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refactor(mdb): use safe conn.execute() for fetch_table_row_count #92

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Merged
lewiszlw merged 3 commits into from
Jun 22, 2026
Merged

refactor(mdb): use safe conn.execute() for fetch_table_row_count #92

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62b1cab
refactor(mdb): remove dummy bind_col workaround from query path
lewiszlw Jun 22, 2026
bd819b5
chore: trigger CI
lewiszlw Jun 22, 2026
465fc71
refactor(mdb): use safe conn.execute() for fetch_table_row_count
lewiszlw Jun 22, 2026
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83 changes: 20 additions & 63 deletions remote-table/src/connection/mdb/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,7 @@ use datafusion_physical_plan::stream::RecordBatchStreamAdapter;
use futures::lock::Mutex;
use log::debug;
use odbc_api::Environment;
use odbc_api::handles::{AsStatementRef, SqlResult, SqlText, Statement, StatementImpl};
use odbc_api::handles::{SqlResult, SqlText, Statement, StatementImpl};
use odbc_api::{Cursor, CursorImpl};
use std::collections::HashMap;
use std::path::PathBuf;
Expand Down Expand Up @@ -249,28 +249,6 @@ impl Connection for MdbConnection {
))
})?;

// mdbtools 1.0.x requires SQLBindCol before SQLFetch — without it,
// SQLFetch hangs indefinitely. odbc-api's Cursor::next_row() calls
// SQLFetch without binding columns.
//
// Workaround: bind a single dummy column (column 1) to allow
// SQLFetch to proceed, then use the row-by-row Cursor::next_row()
// path which calls SQLGetData for each cell. SQLGetData after
// SQLBindCol works because the dummy buffer is ignored.
let mut dummy = odbc_api::Nullable::<i32>::null();
match unsafe { cursor.as_stmt_ref().bind_col(1, &mut dummy) } {
SqlResult::Success(()) | SqlResult::SuccessWithInfo(()) => {}
SqlResult::Error { function } => {
return Err(DataFusionError::Execution(format!(
"{function} failed binding dummy column for mdb"
)));
}
other => {
return Err(DataFusionError::Execution(format!(
"Unexpected result binding dummy column: {other:?}"
)));
}
}
let mut exhausted = false;

loop {
Expand Down Expand Up @@ -379,54 +357,33 @@ impl MdbConnection {
tokio::task::spawn_blocking(move || {
let handle = Handle::current();
let conn = handle.block_on(async { conn.lock().await });
let pre = conn.preallocate().map_err(|e| {
DataFusionError::Execution(format!(
"Failed to preallocate statement for MDB row count: {e:?}"
))
})?;
let mut stmt = pre.into_handle();
let sql_text = SqlText::new(&count_query);
// SAFETY: `count_query` is owned by this closure and outlives `stmt`.
if unsafe { stmt.exec_direct(&sql_text) }.is_err() {
return Err(DataFusionError::Execution(format!(
"Failed to execute MDB row count query: {count_query}"
)));
}

// mdbtools ODBC returns 0 for aggregate COUNT(*) even though
// mdb-sql returns the correct value. Count table rows by fetching
// the first column instead; this keeps COUNT pushdown table-only
// without materializing Arrow batches.
let mut dummy = odbc_api::Nullable::<i32>::null();
match unsafe { stmt.bind_col(1, &mut dummy) } {
SqlResult::Success(()) | SqlResult::SuccessWithInfo(()) => {}
SqlResult::Error { function } => {
return Err(DataFusionError::Execution(format!(
"{function} failed binding MDB row-count column"
)));
}
other => {
return Err(DataFusionError::Execution(format!(
"Unexpected result binding MDB row-count column: {other:?}"
)));
}
}
// mdb-sql returns the correct value. Count table rows by iterating
// the cursor instead.
let mut cursor = conn
.execute(&count_query, (), None)
.map_err(|e| {
DataFusionError::Execution(format!(
"Failed to execute MDB row count query: {e:?}, sql: {count_query}"
))
})?
.ok_or_else(|| {
DataFusionError::Execution(format!(
"No result set for MDB row count query: {count_query}"
))
})?;

let mut row_count = 0usize;
loop {
match unsafe { stmt.fetch() } {
SqlResult::Success(()) | SqlResult::SuccessWithInfo(()) => {
match cursor.next_row() {
Ok(Some(_row)) => {
row_count += 1;
}
SqlResult::NoData => break,
SqlResult::Error { function } => {
return Err(DataFusionError::Execution(format!(
"{function} failed fetching MDB row count"
)));
}
other => {
Ok(None) => break,
Err(e) => {
return Err(DataFusionError::Execution(format!(
"Unexpected result fetching MDB row count: {other:?}"
"Failed fetching MDB row count: {e}"
)));
}
}
Expand Down