Function delete_by_merge 

pub async fn delete_by_merge(
    table: DeltaTable,
    delete_batch: RecordBatch,
    key_columns: &[String],
    writer_id: &str,
    epoch: u64,
) -> Result<(DeltaTable, usize), ConnectorError>

Performs a DELETE-by-merge for rows to be removed from the target table.

Matches source (delete) rows by key_columns and deletes matching target rows.

Errors

Returns ConnectorError::WriteError if the operation fails.