Block transpose optimization in get_rows

src/block.py

@@ -89,13 +89,23 @@ def get_rows(self):
         if not self.data:
             return self.data
 
-        n_rows = self.rows
+        # Transpose results: columns -> rows.
         n_columns = self.columns
-        # Preallocate memory to avoid .append calls.
-        rv = [None] * n_columns
+        n_rows = self.rows
+
+        flat_data = [None] * n_columns * n_rows
+
+        for j in range(n_columns):
+            column = self.data[j]
+
+            for i in range(n_rows):
+                flat_data[i * n_columns + j] = column[i]
 
-        for i in range(n_columns):
-            rv[i] = tuple([self.data[j][i] for j in range(n_rows)])
+        # Make rows from slices.
+        rv = [None] * n_rows
+        for i in range(n_rows):
+            offset = i * n_columns
+            rv[i] = tuple(flat_data[offset:offset + n_columns])
 
         return rv
 
@@ -121,9 +131,9 @@ def check_dict_row_type(self, row):
             )
 
     @property
-    def rows(self):
+    def columns(self):
         return len(self.data)
 
     @property
-    def columns(self):
-        return len(self.data[0]) if self.rows else 0
+    def rows(self):
+        return len(self.data[0]) if self.columns else 0

src/client.py

@@ -114,10 +114,9 @@ def store_query_result(self, packet, result, columnar=False):
 
         # Header block contains no rows. Pick columns from it.
         if block.rows:
-            if columnar:
-                result.data.extend(block.get_columns())
-            else:
-                result.data.extend(block.get_rows())
+            block_data = block.get_columns() if columnar else block.get_rows()
+            result.data.extend(block_data)
+
         elif not result.columns_with_types:
             result.columns_with_types = block.columns_with_types
 

src/streams/native.py

@@ -19,8 +19,9 @@ def write(self, block):
         if self.server_revision >= defines.DBMS_MIN_REVISION_WITH_BLOCK_INFO:
             block.info.write(self.fout)
 
-        n_columns = block.columns
-        n_rows = block.rows
+        # We write transposed data.
+        n_columns = block.rows
+        n_rows = block.columns
 
         write_varint(n_columns, self.fout)
         write_varint(n_rows, self.fout)
@@ -29,7 +30,7 @@ def write(self, block):
             write_binary_str(col_name, self.fout)
             write_binary_str(col_type, self.fout)
 
-            if n_rows:
+            if n_columns:
                 try:
                     items = [row[i] for row in block.data]
                 except IndexError: