu, Sep 18, 2025 at 3:46 PM huaxin gao <[email protected]> >>>>>>>>>> wrote: >>>>>>>>>>> >>>>>>>>>>> Thanks Peter and Dmitri for the thoughtful feedback! I really >>>>>>>>>>> appreciate you taking a close look at my proposal. I agree that >>>>>>>>>>> "semantic equality" is tricky, that's why the scope here is >>>>>>>>>>> intentionally narrow. >>>>>>>>>>> >>>>>>>>>>> Just to clarify scope: I’m not trying to solve general semantic >>>>>>>>>>> equivalence. For these specific, typed request payloads, I >>>>>>>>>>> serialize to a deterministic JSON and hash it. That normalizes >>>>>>>>>>> benign diffs (map order, whitespace) without trying to infer >>>>>>>>>>> meaning. The goal is a stable fingerprint so that if a key is >>>>>>>>>>> accidentally reused with a changed payload, we surface that instead >>>>>>>>>>> of silently diverging. >>>>>>>>>>> >>>>>>>>>>> To make this feel less brittle, I’ll add tests for the practical >>>>>>>>>>> cases (ordering/whitespace, nested maps, a clear null‑vs‑missing >>>>>>>>>>> rule, numeric formatting), plus end‑to‑end tests in the in‑memory >>>>>>>>>>> REST fixture with failure injection (in‑flight dup, finalize >>>>>>>>>>> failure -> reconcile, etc.). Happy to walk through these if helpful. >>>>>>>>>>> >>>>>>>>>>> I’m also open to adding a config switch for “trust‑client‑key only” >>>>>>>>>>> if that’s preferred in some environments. My intent is to stay >>>>>>>>>>> aligned with the IETF Idempotency‑Key guidance (first request wins; >>>>>>>>>>> conflicting reuse is rejected, and reusing a key with a different >>>>>>>>>>> request payload is rejected via an idempotency fingerprint) while >>>>>>>>>>> keeping things as simple as possible and protecting us from >>>>>>>>>>> accidental key misuse. Would love to align on the lightest approach >>>>>>>>>>> that meets those goals. >>>>>>>>>>> >>>>>>>>>>> Thanks, >>>>>>>>>>> >>>>>>>>>>> Huaxin >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> On Thu, Sep 18, 2025 at 6:17 AM Dmitri Bourlatchkov >>>>>>>>>>> <[email protected]> wrote: >>>>>>>>>>>> >>>>>>>>>>>> Hi All, >>>>>>>>>>>> >>>>>>>>>>>> I agree that checking request contents is almost redundant in this >>>>>>>>>>>> case. >>>>>>>>>>>> >>>>>>>>>>>> If the randomness quality of Idempotency-Key value is good, >>>>>>>>>>>> collisions are very unlikely on the server side. Given that, any >>>>>>>>>>>> content checks the server performs are essentially validating that >>>>>>>>>>>> clients correctly reuse the generated Idempotency-Key value. (this >>>>>>>>>>>> is mostly the same as my comment on the related Polaris >>>>>>>>>>>> discussion). >>>>>>>>>>>> >>>>>>>>>>>> I'd like to propose making the content check optional so that >>>>>>>>>>>> servers may or may not implement it according to their design >>>>>>>>>>>> principles and constraints and emphasizing that clients should use >>>>>>>>>>>> unique keys (e.g. UUIDs)... basically going with option 2 from >>>>>>>>>>>> Peter's email. >>>>>>>>>>>> >>>>>>>>>>>> I believe this is in line with the SHOULD word used for this case >>>>>>>>>>>> in the IETF draft [1] (section 2.7). >>>>>>>>>>>> >>>>>>>>>>>> [1] >>>>>>>>>>>> https://datatracker.ietf.org/doc/html/draft-ietf-httpapi-idempotency-key-header-06 >>>>>>>>>>>> >>>>>>>>>>>> Thanks, >>>>>>>>>>>> Dmitri. >>>>>>>>>>>> >>>>>>>>>>>> On Thu, Sep 18, 2025 at 7:56 AM Péter Váry >>>>>>>>>>>> <[email protected]> wrote: >>>>>>>>>>>>> >>>>>>>>>>>>> Thanks Huaxin for the proposal, and sorry for the late review - I >>>>>>>>>>>>> had a bit of a busy week. >>>>>>>>>>>>> I