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new 06f17bf6 docs(core): correct stale HFile reasoning in metadata-table
reader routing (#723)
06f17bf6 is described below
commit 06f17bf646ca7f8d76230d86f365f171814720cb
Author: Y Ethan Guo <[email protected]>
AuthorDate: Sun Sep 6 10:32:59 2026 -0700
docs(core): correct stale HFile reasoning in metadata-table reader routing
(#723)
---
crates/core/src/file_group/reader.rs | 26 ++++++++++++++++---------
crates/core/src/file_group/reader_v2/adapter.rs | 7 ++++---
2 files changed, 21 insertions(+), 12 deletions(-)
diff --git a/crates/core/src/file_group/reader.rs
b/crates/core/src/file_group/reader.rs
index 79152390..4381d4b9 100644
--- a/crates/core/src/file_group/reader.rs
+++ b/crates/core/src/file_group/reader.rs
@@ -436,10 +436,15 @@ impl FileGroupReader {
/// Which merge implementation serves this read.
///
- /// A metadata table is always served by version 1 whatever the
- /// setting says: its base files and log blocks are HFile, which the
- /// file group reader version 2 has no support for. That is permanent, not
- /// transitional.
+ /// A metadata table is always served by version 1 whatever the setting
+ /// says. Not for want of HFile support — the version 2 engine reads HFile
+ /// base files and log blocks — but because a metadata table's record key,
+ /// merge rule and partition come from its own configuration rather than
+ /// the data table's. The version 2 path for metadata tables is
+ /// the dedicated [`MetadataTableV2Reader`], which reads through the same
+ /// engine with that configuration in hand.
+ ///
+ /// [`MetadataTableV2Reader`]:
crate::metadata::table::v2_reader::MetadataTableV2Reader
///
/// The value is read raw rather than through `get_or_default`, which falls
/// back to the default when a value fails to parse. A typo in the version
@@ -523,11 +528,14 @@ impl FileGroupReader {
// Unreachable while `file_group_reader_version` routes a metadata
table
// to version 1 above; kept so a future change to that routing fails
- // loudly here rather than reaching a reader that cannot read HFile.
+ // loudly here rather than merging metadata records under the data
+ // table's key, merge rule and partition semantics.
if self.is_metadata_table() {
return Err(CoreError::Unsupported(
- "File group reader version 2 cannot read a metadata table's
HFile \
- base files and log blocks"
+ "A metadata table is not read through the generic version 2
path: \
+ its record key, merge rule and partition come from its own \
+ configuration. Version 1 serves it here;
MetadataTableV2Reader \
+ is the version 2 path for metadata tables"
.to_string(),
));
}
@@ -2301,8 +2309,8 @@ mod file_group_reader_version_tests {
/// The guard inside the check, reached only if the dispatch's metadata
/// routing were ever removed. Asserted directly because the dispatch
answers
/// metadata tables before the check runs, so no read can reach it today —
- /// which is exactly why it must keep erroring rather than fall through to
a
- /// reader that cannot read HFile.
+ /// which is exactly why it must keep erroring rather than merge metadata
+ /// records under the data table's key, merge rule and partition semantics.
#[tokio::test]
async fn
test_version_two_unsupported_reason_metadata_table_returns_error() ->
Result<()> {
use crate::config::HudiConfigs;
diff --git a/crates/core/src/file_group/reader_v2/adapter.rs
b/crates/core/src/file_group/reader_v2/adapter.rs
index 056df60b..24c4d30e 100644
--- a/crates/core/src/file_group/reader_v2/adapter.rs
+++ b/crates/core/src/file_group/reader_v2/adapter.rs
@@ -230,9 +230,10 @@ mod tests {
)]))
}
- /// A metadata table is refused rather than attempted. The merge-on-read
- /// reader has no HFile support, so letting it try would fail somewhere
- /// deeper and less clearly.
+ /// A metadata table is refused rather than attempted. Not for want of
+ /// HFile support: its record key, merge rule and partition come from its
+ /// own configuration, so letting this path try would fail somewhere deeper
+ /// and less clearly.
#[test]
fn refuses_a_metadata_table() {
let reason = refuse_reason(true, Some(&schema())).expect("should
refuse");
