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Concurrent Parquet Schema Inference #6366

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May 19, 2023
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Concurrent Parquet Schema Inference #6366

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13 changes: 7 additions & 6 deletions datafusion/core/src/datasource/file_format/parquet.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@ use async_trait::async_trait;
use bytes::{BufMut, BytesMut};
use datafusion_common::DataFusionError;
use datafusion_physical_expr::PhysicalExpr;
use futures::{StreamExt, TryStreamExt};
use hashbrown::HashMap;
use object_store::{ObjectMeta, ObjectStore};
use parquet::arrow::parquet_to_arrow_schema;
Expand Down Expand Up @@ -151,12 +152,12 @@ impl FileFormat for ParquetFormat {
store: &Arc<dyn ObjectStore>,
objects: &[ObjectMeta],
) -> Result<SchemaRef> {
let mut schemas = Vec::with_capacity(objects.len());
for object in objects {
let schema =
fetch_schema(store.as_ref(), object, self.metadata_size_hint).await?;
schemas.push(schema)
}
let schemas: Vec<_> = futures::stream::iter(objects)
.map(|object| fetch_schema(store.as_ref(), object, self.metadata_size_hint))
.boxed() // Workaround https://github.com/rust-lang/rust/issues/64552
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No I cannot explain why this works... But for some unknown reason it placates the compiler

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I found using streams was a similarly frustrating experience where the compiler give you an opaque error message (and opaque is being polite)

.buffered(32)
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I think the 32 should at least be a named constant so it is more discoverable

What do you think about potentially using the same value as in #6183:

const CONCURRENCY_LIMIT: usize = 100;

(I sort of imagine some day someone will want to make that a configuration knob rather than a constant so using the same constant in the code will make it easier to find where they are used)

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I'll make this change as a follow up

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#6389

.try_collect()
.await?;

let schema = if self.skip_metadata(state.config_options()) {
Schema::try_merge(clear_metadata(schemas))
Expand Down