Shorten topic re-visit "grace period" to 30 sec

tildes/alembic/versions/9b7a7b906956_shorten_topic_re_visit_grace_period.py

@@ -0,0 +1,58 @@
+"""Shorten topic re-visit grace period
+
+Revision ID: 9b7a7b906956
+Revises: 4241b0202fd4
+Create Date: 2020-02-07 18:45:43.867078
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = "9b7a7b906956"
+down_revision = "4241b0202fd4"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.execute(
+        """
+        create or replace function prevent_recent_repeat_visits() returns trigger as $$
+        begin
+            perform * from topic_visits
+                where user_id = NEW.user_id
+                    and topic_id = NEW.topic_id
+                    and visit_time >= now() - interval '30 seconds';
+
+            if (FOUND) then
+                return null;
+            else
+                return NEW;
+            end if;
+        end;
+        $$ language plpgsql;
+    """
+    )
+
+
+def downgrade():
+    op.execute(
+        """
+        create or replace function prevent_recent_repeat_visits() returns trigger as $$
+        begin
+            perform * from topic_visits
+                where user_id = NEW.user_id
+                    and topic_id = NEW.topic_id
+                    and visit_time >= now() - interval '2 minutes';
+
+            if (FOUND) then
+                return null;
+            else
+                return NEW;
+            end if;
+        end;
+        $$ language plpgsql;
+    """
+    )

tildes/sql/init/triggers/topic_visits/topic_visits.sql

@@ -7,7 +7,7 @@ begin
     perform * from topic_visits
         where user_id = NEW.user_id
             and topic_id = NEW.topic_id
-            and visit_time >= now() - interval '2 minutes';
+            and visit_time >= now() - interval '30 seconds';
 
     if (FOUND) then
         return null;