have one main question, which I have also added as a comment to >>>>>>>>>>>>> the doc: >>>>>>>>>>>>> - Why do we try to compare the request contents when the >>>>>>>>>>>>> Idempotency-Key is the same for the requests? The comparison >>>>>>>>>>>>> algorithm is a bit complicated, and seems brittle to me. >>>>>>>>>>>>> Consistent field ordering, maps, and maybe even inconsistency in >>>>>>>>>>>>> upper case/lower case letters might mean technically the same >>>>>>>>>>>>> request. >>>>>>>>>>>>> >>>>>>>>>>>>> In my previous roles (admittedly more than 10 years ago) I was >>>>>>>>>>>>> extensively working on APIs like this, and we have never really >>>>>>>>>>>>> succeeded in creating a good enough "are these 2 requests are >>>>>>>>>>>>> really the same semantically" checks. >>>>>>>>>>>>> >>>>>>>>>>>>> I would simplify these requirements, unless there are serious >>>>>>>>>>>>> arguments for the existence of these checks: >>>>>>>>>>>>> >>>>>>>>>>>>> Either check for exact matches - without any magic - this could >>>>>>>>>>>>> be used for detecting issues where the duplication happens on the >>>>>>>>>>>>> network side, or >>>>>>>>>>>>> Rely entirely on the clients to provide the correct >>>>>>>>>>>>> Idempotency-Key. >>>>>>>>>>>>> >>>>>>>>>>>>> I would prefer the 2nd. >>>>>>>>>>>>> Otherwise I agree with the contents of the proposal. It is nicely >>>>>>>>>>>>> done! (edited) >>>>>>>>>>>>> >>>>>>>>>>>>> Yufei Gu <[email protected]> ezt írta (időpont: 2025. szept. >>>>>>>>>>>>> 18., Cs, 2:54): >>>>>>>>>>>>>> >>>>>>>>>>>>>> Thanks for the proposal. It's a nice feature to make retry more >>>>>>>>>>>>>> reliable and efficient. Left some comments. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Yufei >>>>>>>>>>>>>> >>>>>>>>>>>>>> >>>>>>>>>>>>>> On Mon, Sep 15, 2025 at 3:53 PM Kevin Liu >>>>>>>>>>>>>> <[email protected]> wrote: >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Thanks for writing up the proposal! Makes sense to add >>>>>>>>>>>>>>> idempotency to mutation requests. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> It would be helpful to add this feature to both the catalog >>>>>>>>>>>>>>> test framework and the iceberg-rest-fixture. The latter is used >>>>>>>>>>>>>>> by the subprojects for testing and would come in handy when we >>>>>>>>>>>>>>> want to test out the client implementation. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> For other reviewers, the Stripe documentation on idempotency >>>>>>>>>>>>>>> was a helpful read, >>>>>>>>>>>>>>> https://docs.stripe.com/api/idempotent_requests. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Best, >>>>>>>>>>>>>>> Kevin Liu >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> On Mon, Sep 15, 2025 at 11:38 AM Szehon Ho >>>>>>>>>>>>>>> <[email protected]> wrote: >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Hi, >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Sounds like fairly standard practice and makes sense to me in >>>>>>>>>>>>>>>> the first read. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Thanks, >>>>>>>>>>>>>>>> Szehon >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> On Mon, Sep 15, 2025 at 10:09 AM Russell Spitzer >>>>>>>>>>>>>>>> <[email protected]> wrote: >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> I think based on the feedback on the proposal and in recent >>>>>>>>>>>>>>>>> syncs we should probably move forward with the actual Spec >>>>>>>>>>>>>>>>> Change PR so we can see what this looks like and move on to a >>>>>>>>>>>>>>>>> discussion of how the Catalog test framework should test this. