flyrain commented on code in PR #14117: URL: https://github.com/apache/iceberg/pull/14117#discussion_r2373180339
########## format/udf-spec.md: ########## @@ -0,0 +1,221 @@ +--- +title: "SQL UDF Spec" +--- +<!-- + - Licensed to the Apache Software Foundation (ASF) under one or more + - contributor license agreements. See the NOTICE file distributed with + - this work for additional information regarding copyright ownership. + - The ASF licenses this file to You under the Apache License, Version 2.0 + - (the "License"); you may not use this file except in compliance with + - the License. You may obtain a copy of the License at + - + - http://www.apache.org/licenses/LICENSE-2.0 + - + - Unless required by applicable law or agreed to in writing, software + - distributed under the License is distributed on an "AS IS" BASIS, + - WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + - See the License for the specific language governing permissions and + - limitations under the License. + --> + +# Iceberg SQL UDF Spec + +## Background and Motivation + +A SQL user-defined function (UDF or UDTF) is a callable routine that accepts input parameters, executes a function body, +and returns either: + +* **Scalar functions (UDFs):** return a single value. +* **Table functions (UDTFs):** return a table with one or more rows and columns. + +Most compute engines (e.g., Spark, Trino) already support UDFs, but in different and incompatible ways. Without a common +standard, UDFs cannot be reliably shared across engines or reused in multi-engine environments. + +This specification introduces a standardized metadata format for UDFs in Iceberg. + +## Goals + +* Define a portable metadata format for both scalar and table SQL UDFs. The metadata is self-contained and can be moved across catalogs. +* Support function evolution through versioning and rollback. +* Provide consistent semantics for representing UDFs across engines. + +## Overview + +UDF metadata follows the same design principles as Iceberg table and view metadata: each function is represented by a +**self-contained metadata file**. Metadata captures definitions, parameters, return types, documentation, security, +properties, and engine-specific representations. + +* Any modification (new overload, updated representation, changed properties, etc.) creates a new metadata file. The old file is replaced atomically. +* Each metadata file includes recent definition versions, enabling rollbacks without external state. + +## Specification + +### UDF Metadata +The UDF metadata file has the following fields: + +| Requirement | Field name | Description | +|-------------|------------------------------|------------------------------------------------------------------| +| *required* | `function-uuid` | A UUID that identifies the function, generated once at creation. | +| *required* | `format-version` | Metadata format version (must be `1`). | +| *required* | `definition` | List of function overloads. | +| *required* | `definition-versions` | List of versioned function definitions. | +| *required* | `current-definition-version` | Identifier of the current definition version. | +| *optional* | `location` | The storage location of metadata files. | +| *optional* | `properties` | Arbitrary key-value pairs. | +| *optional* | `secure` | Whether it is a secure function. Default: `false`. | +| *optional* | `doc` | Documentation string. | + +### Overload + +Function overloads allow multiple implementations of the same function name with different signatures. Each overload has +the following fields: + +| Requirement | Field name | Description | +|-------------|-----------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| +| *required* | `overload-uuid` | A UUID that identifies this function overload. | +| *required* | `parameters` | Ordered list of function parameter definitions (name, type, optional doc). The order of parameters in this list **must exactly match** the order of arguments provided when invoking the function. | +| *required* | `return-type` | Return type (scalar or struct). Example: `"string"` or `"struct<...>"` | Review Comment: I think struct is fine. For UDF, I think it's OK to support all Iceberg type. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: issues-unsubscr...@iceberg.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: issues-unsubscr...@iceberg.apache.org For additional commands, e-mail: issues-h...@iceberg.apache.org
