huaxingao commented on code in PR #16961: URL: https://github.com/apache/iceberg/pull/16961#discussion_r3486524548
########## format/index.md: ########## @@ -0,0 +1,322 @@ +--- +title: "Index 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 Index Specification + +## Background and Motivation + +Indexes enable query engines to locate relevant rows without scanning entire datasets. +They can accelerate point lookups, range predicates, and other retrieval patterns +while preserving Iceberg's table format, snapshot isolation, and interoperability. + +This specification defines: + +- A portable metadata format for indexes +- A catalog-managed index object independent from table metadata +- A common storage architecture for index data +- A framework for defining new index types and transform functions + +Indexes are optional. Engines may choose to create, maintain, consume, or ignore them. + +## Goals + +- Define a common metadata format for indexes +- Allow indexes to evolve independently from table metadata +- Enable index sharing across engines +- Provide a foundation for future index types + +## Definitions + +### Index Type + +The index type defines the logical category of an index and the class of queries it is designed to accelerate. + +The following index type is defined in this specification: + +| Type | +|--------| +| SCALAR | + +The following index types are reserved for future specifications: + +| Type | +|--------| +| VECTOR | +| TERM | + +The index type communicates the capabilities of an index to query engines and helps determine whether an index is +applicable to a particular query. + +### Index Transform Function + +The index transform function defines how the index organization key is derived from source table columns when rows are +stored in the index. + +The transform function determines the physical organization of the indexed data and therefore influences which query +patterns can efficiently leverage the index. + +The following index types are reserved for future specifications: + +| Transform | +|-----------| +| IDENTITY | +| HASH | +| HILBERT | + +The following transform functions are reserved for future specifications: + +| Transform | +|-----------| +| IVF | + +Index Instances may share the same index type while using different transform functions. + +### Index Instance + +An index instance is a concrete realization of an index type and function applied to a specific table. + +Users create index instances by specifying: + +- The source table +- The index type +- The transform function +- The indexed columns +- The included columns +- Index properties + +Multiple instances of the same index type may exist for a table. + +### Index Snapshot + +An index snapshot is an immutable version of the index data generated from a specific table snapshot. + +Each index snapshot references a complete set of index files and contains all data from the referenced table snapshot. + +## Overview + +Indexes are stored as independent catalog objects. + +Like Iceberg tables, views, and functions: + +- Metadata and data files are immutable +- Updates create new metadata files +- Catalogs perform atomic metadata swaps + +Index data is stored separately from metadata. + +Each index snapshot references a tracking file which describes the leaf files belonging to the snapshot. + +```text +Index Metadata + | + +-- Index Snapshot + | + +-- Tracking File + | + +-- Leaf Data Files +``` + +Transform functions derive a transform value from the key columns and determine how index entries are organized within +the leaf files. +- The transform value space is divided into non-overlapping ranges. +- Each leaf file stores entries for a single range. +- The tracking file stores range bounds for each leaf file. + +This structure enables efficient planning while keeping the data layout flexible for different index implementations. + +## Index Metadata + +The index metadata file stores the index definition and snapshot history. + +### Index Metadata File + +| Requirement | Field | Type | Description | +|-------------|---------------------|--------------------------|-------------------------------------------------| +| required | format-version | int | Index specification version | +| required | uuid | string | Stable UUID assigned at creation | +| required | table-uuid | string | UUID of the indexed table | +| required | location | string | Index root location | +| required | type | string | Logical index type | +| required | transform-function | string | Physical organization transform | +| required | key-column-ids | list<int> | Indexed columns | +| optional | included-column-ids | list<int> | Included columns | +| required | file-format | string | Leaf file format | +| optional | properties | map<string,string> | Index properties applicable for every snapshot | +| required | snapshots | list<index-snapshot> | Known index snapshots | + +## Index Snapshot + +Each index snapshot corresponds to one version of the index data. + +| Requirement | Field | Type | Description | +|-------------|--------------------------|--------------------|---------------------------------------------------------------------| +| required | snapshot-id | long | Index snapshot identifier | +| required | source-table-snapshot-id | long | Source table snapshot | +| required | timestamp-ms | long | Snapshot creation timestamp | +| required | tracking-file | string | Tracking file location | +| optional | properties | map<string,string> | Snapshot properties specific to this snapshot | +| optional | key_metadata | binary | Implementation-specific key metadata, for tracking file encryption. | + +## Tracking File + +Each index snapshot references exactly one tracking file. + +It contains summary metadata about all leaf files belonging to the index snapshot and enables efficient planning +without scanning every leaf file. + +The tracking file may be stored using any supported metadata file format. + +### Tracking File Entry + +Each entry describes a single leaf file. + +### Tracking File Entry + +Each tracking file contains a collection of tracking file entries. A tracking file entry describes a single leaf file +tracked by an index snapshot. The fields are the subset of the V4 manifest entry fields that are relevant to planning +queries against the index. +Entries contain aggregated statistics for all referenced leaf files, enabling engines to perform pruning and planning +without opening every leaf file. + +| Field ID | Name | Type | Requirement | Description | +|----------|--------------------|---------|--------------|--------------------------------------------------------------------------------------------------------------| +| 100 | location | string | required | Location of the referenced file. | +| 101 | file_format | string | required | File format name, such as parquet, avro, or orc. | +| 103 | record_count | long | required | Number of records contained in the referenced file or aggregated under the referenced tracking file. | +| 104 | file_size_in_bytes | long | required | Total file size in bytes. | +| 146 | content_stats | struct | optional | Statistics used for planning and pruning, including transform-key statistics and optional column statistics. | +| 131 | key_metadata | binary | optional | Implementation-specific key metadata, used for leaf file encryption. | Review Comment: `key_metadata` -> `key-metadata`? -- This is an automated message from the Apache Git Service. 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