[GitHub] [arrow] aucahuasi commented on a diff in pull request #14226: ARROW-17599: [C++] Change the way how arrow reads parquet buffered files

[GitBox]

aucahuasi commented on code in PR #14226:
URL: https://github.com/apache/arrow/pull/14226#discussion_r996432256


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cpp/src/parquet/arrow/reader.cc:
##########
@@ -1107,8 +1112,13 @@ class RowGroupGenerator {
     if (!reader->properties().pre_buffer()) {
       row_group_read = SubmitRead(cpu_executor_, reader, row_group, 
column_indices);
     } else {
+      reader->parquet_reader()->PreBuffer({row_group}, column_indices_,
+                                          reader_properties_.io_context(),
+                                          reader_properties_.cache_options());
       auto ready = reader->parquet_reader()->WhenBuffered({row_group}, 
column_indices);
       if (cpu_executor_) ready = cpu_executor_->TransferAlways(ready);
+      // wait for buffering the rowgroup before read it
+      ready.Wait();

Review Comment:
   It seems -somehow- when for the same rowgroup we trigger `ReadOneRowGroup` 
and it starts reading, the cache entries are empty (even when I could confirm 
that it called `PreBuffer` before)
   I did a simple change: when we don't transfer the future using
   `if (cpu_executor_) ready = cpu_executor_->TransferAlways(ready);`
   it works without wait.



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