Flattening: Reduce memory Footprint.

* Use ijson
* Use pyopenxl write_only mode
* Store sheet lines in an embedded btree ZODB index

#316

Author: kindly

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ### Fixed
 
+- flattening: Uses much less memory by storing data in a embedded ZODB database, using ijson and using write only mode in pyopenxl.
 - use-titles: Use $ref'erring title if available https://github.com/OpenDataServices/flatten-tool/pull/368 
 - create-template --no-deprecated-fields: Did not work if deprecated element at same level as a $ref https://github.com/OpenDataServices/flatten-tool/issues/185#issuecomment-719587348
 

flattentool/__init__.py

@@ -112,7 +112,7 @@ def flatten(
     else:
         schema_parser = None
 
-    parser = JSONParser(
+    with JSONParser(
         json_filename=input_name,
         root_list_path=None if root_is_list else root_list_path,
         schema_parser=schema_parser,
@@ -126,33 +126,33 @@ def flatten(
         preserve_fields=preserve_fields,
         remove_empty_schema_columns=remove_empty_schema_columns,
         truncation_length=truncation_length,
-    )
-    parser.parse()
-
-    def spreadsheet_output(spreadsheet_output_class, name):
-        spreadsheet_output = spreadsheet_output_class(
-            parser=parser,
-            main_sheet_name=main_sheet_name,
-            output_name=name,
-            sheet_prefix=sheet_prefix,
-        )
-        spreadsheet_output.write_sheets()
-
-    if output_format == "all":
-        if not output_name:
-            output_name = "flattened"
-        for format_name, spreadsheet_output_class in OUTPUT_FORMATS.items():
-            spreadsheet_output(
-                spreadsheet_output_class, output_name + FORMATS_SUFFIX[format_name]
+        persist=True,
+    ) as parser:
+
+        def spreadsheet_output(spreadsheet_output_class, name):
+            spreadsheet_output = spreadsheet_output_class(
+                parser=parser,
+                main_sheet_name=main_sheet_name,
+                output_name=name,
+                sheet_prefix=sheet_prefix,
             )
+            spreadsheet_output.write_sheets()
+
+        if output_format == "all":
+            if not output_name:
+                output_name = "flattened"
+            for format_name, spreadsheet_output_class in OUTPUT_FORMATS.items():
+                spreadsheet_output(
+                    spreadsheet_output_class, output_name + FORMATS_SUFFIX[format_name]
+                )
 
-    elif output_format in OUTPUT_FORMATS.keys():  # in dictionary of allowed formats
-        if not output_name:
-            output_name = "flattened" + FORMATS_SUFFIX[output_format]
-        spreadsheet_output(OUTPUT_FORMATS[output_format], output_name)
+        elif output_format in OUTPUT_FORMATS.keys():  # in dictionary of allowed formats
+            if not output_name:
+                output_name = "flattened" + FORMATS_SUFFIX[output_format]
+            spreadsheet_output(OUTPUT_FORMATS[output_format], output_name)
 
-    else:
-        raise Exception("The requested format is not available")
+        else:
+            raise Exception("The requested format is not available")
 
 
 # From http://bugs.python.org/issue16535

flattentool/json_input.py

@@ -7,18 +7,24 @@
 
 import codecs
 import copy
-import json
 import os
+import tempfile
+import uuid
 from collections import OrderedDict
 from decimal import Decimal
 from warnings import warn
 
+import BTrees.OOBTree
+import ijson
+import transaction
 import xmltodict
+import zc.zlibstorage
+import ZODB.FileStorage
 
 from flattentool.i18n import _
 from flattentool.input import path_search
 from flattentool.schema import make_sub_sheet_name
-from flattentool.sheet import Sheet
+from flattentool.sheet import PersistentSheet
 
 BASIC_TYPES = [str, bool, int, Decimal, type(None)]
 
