lxy-9602 commented on code in PR #6881: URL: https://github.com/apache/paimon/pull/6881#discussion_r2645229868
########## docs/content/program-api/cpp-api.md: ########## @@ -0,0 +1,259 @@ +--- +title: "Cpp API" +weight: 5 +type: docs +aliases: + - /api/cpp-api.html +--- + +<!-- +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. +--> + +# Cpp API + +Paimon C++ is a high-performance C++ implementation of Apache Paimon. Paimon C++ aims to provide a native, +high-performance and extensible implementation that allows native engines to access the Paimon datalake +format with maximum efficiency. + +## Environment Settings + +[Paimon C++](https://github.com/alibaba/paimon-cpp.git) is currently governed under Alibaba open source +community.You can checkout the [document](https://alibaba.github.io/paimon-cpp/getting_started.html) +for more details about envinroment settings. + +``` +git clone https://github.com/alibaba/paimon-cpp.git +cd paimon-cpp +mkdir build-release +cd build-release +cmake .. +make -j8 # if you have 8 CPU cores, otherwise adjust +make install +``` + +## Create Catalog + +Before coming into contact with the Table, you need to create a Catalog. + +```c++ +#include "paimon/catalog/catalog.h" + +// Note that keys and values are all string +std::map<std::string, std::string> options; +PAIMON_ASSIGN_OR_RAISE(std::unique_ptr<paimon::Catalog> catalog, + paimon::Catalog::Create(root_path, options)); +``` + +Current C++ Paimon only supports filesystem catalog. In the future, we will support REST catalog. +See [Catalog]({{< ref "concepts/catalog" >}}). + +You can use the catalog to create table for writing data. + +## Create Database + +Table is located in a database. If you want to create table in a new database, you should create it. + +```c++ +PAIMON_RETURN_NOT_OK(catalog->CreateDatabase('database_name', options, /*ignore_if_exists=*/false)); +``` + +## Create Table + +Table schema contains fields definition, partition keys, primary keys, table options +The field definition is described by `Arrow::Schema`. All arguments except fields definition are optional. + +for example: + +```c++ +arrow::FieldVector fields = { + arrow::field("f0", arrow::utf8()), + arrow::field("f1", arrow::int32()), + arrow::field("f2", arrow::int32()), + arrow::field("f3", arrow::float64()), +}; +std::shared_ptr<arrow::Schema> schema = arrow::schema(fields); +::ArrowSchema arrow_schema; +arrow::Status arrow_status = arrow::ExportSchema(*schema, &arrow_schema); +if (!arrow_status.ok()) { + return paimon::Status::Invalid(arrow_status.message()); +} +PAIMON_RETURN_NOT_OK(catalog->CreateTable(paimon::Identifier(db_name, table_name), + &arrow_schema, + /*partition_keys=*/{}, + /*primary_keys=*/{}, options, + /*ignore_if_exists=*/false)); +``` + +See [Data Types](https://alibaba.github.io/paimon-cpp/user_guide/data_types.html) for all supported +`arrow-to-paimon` data types mapping. + +## Batch Write + +Paimon table write is Two-Phase Commit, you can write many times, but once committed, no more data can be written. +C++ Paimon uses Apache Arrow as [in-memory format], check out [document](https://alibaba.github.io/paimon-cpp/user_guide/arrow.html) +for more details. + +for example: +```c++ +arrow::Result<std::shared_ptr<arrow::StructArray>> PrepareData(const arrow::FieldVector& fields) { + arrow::StringBuilder f0_builder; + arrow::Int32Builder f1_builder; + arrow::Int32Builder f2_builder; + arrow::DoubleBuilder f3_builder; + + std::vector<std::tuple<std::string, int, int, double>> data = { + {"Alice", 1, 0, 11.0}, {"Bob", 1, 1, 12.1}, {"Cathy", 1, 2, 13.2}}; + + for (const auto& row : data) { + ARROW_RETURN_NOT_OK(f0_builder.Append(std::get<0>(row))); + ARROW_RETURN_NOT_OK(f1_builder.Append(std::get<1>(row))); + ARROW_RETURN_NOT_OK(f2_builder.Append(std::get<2>(row))); + ARROW_RETURN_NOT_OK(f3_builder.Append(std::get<3>(row))); + } + + std::shared_ptr<arrow::Array> f0_array, f1_array, f2_array, f3_array; + ARROW_RETURN_NOT_OK(f0_builder.Finish(&f0_array)); + ARROW_RETURN_NOT_OK(f1_builder.Finish(&f1_array)); + ARROW_RETURN_NOT_OK(f2_builder.Finish(&f2_array)); + ARROW_RETURN_NOT_OK(f3_builder.Finish(&f3_array)); + + std::vector<std::shared_ptr<arrow::Array>> children = {f0_array, f1_array, f2_array, f3_array}; + auto struct_type = arrow::struct_(fields); + return std::make_shared<arrow::StructArray>(struct_type, f0_array->length(), children); +} +``` + +```c++ +std::string table_path = root_path + "/" + db_name + ".db/" + table_name; +std::string commit_user = "some_commit_user"; +// write +paimon::WriteContextBuilder context_builder(table_path, commit_user); +PAIMON_ASSIGN_OR_RAISE(std::unique_ptr<paimon::WriteContext> write_context, + context_builder.SetOptions(options).Finish()); +PAIMON_ASSIGN_OR_RAISE(std::unique_ptr<paimon::FileStoreWrite> writer, + paimon::FileStoreWrite::Create(std::move(write_context))); +// prepare data +auto struct_array = PrepareData(fields); +if (!struct_array.ok()) { + return paimon::Status::Invalid(struct_array.status().ToString()); +} +::ArrowArray arrow_array; +arrow_status = arrow::ExportArray(*struct_array.ValueUnsafe(), &arrow_array); +if (!arrow_status.ok()) { + return paimon::Status::Invalid(arrow_status.message()); +} +paimon::RecordBatchBuilder batch_builder(&arrow_array); +PAIMON_ASSIGN_OR_RAISE(std::unique_ptr<paimon::RecordBatch> record_batch, + batch_builder.Finish()); +PAIMON_RETURN_NOT_OK(writer->Write(std::move(record_batch))); +PAIMON_ASSIGN_OR_RAISE(std::vector<std::shared_ptr<paimon::CommitMessage>> commit_message, + writer->PrepareCommit()); + +// commit +paimon::CommitContextBuilder commit_context_builder(table_path, commit_user); +PAIMON_ASSIGN_OR_RAISE(std::unique_ptr<paimon::CommitContext> commit_context, + commit_context_builder.SetOptions(options).Finish()); +PAIMON_ASSIGN_OR_RAISE(std::unique_ptr<paimon::FileStoreCommit> committer, + paimon::FileStoreCommit::Create(std::move(commit_context))); +PAIMON_RETURN_NOT_OK(committer->Commit(commit_message)); +``` + +## Batch Read + +### Predicate pushdown + +A `ReadContextBuilder` is used to build reading utils and perform filter and projection pushdown. + Review Comment: `ReadContextBuilder` may be used to pass context to reader, push down and filter is done by reader? -- This is an automated message from the Apache Git Service. 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