gists: define and use explicit Mercurial backend to speed up creation and fetching of backend repo

rhodecode/apps/gist/views.py

@@ -67,7 +67,6 b' class GistView(BaseAppView):'
             (Gist.ACL_LEVEL_PUBLIC, _("Can be accessed by anonymous users"))
         ]
 
-
         return c
 
     @LoginRequired()

rhodecode/model/db.py

@@ -4260,9 +4260,16 b' class Gist(Base, BaseModel):'
     # SCM functions
 
     def scm_instance(self, **kwargs):
+        """
+        Get explicit Mercurial repository used
+        :param kwargs:
+        :return:
+        """
+        from rhodecode.model.gist import GistModel
         full_repo_path = os.path.join(self.base_path(), self.gist_access_id)
         return get_vcs_instance(
-            repo_path=safe_str(full_repo_path), create=False)
+            repo_path=safe_str(full_repo_path), create=False,
+            _vcs_alias=GistModel.vcs_backend)
 
 
 class ExternalIdentity(Base, BaseModel):

rhodecode/model/gist.py

@@ -47,6 +47,7 b" GIST_METADATA_FILE = '.rc_gist_metadata'"
 
 class GistModel(BaseModel):
     cls = Gist
+    vcs_backend = 'hg'
 
     def _get_gist(self, gist):
         """
@@ -145,7 +146,7 b' class GistModel(BaseModel):'
         gist_repo_path = os.path.join(GIST_STORE_LOC, gist_id)
         log.debug('Creating new %s GIST repo in %s', gist_type, gist_repo_path)
         repo = RepoModel()._create_filesystem_repo(
-            repo_name=gist_id, repo_type='hg', repo_group=GIST_STORE_LOC,
+            repo_name=gist_id, repo_type=self.vcs_backend, repo_group=GIST_STORE_LOC,
             use_global_config=True)
 
         # now create single multifile commit