@@ -112,9 +118,26 @@ def __init__(
         remove_empty_schema_columns=False,
         rollup=False,
         truncation_length=3,
+        persist=False,
     ):
+        if persist:
+            self.zodb_db_location = (
+                tempfile.gettempdir() + "/flattentool-" + str(uuid.uuid4())
+            )
+            zodb_storage = zc.zlibstorage.ZlibStorage(
+                ZODB.FileStorage.FileStorage(self.zodb_db_location)
+            )
+            self.db = ZODB.DB(zodb_storage)
+        else:
+            # If None, in memory storage is used.
+            self.db = ZODB.DB(None)
+
+        self.connection = self.db.open()
+        root = self.connection.root
+        root.sheet_store = BTrees.OOBTree.BTree()
+
         self.sub_sheets = {}
-        self.main_sheet = Sheet()
+        self.main_sheet = PersistentSheet(connection=self.connection, name="")
         self.root_list_path = root_list_path
         self.root_id = root_id
         self.use_titles = use_titles
@@ -125,9 +148,17 @@ def __init__(
         self.filter_value = filter_value
         self.remove_empty_schema_columns = remove_empty_schema_columns
         self.seen_paths = set()
+        self.persist = persist
 
         if schema_parser:
-            self.main_sheet = copy.deepcopy(schema_parser.main_sheet)
+            self.main_sheet = PersistentSheet.from_sheet(
+                schema_parser.main_sheet, self.connection
+            )
+            for sheet_name, sheet in list(self.sub_sheets.items()):
+                self.sub_sheets[sheet_name] = PersistentSheet.from_sheet(
+                    sheet, self.connection
+                )
+
             self.sub_sheets = copy.deepcopy(schema_parser.sub_sheets)
             if remove_empty_schema_columns:
                 # Don't use columns from the schema parser
@@ -194,18 +225,13 @@ def __init__(
                 _("Only one of json_file or root_json_dict should be supplied")
             )
 
-        if json_filename:
-            with codecs.open(json_filename, encoding="utf-8") as json_file:
-                try:
-                    self.root_json_dict = json.load(
-                        json_file, object_pairs_hook=OrderedDict, parse_float=Decimal
-                    )
-                except UnicodeError as err:
-                    raise BadlyFormedJSONErrorUTF8(*err.args)
-                except ValueError as err:
-                    raise BadlyFormedJSONError(*err.args)
-        else:
-            self.root_json_dict = root_json_dict
+        if not json_filename:
+            if self.root_list_path is None:
+                self.root_json_list = root_json_dict
+            else:
+                self.root_json_list = path_search(
+                    root_json_dict, self.root_list_path.split("/")
+                )
 
         if preserve_fields:
             # Extract fields to be preserved from input file (one path per line)
@@ -240,19 +266,37 @@ def __init__(
             self.preserve_fields = None
             self.preserve_fields_input = None
 
+        if json_filename:
+            if self.root_list_path is None:
+                path = "item"
+            else:
+                path = root_list_path.replace("/", ".") + ".item"
+
+            json_file = codecs.open(json_filename, encoding="utf-8")
+
+            self.root_json_list = ijson.items(json_file, path, map_type=OrderedDict)
+
+        try:
+            self.parse()
+        except ijson.common.IncompleteJSONError as err:
+            raise BadlyFormedJSONError(*err.args)
+        except UnicodeDecodeError as err:
+            raise BadlyFormedJSONErrorUTF8(*err.args)
+        finally:
+            if json_filename:
+                json_file.close()
+
     def parse(self):
-        if self.root_list_path is None:
-            root_json_list = self.root_json_dict
-        else:
-            root_json_list = path_search(
-                self.root_json_dict, self.root_list_path.split("/")
-            )
-        for json_dict in root_json_list:
+        for num, json_dict in enumerate(self.root_json_list):
             if json_dict is None:
                 # This is particularly useful for IATI XML, in order to not
                 # fall over on empty activity, e.g. <iati-activity/>
                 continue
             self.parse_json_dict(json_dict, sheet=self.main_sheet)
+            if num % 2000 == 0 and num != 0:
+                transaction.commit()
+
+        transaction.commit()
 
