Further improve memory usage for CSV rendering

- Dump sheets to a json var, delete the sheets before rendering.
- Delete reader when exception happens
- Update error message for TableTooBigError
- Update comment and log for garbage collection

mfr/extensions/tabular/libs/stdlib_tools.py

@@ -19,8 +19,8 @@ def csv_stdlib(fp):
         dialect = csv.excel
     else:
         _set_dialect_quote_attrs(dialect, data)
-
     del data
+
     reader = csv.DictReader(fp, dialect=dialect)
     columns = []
     # update the reader field names to avoid duplicate column names when performing row extraction
@@ -41,6 +41,7 @@ def csv_stdlib(fp):
     try:
         rows = [row for row in reader]
     except csv.Error as e:
+        del reader
         if any("field larger than field limit" in errorMsg for errorMsg in e.args):
             raise TabularRendererError(
                 'This file contains a field too large to render. '
@@ -51,10 +52,9 @@ def csv_stdlib(fp):
         else:
             raise TabularRendererError('csv.Error: {}'.format(e), extension='csv') from e
 
+    del reader
     if not columns and not rows:
         raise EmptyTableError('Table empty or corrupt.', extension='csv')
-
-    del reader
     return {'Sheet 1': (columns, rows)}
 
 

mfr/extensions/tabular/render.py

@@ -33,21 +33,27 @@ def render(self):
         with open(self.file_path, errors='replace') as fp:
             sheets, size, nbr_rows, nbr_cols = self._render_grid(fp, self.metadata.ext)
 
-        # Force GC
-        gc.collect()
-
         if sheets and size:
+            json_sheets = json.dumps(sheets)
+            del sheets
+            # Forcing garbage collection accelerates the memory free/release process with a small
+            # but acceptable cost in performance
+            nbr_objs = gc.collect()
+            logger.debug('Number of unreachable objects collected: {}'.format(nbr_objs))
             return self.TEMPLATE.render(
                 base=self.assets_url,
                 width=settings.TABLE_WIDTH,
                 height=settings.TABLE_HEIGHT,
-                sheets=json.dumps(sheets),
+                sheets=json_sheets,
                 options=json.dumps(size),
             )
 
+        nbr_objs = gc.collect()
+        logger.debug('Number of unreachable objects collected: {}'.format(nbr_objs))
         assert nbr_rows and nbr_cols
         raise exceptions.TableTooBigError(
-            'Table is too large to render.',
+            'Table with more than {} rows or columns are not rendered. Please download the file to '
+            'view.'.format(settings.MAX_SIZE),
             extension=self.metadata.ext,
             nbr_cols=nbr_cols,
             nbr_rows=nbr_rows