ianmcook commented on code in PR #43553: URL: https://github.com/apache/arrow/pull/43553#discussion_r1706056549
########## docs/source/format/CDataInterfaceStatistics.rst: ########## @@ -0,0 +1,192 @@ +.. 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. + +.. _c-data-interface-statistics: + +===================================================== +Passing statistics through the Arrow C data interface +===================================================== + +Rationale +========= + +Statistics are useful for fast query processing. Many query engines +use statistics to optimize their query plan. + +Apache Arrow format doesn't have statistics but other formats that can +be read as Apache Arrow data may have statistics. For example, Apache +Parquet C++ can read Apache Parquet file as Apache Arrow data and +Apache Parquet file may have statistics. + +One of the Arrow C data interface use cases is the following: + +1. Module A reads Apache Parquet file as Apache Arrow data +2. Module A passes the read Apache Arrow data to module B through the + Arrow C data interface +3. Module B processes the passed Apache Arrow data + +If module A can pass the statistics associated with the Apache Parquet +file to module B through the Arrow C data interface, module B can use +the statistics to optimize its query plan. + +Goals +----- + +* Provide the standard way to pass statistics through the Arrow C data + interface to avoid reinventing the wheel. +* The standard way must be easy to use with the Arrow C data interface. + +Non-goals +--------- + +* Provide a common way to pass statistics that can be used for + other interfaces such Arrow Flight too. + +For example, ADBC has the statistics related APIs. This specification +doesn't replace them. + +.. _c-data-interface-statistics-schema: + +Schema +====== + +This specification provides only the schema for statistics. Producers +passes statistics as a map Arrow array that uses the schema through +the Arrow C data interface. + +Here is the schema for a statistics map Arrow Array: + +.. list-table:: + :header-rows: 1 + + * - Key or items + - Data type + - Nullable + - Notes + * - key + - ``int32`` + - ``true`` + - The column index or null if the statistics refer to whole table + or record batch. + * - items + - ``map`` + - ``false`` + - Statistics for the target column, table or record batch. See + the separated table for details. Review Comment: ```suggestion the separate table below for details. ``` -- 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: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