         if self.remove_empty_schema_columns:
             # Remove sheets with no lines of data
@@ -501,7 +545,9 @@ def parse_json_dict(
                             parent_name, key, truncation_length=self.truncation_length
                         )
                     if sub_sheet_name not in self.sub_sheets:
-                        self.sub_sheets[sub_sheet_name] = Sheet(name=sub_sheet_name)
+                        self.sub_sheets[sub_sheet_name] = PersistentSheet(
+                            name=sub_sheet_name, connection=self.connection
+                        )
 
                     for json_dict in value:
                         if json_dict is None:
@@ -518,4 +564,16 @@ def parse_json_dict(
                 raise ValueError(_("Unsupported type {}").format(type(value)))
 
         if top:
-            sheet.lines.append(flattened_dict)
+            sheet.append_line(flattened_dict)
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, type, value, traceback):
+        if self.persist:
+            self.connection.close()
+            self.db.close()
+            os.remove(self.zodb_db_location)
+            os.remove(self.zodb_db_location + ".lock")
+            os.remove(self.zodb_db_location + ".index")
+            os.remove(self.zodb_db_location + ".tmp")

flattentool/output.py

@@ -50,7 +50,7 @@ def close(self):
 
 class XLSXOutput(SpreadsheetOutput):
     def open(self):
-        self.workbook = openpyxl.Workbook()
+        self.workbook = openpyxl.Workbook(write_only=True)
 
     def write_sheet(self, sheet_name, sheet):
         sheet_header = list(sheet)
@@ -75,7 +75,6 @@ def write_sheet(self, sheet_name, sheet):
             worksheet.append(line)
 
     def close(self):
-        self.workbook.remove(self.workbook.active)
         self.workbook.save(self.output_name)
 
 

flattentool/sheet.py

@@ -1,3 +1,8 @@
+import copy
+
+import BTrees.IOBTree
+
+
 class Sheet(object):
     """
     An abstract representation of a single sheet of a spreadsheet.
@@ -8,10 +13,14 @@ def __init__(self, columns=None, root_id="", name=None):
         self.id_columns = []
         self.columns = columns if columns else []
         self.titles = {}
-        self.lines = []
+        self._lines = []
         self.root_id = root_id
         self.name = name
 
+    @property
+    def lines(self):
+        return self._lines
+
     def add_field(self, field, id_field=False):
         columns = self.id_columns if id_field else self.columns
         if field not in columns:
@@ -27,3 +36,39 @@ def __iter__(self):
             yield column
         for column in self.columns:
             yield column
+
+    def append_line(self, flattened_dict):
+        self._lines.append(flattened_dict)
+
+
+class PersistentSheet(Sheet):
+    """
+    A sheet that is persisted in ZODB database.
+
+    """
+
+    def __init__(self, columns=None, root_id="", name=None, connection=None):
+        super().__init__(columns=columns, root_id=root_id, name=name)
+        self.connection = connection
+        self.index = 0
+        connection.root.sheet_store[self.name] = BTrees.IOBTree.BTree()
+
+    @property
+    def lines(self):
+        for key, value in self.connection.root.sheet_store[self.name].items():
+            if key % 5000 == 0:
+                self.connection.cacheMinimize()
+            yield value
+
+    def append_line(self, flattened_dict):
+        self.connection.root.sheet_store[self.name][self.index] = flattened_dict
+        self.index += 1
+
+    @classmethod
+    def from_sheet(cls, sheet, connection):
+        instance = cls(name=sheet.name, connection=connection)
+        instance.id_columns = copy.deepcopy(sheet.id_columns)
+        instance.columns = copy.deepcopy(sheet.columns)
+        instance.titles = copy.deepcopy(sheet.titles)
+        instance.root_id = sheet.root_id
+        return instance