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Posted to issues@arrow.apache.org by "Francois Saint-Jacques (Jira)" <ji...@apache.org> on 2020/04/09 14:13:00 UTC
[jira] [Updated] (ARROW-8382) [C++][Dataset] Refactor WritePlan to
decouple from Fragment/Scan/Partition classes
[ https://issues.apache.org/jira/browse/ARROW-8382?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Francois Saint-Jacques updated ARROW-8382:
------------------------------------------
Component/s: C++ - Dataset
> [C++][Dataset] Refactor WritePlan to decouple from Fragment/Scan/Partition classes
> -----------------------------------------------------------------------------------
>
> Key: ARROW-8382
> URL: https://issues.apache.org/jira/browse/ARROW-8382
> Project: Apache Arrow
> Issue Type: Improvement
> Components: C++ - Dataset
> Reporter: Francois Saint-Jacques
> Priority: Major
>
> WritePlan should look like the following.
> {code:c++}
> class ARROW_DS_EXPORT WritePlan {
> public:
> /// Execute the WritePlan and return a FileSystemDataset as a result.
> Result<FileSystemDataset> Execute();
> protected:
> /// The schema of the Dataset which will be written
> std::shared_ptr<Schema> schema;
> /// The format into which fragments will be written
> std::shared_ptr<FileFormat> format;
>
> using SourceAndReader = std::pair<FIleSource, RecordBatchReader>;
> ///
> std::vector<SourceAndReader> outputs;
> };
> {code}
> * Refactor FileFormat::Write(FileSource destination, RecordBatchReader), not sure if it should take the output schema, or the RecordBatchReader should be already of the right schema.
> * Add a class/function that constructs SourceAndReader from Fragments, Partitioning and base path. And remove any Write/Fragment logic from partition.cc.
> * Move Write() out FIleSystemDataset into WritePlan. It could take a FileSystemDatasetFactory to recreate the FileSystemDataset. This is a bonus, not a requirement.
> * Simplify writing routine to avoid the PathTree directory structure, it shouldn't be more complex than `for task in write_tasks: task()`. Not path construction should there.
> The effects are:
> * Simplified WritePlan execution, abstracted away from path construction, and can write to multiple FileSystem and/or Buffers since it doesn't construct the FileSource.
> * By the virtue of using RecordBatchReader instead of Fragment, it isn't tied to writing from Fragment, it can take any construct that yields a RecordBatchReader. It also means that WritePlan doesn't have to know about any Scan related classes.
> * Writing can be done with or without partitioning, this logic is given to whomever generates the SourceAndReader list.
> * Should be simpler to test.
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