liurenjie1024 commented on code in PR #1824:
URL: https://github.com/apache/iceberg-rust/pull/1824#discussion_r2517860151
##########
crates/iceberg/src/arrow/record_batch_transformer.rs:
##########
@@ -111,6 +113,9 @@ enum SchemaComparison {
pub(crate) struct RecordBatchTransformer {
snapshot_schema: Arc<IcebergSchema>,
projected_iceberg_field_ids: Vec<i32>,
+ // Pre-computed constant field information: field_id -> (arrow_type, value)
+ // Avoids duplicate lookups and type conversions during batch processing
+ constant_fields: HashMap<i32, (DataType, PrimitiveLiteral)>,
Review Comment:
We have `Datum` type exactly for `DataType + PrimitiveLiteral`.
##########
crates/iceberg/src/arrow/record_batch_transformer.rs:
##########
@@ -429,6 +471,27 @@ impl RecordBatchTransformer {
let vals: Vec<Option<f64>> = vec![None; num_rows];
Arc::new(Float64Array::from(vals))
}
+ (DataType::RunEndEncoded(_, _),
Some(PrimitiveLiteral::String(value))) => {
Review Comment:
> Should we in general encode constant columns as REE? Or should we make
this custom per field? For the file path it definitely makes sense to run-end
encode.
+1. I can't come up with a reason why we don't do this.
##########
crates/iceberg/src/metadata_columns.rs:
##########
@@ -0,0 +1,97 @@
+// 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.
+
+//! Metadata columns (virtual/reserved fields) for Iceberg tables.
+//!
+//! This module defines metadata columns that can be requested in projections
+//! but are not stored in data files. Instead, they are computed on-the-fly
+//! during reading. Examples include the _file column (file path) and future
+//! columns like partition values or row numbers.
+
+use crate::{Error, ErrorKind, Result};
+
+/// Reserved field ID for the file path (_file) column per Iceberg spec
+pub const RESERVED_FIELD_ID_FILE: i32 = 2147483646;
+
+/// Reserved column name for the file path metadata column
+pub const RESERVED_COL_NAME_FILE: &str = "_file";
+
Review Comment:
Please create a lazy field for `FILE_PATH`, you can take an example here:
https://github.com/apache/iceberg-rust/blob/4eafd2ca22e032c3ee4d9e6abe6ff3eae93e0189/crates/iceberg/src/spec/manifest/entry.rs#L183
Also please don't expose the static field directly, use a method to expose
the field reference.
##########
crates/iceberg/src/metadata_columns.rs:
##########
@@ -0,0 +1,97 @@
+// 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.
+
+//! Metadata columns (virtual/reserved fields) for Iceberg tables.
+//!
+//! This module defines metadata columns that can be requested in projections
+//! but are not stored in data files. Instead, they are computed on-the-fly
+//! during reading. Examples include the _file column (file path) and future
+//! columns like partition values or row numbers.
+
+use crate::{Error, ErrorKind, Result};
+
+/// Reserved field ID for the file path (_file) column per Iceberg spec
+pub const RESERVED_FIELD_ID_FILE: i32 = 2147483646;
Review Comment:
```suggestion
pub const RESERVED_FIELD_ID_FILE: i32 = i32::MAX - 1;
```
This improves readability a little.
##########
crates/iceberg/src/metadata_columns.rs:
##########
@@ -0,0 +1,88 @@
+// 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.
+
+//! Metadata columns (virtual/reserved fields) for Iceberg tables.
+//!
+//! This module defines metadata columns that can be requested in projections
+//! but are not stored in data files. Instead, they are computed on-the-fly
+//! during reading. Examples include the _file column (file path) and future
+//! columns like partition values or row numbers.
+
+use crate::{Error, ErrorKind, Result};
+
+/// Reserved field ID for the file path (_file) column per Iceberg spec
+pub const RESERVED_FIELD_ID_FILE: i32 = 2147483646;
Review Comment:
Please help to create an issue for porting all fields of `MetadataColumns`
here.
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