[jira] [Commented] (ARROW-14025) [R][C++] PreBuffer is not enabled when scanning parquet via exec nodes

["Neal Richardson (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-14025?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17424096#comment-17424096 ] 

Neal Richardson commented on ARROW-14025:
-----------------------------------------

[~westonpace] is this the right idea (+/- whatever it takes to get it to compile)? I believe this means we also would be getting whatever FragmentScanOptions the dataset was created with (so that we could correctly query CSVs etc.).

{code}
diff --git a/r/src/compute-exec.cpp b/r/src/compute-exec.cpp
index c61f7a3d1..5c60f2ac2 100644
--- a/r/src/compute-exec.cpp
+++ b/r/src/compute-exec.cpp
@@ -113,7 +113,17 @@ std::shared_ptr<compute::ExecNode> ExecNode_Scan(
   arrow::dataset::internal::Initialize();
 
   // TODO: pass in FragmentScanOptions
-  auto options = std::make_shared<arrow::dataset::ScanOptions>();
+  if (dataset->type_name() == "filesystem") {
+    // HALP: dataset is Dataset but needs to be cast to FileSystemDataset
+    // to have format() method
+    auto fmt = dataset->format();
+    auto options = fmt->default_fragment_scan_options;
+    if (fmt->type_name() == "parquet") {
+      options->arrow_reader_properties.pre_buffer_ = true;
+    }
+  } else {
+    auto options = std::make_shared<arrow::dataset::ScanOptions>();
+  }
 
   options->use_async = true;
   options->use_threads = arrow::r::GetBoolOption("arrow.use_threads", true);
{code}

> [R][C++] PreBuffer is not enabled when scanning parquet via exec nodes
> ----------------------------------------------------------------------
>
>                 Key: ARROW-14025
>                 URL: https://issues.apache.org/jira/browse/ARROW-14025
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: C++, R
>            Reporter: Weston Pace
>            Assignee: Neal Richardson
>            Priority: Major
>             Fix For: 6.0.0
>
>
> In ExecNode_Scan a ScanOptions object is built up.  If we are reading parquet we should enable pre-buffering.  This is done by creating a ParquetFragmentScanOptions object and enabling pre-buffering.
> Alternatively, we could just default pre-buffering to true for asynchronous scans of parquet data.



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