Add two new setting options to control the caching of page images.

DOCUMENTS_DISABLE_BASE_IMAGE_CACHE and
DOCUMENTS_DISABLE_TRANSFORMED_IMAGE_CACHE.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

docs/releases/2.5.rst

@@ -65,6 +65,18 @@ Other Changes
 - Add "Remember me" checkbox in the login form.
 - Add AUTHENTICATION_MAXIMUM_SESSION_LENGTH configuration setting for the maximum
   time an user's login session will remain valid. Defaults to 30 days.
+- Ability to disable the document page image caching. This feature is controlled
+  by two new settings: DOCUMENTS_DISABLE_TRANSFORMED_IMAGE_CACHE and 
+  DOCUMENTS_DISABLE_BASE_IMAGE_CACHE. DOCUMENTS_DISABLE_BASE_IMAGE_CACHE
+  disables the first layer of caching, the generation of a master image file
+  for each document page. This means that subsequent request for a page's
+  image will trigger the conversion of the document from its original
+  uploaded file. The second option, DOCUMENTS_DISABLE_TRANSFORMED_IMAGE_CACHE,
+  disables just the caching of the transformed (rotated, resized, zoomed)
+  images of document pages. The settings can be used together or separately 
+  depending on how much disk space saving is desired. These settings give control
+  over the trade-off between disk space savings and higher CPU utilization.
+ 
 
 Removals
 --------

mayan/apps/documents/models.py

@@ -36,6 +36,7 @@ from .managers import (
 from .permissions import permission_document_view
 from .runtime import cache_storage_backend, storage_backend
 from .settings import (
+    setting_disable_base_image_cache, setting_disable_transformed_image_cache,
     setting_display_size, setting_language, setting_zoom_max_level,
     setting_zoom_min_level
 )
@@ -768,11 +769,14 @@ class DocumentPage(models.Model):
         # Check is transformed image is available
         logger.debug('transformations cache filename: %s', cache_filename)
 
-        if cache_storage_backend.exists(cache_filename):
+        if not setting_disable_transformed_image_cache.value and cache_storage_backend.exists(cache_filename):
             logger.debug(
                 'transformations cache file "%s" found', cache_filename
             )
         else:
+            logger.debug(
+                'transformations cache file "%s" not found', cache_filename
+            )
             image = self.get_image(transformations=transformation_list)
             with cache_storage_backend.open(cache_filename, 'wb+') as file_object:
                 file_object.write(image.getvalue())
@@ -785,7 +789,7 @@ class DocumentPage(models.Model):
         cache_filename = self.cache_filename
         logger.debug('Page cache filename: %s', cache_filename)
 
-        if cache_storage_backend.exists(cache_filename):
+        if not setting_disable_base_image_cache.value and cache_storage_backend.exists(cache_filename):
             logger.debug('Page cache file "%s" found', cache_filename)
             converter = converter_class(
                 file_object=cache_storage_backend.open(cache_filename)

mayan/apps/documents/settings.py

@@ -73,3 +73,18 @@ setting_language_choices = namespace.add_setting(
     global_name='DOCUMENTS_LANGUAGE_CHOICES', default=LANGUAGE_CHOICES,
     help_text=_('List of supported document languages.')
 )
+setting_disable_base_image_cache = namespace.add_setting(
+    global_name='DOCUMENTS_DISABLE_BASE_IMAGE_CACHE', default=False,
+    help_text=_(
+        'Disables the first cache tier which stores high resolution, '
+        'non transformed versions of documents\'s pages.'
+    )
+)
+setting_disable_transformed_image_cache = namespace.add_setting(
+    global_name='DOCUMENTS_DISABLE_TRANSFORMED_IMAGE_CACHE', default=False,
+    help_text=_(
+        'Disables the second cache tier which stores medium to low '
+        'resolution, transformed (rotated, zoomed, etc) versions '
+        'of documents\' pages.'
+    )
+)