Repository: NatLibFi/Annif
Issue category: Performance Issue

Share vocabulary objects between projects
Currently, each AnnifProject creates its own vocabulary (AnnifVocabulary object, which wraps a SubjectIndex) even though in reality many projects may use the same vocabulary - which is now even more likely since vocabularies are multilingual (#600). This leads to unnecessary use of RAM and also CPU when the subject index has to be recreated many times.

Instead, the vocabularies could be moved under AnnifRegistry which currently only stores projects. The vocabularies could be loaded lazily as needed using a get_vocab method, similar to the current get_vocab method in annif.vocab.
Share vocabulary objects between projects
Currently, each AnnifProject creates its own vocabulary (AnnifVocabulary object, which wraps a SubjectIndex) even though in reality many projects may use the same vocabulary - which is now even more likely since vocabularies are multilingual (#600). This leads to unnecessary use of RAM and also CPU when the subject index has to be recreated many times.

Instead, the vocabularies could be moved under AnnifRegistry which currently only stores projects. The vocabularies could be loaded lazily as needed using a get_vocab method, similar to the current get_vocab method in annif.vocab.


Functions to edit:
annif/project.py:AnnifProject.vocab
annif/registry.py:AnnifRegistry.__init__
annif/registry.py:AnnifRegistry._create_projects
annif/registry.py:AnnifRegistry
annif/vocab.py:get_vocab
Functions added: annif/registry.py:AnnifRegistry.get_vocab

Patch:
diff --git a/annif/project.py b/annif/project.py
index 13f470fcb..05fa7353f 100644
--- a/annif/project.py
+++ b/annif/project.py
@@ -9,7 +9,6 @@
 import annif.corpus
 import annif.suggestion
 import annif.backend
-import annif.vocab
 from annif.datadir import DatadirMixin
 from annif.exception import AnnifException, ConfigurationException, \
     NotSupportedException, NotInitializedException
@@ -155,9 +154,8 @@ def vocab(self):
             if self.vocab_spec is None:
                 raise ConfigurationException("vocab setting is missing",
                                              project_id=self.project_id)
-            self._vocab = annif.vocab.get_vocab(self.vocab_spec,
-                                                self._base_datadir,
-                                                self.language)
+            self._vocab = self.registry.get_vocab(self.vocab_spec,
+                                                  self.language)
 
         return self._vocab
 
diff --git a/annif/registry.py b/annif/registry.py
index 878ccfbdb..a56340ab0 100644
--- a/annif/registry.py
+++ b/annif/registry.py
@@ -1,35 +1,41 @@
 """Registry that keeps track of Annif projects"""
 
 import collections
+import re
 from flask import current_app
 import annif
 from annif.config import parse_config
 from annif.project import Access, AnnifProject
+from annif.vocab import AnnifVocabulary
+from annif.util import parse_args
 
 logger = annif.logger
 
 
 class AnnifRegistry:
-    """Class that keeps track of the Annif projects"""
-
-    # Note: The individual projects are stored in a shared static variable,
-    # keyed by the "registry ID" which is unique to the registry instance.
-    # This is done to make it possible to serialize AnnifRegistry instances
-    # without including the potentially huge project objects (which contain
-    # backends with large models, vocabularies with lots of concepts etc).
-    # Serialized AnnifRegistry instances can then be passed between
-    # processes when using the multiprocessing module.
+    """Class that keeps track of the Annif projects and vocabularies"""
+
+    # Note: The individual projects and vocabularies are stored in shared
+    # static variables, keyed by the "registry ID" which is unique to the
+    # registry instance. This is done to make it possible to serialize
+    # AnnifRegistry instances without including the potentially huge objects
+    # (which contain backends with large models, vocabularies with lots of
+    # concepts etc). Serialized AnnifRegistry instances can then be passed
+    # between processes when using the multiprocessing module.
     _projects = {}
+    _vocabs = {}
 
     def __init__(self, projects_config_path, datadir, init_projects):
         self._rid = id(self)
+        self._datadir = datadir
         self._projects[self._rid] = \
-            self._create_projects(projects_config_path, datadir)
+            self._create_projects(projects_config_path)
+        self._vocabs[self._rid] = {}
         if init_projects:
             for project in self._projects[self._rid].values():
                 project.initialize()
 
-    def _create_projects(self, projects_config_path, datadir):
+    def _create_projects(self, projects_config_path):
         # parse the configuration
         config = parse_config(projects_config_path)
 
@@ -42,7 +48,7 @@ def _create_projects(self, projects_config_path, datadir):
         for project_id in config.project_ids:
             projects[project_id] = AnnifProject(project_id,
                                                 config[project_id],
-                                                datadir,
+                                                self._datadir,
                                                 self)
         return projects
 
@@ -64,6 +70,23 @@ def get_project(self, project_id, min_access=Access.private):
         except KeyError:
             raise ValueError("No such project {}".format(project_id))
 
+    def get_vocab(self, vocab_spec, default_language):
+        """Return an AnnifVocabulary corresponding to the vocab_spec. If no
+        language information is specified, use the given default language."""
+        match = re.match(r'(\w+)(\((.*)\))?', vocab_spec)
+        if match is None:
+            raise ValueError(
+                f"Invalid vocabulary specification: {vocab_spec}")
+        vocab_id = match.group(1)
+        posargs, kwargs = parse_args(match.group(3))
+        language = posargs[0] if posargs else default_language
+        vocab_key = (vocab_id, language)
+
+        if vocab_key not in self._vocabs[self._rid]:
+            self._vocabs[self._rid][vocab_key] = AnnifVocabulary(
+                vocab_id, self._datadir, language)
+        return self._vocabs[self._rid][vocab_key]
+
 
 def initialize_projects(app):
     projects_config_path = app.config['PROJECTS_CONFIG_PATH']
diff --git a/annif/vocab.py b/annif/vocab.py
index da57ec6cb..9605bdf9b 100644
--- a/annif/vocab.py
+++ b/annif/vocab.py
@@ -1,28 +1,15 @@
 """Vocabulary management functionality for Annif"""
 
 import os.path
-import re
 import annif
 import annif.corpus
 import annif.util
 from annif.datadir import DatadirMixin
 from annif.exception import NotInitializedException
-from annif.util import parse_args
 
 logger = annif.logger
 
 
-def get_vocab(vocab_spec, datadir, default_language):
-    match = re.match(r'(\w+)(\((.*)\))?', vocab_spec)
-    if match is None:
-        raise ValueError(f"Invalid vocabulary specification: {vocab_spec}")
-    vocab_id = match.group(1)
-    posargs, kwargs = parse_args(match.group(3))
-    language = posargs[0] if posargs else default_language
-
-    return AnnifVocabulary(vocab_id, datadir, language)
-
-
 class AnnifVocabulary(DatadirMixin):
     """Class representing a subject vocabulary which can be used by multiple
     Annif projects."""

Test patch: diff --git a/tests/test_vocab.py b/tests/test_vocab.py
index 68f0cb983..02225ce16 100644
--- a/tests/test_vocab.py
+++ b/tests/test_vocab.py
@@ -19,9 +19,9 @@ def load_dummy_vocab(tmpdir):
     return vocab
 
 
-def test_get_vocab_invalid():
+def test_get_vocab_invalid(registry):
     with pytest.raises(ValueError) as excinfo:
-        annif.vocab.get_vocab('', None, None)
+        registry.get_vocab('', None)
     assert 'Invalid vocabulary specification' in str(excinfo.value)