core: fix slow group membership lookup (#7688)

src/Simplex/Chat/Store/SQLite/Migrations/chat_query_plans.txt

@@ -5876,11 +5876,11 @@ Query:
     JOIN group_profiles gp ON gp.group_profile_id = g.group_profile_id
     JOIN group_members mu ON mu.group_id = g.group_id
     JOIN contact_profiles pu ON pu.contact_profile_id = COALESCE(mu.member_profile_id, mu.contact_profile_id)
-   WHERE g.group_id = ? AND g.user_id = ? AND mu.contact_id = ?
+   WHERE g.group_id = ? AND g.user_id = ? AND mu.user_id = ? AND mu.contact_id = ?
 Plan:
 SEARCH g USING INTEGER PRIMARY KEY (rowid=?)
 SEARCH gp USING INTEGER PRIMARY KEY (rowid=?)
-SEARCH mu USING INDEX idx_group_members_contact_id (contact_id=?)
+SEARCH mu USING INDEX idx_group_members_group_id (user_id=? AND group_id=?)
 SEARCH pu USING INTEGER PRIMARY KEY (rowid=?)
 
 Query: 

src/Simplex/Chat/Store/Shared.hs

@@ -954,8 +954,9 @@ getGroupInfoRow db cxt User {userId, userContactId} groupId = ExceptT $ do
   firstRow (toGroupInfo currentTs cxt userContactId chatTags) (SEGroupNotFound groupId) $
     DB.query
       db
-      (groupInfoQuery <> " WHERE g.group_id = ? AND g.user_id = ? AND mu.contact_id = ?")
-      (groupId, userId, userContactId)
+      -- mu.user_id steers the planner to idx_group_members_group_id; contact_id index is quadratic over all groups
+      (groupInfoQuery <> " WHERE g.group_id = ? AND g.user_id = ? AND mu.user_id = ? AND mu.contact_id = ?")
+      (groupId, userId, userId, userContactId)
 
 setPreparedGroupLinkInfo_ :: DB.Connection -> GroupInfo -> ConnReqContact -> ConnReqUriHash -> Maybe Int64 -> Maybe Int64 -> UTCTime -> IO ()
 setPreparedGroupLinkInfo_ db GroupInfo {groupId, membership} cReq cReqHash customUserProfileId publicMemberCount_ currentTs = do