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> On 2025/08/22 18:26:23 huaxin gao wrote: >>>>>>>>>>>>>>>>> > Hi all, >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> > I’d like to propose a change to Iceberg’s REST API to make >>>>>>>>>>>>>>>>> > mutation >>>>>>>>>>>>>>>>> > requests safely retryable. >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> > *The Problem* >>>>>>>>>>>>>>>>> > If a POST mutation (e.g., updateTable) succeeds in the >>>>>>>>>>>>>>>>> > catalog but the >>>>>>>>>>>>>>>>> > client doesn’t receive the response (timeout, connection >>>>>>>>>>>>>>>>> > closed, etc.), a >>>>>>>>>>>>>>>>> > second attempt can hit 409 Conflict. The client interprets >>>>>>>>>>>>>>>>> > the 409 as a >>>>>>>>>>>>>>>>> > failed commit and deletes the associated metadata files, >>>>>>>>>>>>>>>>> > causing >>>>>>>>>>>>>>>>> > catalog/storage inconsistency. >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> > *The Proposed Solution* >>>>>>>>>>>>>>>>> > Introduces an optional Idempotency-Key HTTP header on REST >>>>>>>>>>>>>>>>> > mutation >>>>>>>>>>>>>>>>> > endpoints and has the Iceberg client pass it through. >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> > *Semantics *(first processed request wins): >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> > - >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> > Same key + same canonical payload -> return the original >>>>>>>>>>>>>>>>> > result (no >>>>>>>>>>>>>>>>> > re-execution). >>>>>>>>>>>>>>>>> > - >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> > Same key + different payload -> 422 (Unprocessable >>>>>>>>>>>>>>>>> > Content). >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> > *Capability discovery:* catalogs can advertise support and >>>>>>>>>>>>>>>>> > retention so >>>>>>>>>>>>>>>>> > clients know when a retry is safe, e.g. >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> > { >>>>>>>>>>>>>>>>> > "idempotency-tokens-respected": true, >>>>>>>>>>>>>>>>> > "idempotency-token-lifetime": "30m" } >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> > *Scope in Iceberg:* update the OpenAPI to include the >>>>>>>>>>>>>>>>> > header, and add >>>>>>>>>>>>>>>>> > client pass-through + honoring capability discovery. No >>>>>>>>>>>>>>>>> > server >>>>>>>>>>>>>>>>> > implementation is mandated—catalogs (e.g., Polaris) can >>>>>>>>>>>>>>>>> > implement >>>>>>>>>>>>>>>>> > storage/TTL/replay as they choose. >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> > *Standards alignment:* uses the industry-standard header >>>>>>>>>>>>>>>>> > name and matches >>>>>>>>>>>>>>>>> > the IETF HTTPAPI Idempotency-Key draft >>>>>>>>>>>>>>>>> > <https://datatracker.ietf.org/doc/html/draft-ietf-httpapi-idempotency-key-header> >>>>>>>>>>>>>>>>> > semantics. >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> > *Compatibility:* fully backward compatible. Servers that >>>>>>>>>>>>>>>>> > don’t support it >>>>>>>>>>>>>>>>> > can ignore the header; clients can detect support via >>>>>>>>>>>>>>>>> > capability discovery. >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> > Here is the proposal >>>>>>>>>>>>>>>>> > <https://docs.google.com/document/d/1WyiIk08JRe8AjWh63txIP4i2xcIUHYQWFrF_1CCS3uw/edit?tab=t.0>. >>>>>>>>>>>>>>>>> > Looking forward to your thoughts. >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> > Thanks, >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> > Huaxin >>>>>>>>>>>>>>>>> >
