Improve share list speed using lazy='subquery'

lazy='immediate' leads to each relationship being collected when
it is accessed. This results in at least three extra queries when
we query for all share details. lazy='subquery' collects all data
when the query is executed. In this commit we only changed code for
improving the share list with details ("manila list") speed.

Change-Id: Ia61b108ece0817069737980a614cc6c15c1a3507
Closes-Bug: #1859785
Co-authored-by: Johannes Kulik <johannes.kulik@sap.com>
Co-authored-by: Maurice Escher <maurice.escher@sap.com>
(cherry picked from commit 54c5667e6b)

manila/db/sqlalchemy/models.py

@@ -318,7 +318,7 @@ class Share(BASE, ManilaBase):
     task_state = Column(String(255))
     instances = orm.relationship(
         "ShareInstance",
-        lazy='immediate',
+        lazy='subquery',
         primaryjoin=(
             'and_('
             'Share.id == ShareInstance.share_id, '
@@ -388,7 +388,7 @@ class ShareInstance(BASE, ManilaBase):
                                   nullable=True)
     _availability_zone = orm.relationship(
         "AvailabilityZone",
-        lazy='immediate',
+        lazy='subquery',
         foreign_keys=availability_zone_id,
         primaryjoin=(
             'and_('
@@ -415,7 +415,7 @@ class ShareInstance(BASE, ManilaBase):
                              nullable=True)
     share_type = orm.relationship(
         "ShareTypes",
-        lazy='immediate',
+        lazy='subquery',
         foreign_keys=share_type_id,
         primaryjoin='and_('
                     'ShareInstance.share_type_id == ShareTypes.id, '

releasenotes/notes/bug-1859785-share-list-speed-6b09e7717624e037.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Improved share list speed using lazy='subquery'. The sqlalchemy models of
+    Share and Share Instance relationships previously had lazy='immediate'.
+    This resulted in at least three extra queries when we queried for all share
+    details.