Merge 344f11eda6 into b152be7951

This reverts commit 95600da4af.

crates/db_schema/replaceable_schema/triggers.sql

@@ -5,6 +5,12 @@
 -- (even if only other columns are updated) because triggers can run after the deletion of referenced rows and
 -- before the automatic deletion of the row that references it. This is not a problem for insert or delete.
 --
+-- After a row update begins, a concurrent update on the same row can't begin until the whole
+-- transaction that contains the first update is finished. To reduce this locking, statements in
+-- triggers should be ordered based on the likelihood of concurrent writers. For example, updating
+-- site_aggregates should be done last because the same row is updated for all local stuff. If
+-- it were not last, then the locking period for concurrent writers would extend to include the
+-- time consumed by statements that come after.
 --
 --
 -- Create triggers for both post and comments
@@ -27,7 +33,7 @@ AS $a$
 BEGIN
     EXECUTE replace($b$
         -- When a thing gets a vote, update its aggregates and its creator's aggregates
-        CALL r.create_triggers ('thing_like', 'thing_aggregates_and_person_aggregates', $$
+        CALL r.create_triggers ('thing_like', $$
             BEGIN
                 WITH thing_diff AS ( UPDATE
                         thing_aggregates AS a
@@ -38,16 +44,18 @@ BEGIN
                             (thing_like).thing_id, coalesce(sum(count_diff) FILTER (WHERE (thing_like).score = 1), 0) AS upvotes, coalesce(sum(count_diff) FILTER (WHERE (thing_like).score != 1), 0) AS downvotes FROM select_old_and_new_rows AS old_and_new_rows GROUP BY (thing_like).thing_id) AS diff
             WHERE
                 a.thing_id = diff.thing_id
-            RETURNING
-                r.creator_id_from_thing_aggregates (a.*) AS creator_id, diff.upvotes - diff.downvotes AS score)
-        UPDATE
-            person_aggregates AS a
-        SET
-            thing_score = a.thing_score + diff.score FROM (
-                SELECT
-                    creator_id, sum(score) AS score FROM thing_diff GROUP BY creator_id) AS diff
-            WHERE
-                a.person_id = diff.creator_id;
+                    AND (diff.upvotes, diff.downvotes) != (0, 0)
+                RETURNING
+                    r.creator_id_from_thing_aggregates (a.*) AS creator_id, diff.upvotes - diff.downvotes AS score)
+            UPDATE
+                person_aggregates AS a
+            SET
+                thing_score = a.thing_score + diff.score FROM (
+                    SELECT
+                        creator_id, sum(score) AS score FROM thing_diff GROUP BY creator_id) AS diff
+                WHERE
+                    a.person_id = diff.creator_id
+                    AND diff.score != 0;
                 RETURN NULL;
             END;
     $$);
@@ -62,7 +70,7 @@ CALL r.post_or_comment ('post');
 CALL r.post_or_comment ('comment');
 
 -- Create triggers that update counts in parent aggregates
-CALL r.create_triggers ('comment', 'person_aggregates', $$
+CALL r.create_triggers ('comment', $$
 BEGIN
     UPDATE
         person_aggregates AS a
@@ -76,76 +84,56 @@ BEGIN
             r.is_counted (comment)
         GROUP BY (comment).creator_id) AS diff
 WHERE
-    a.person_id = diff.creator_id;
+    a.person_id = diff.creator_id
+        AND diff.comment_count != 0;
 
-RETURN NULL;
-
-END;
-
-$$);
-
-CALL r.create_triggers ('comment', 'site_aggregates', $$
-BEGIN
+WITH post_diff AS (
     UPDATE
-        site_aggregates AS a
+        post_aggregates AS a
     SET
-        comments = a.comments + diff.comments
+        comments = a.comments + diff.comments,
+        newest_comment_time = GREATEST (a.newest_comment_time, (
+                SELECT
+                    published
+                FROM select_new_rows AS new_comment
+                WHERE
+                    a.post_id = new_comment.post_id ORDER BY published DESC LIMIT 1)),
+        newest_comment_time_necro = GREATEST (a.newest_comment_time_necro, (
+                SELECT
+                    published
+                FROM select_new_rows AS new_comment
+                WHERE
+                    a.post_id = new_comment.post_id
+                    -- Ignore comments from the post's creator
+                    AND a.creator_id != new_comment.creator_id
+                    -- Ignore comments on old posts
+                    AND a.published > (new_comment.published - '2 days'::interval)
+                ORDER BY published DESC LIMIT 1))
     FROM (
         SELECT
+            (comment).post_id,
             coalesce(sum(count_diff), 0) AS comments
-        FROM select_old_and_new_rows AS old_and_new_rows
-        WHERE
-            r.is_counted (comment)
-            AND (comment).local) AS diff;
-
-RETURN NULL;
-
-END;
-
-$$);
-
-CALL r.create_triggers ('comment', 'post_aggregates_and_community_aggregates', $$
-BEGIN
-    WITH post_diff AS (
-        UPDATE
-            post_aggregates AS a
-        SET
-            comments = a.comments + diff.comments,
-            newest_comment_time = GREATEST (a.newest_comment_time, (
-                    SELECT
-                        published
-                    FROM select_new_rows AS new_comment
-                    WHERE
-                        a.post_id = new_comment.post_id ORDER BY published DESC LIMIT 1)), newest_comment_time_necro = GREATEST (a.newest_comment_time_necro, (
-                    SELECT
-                        published
-                    FROM select_new_rows AS new_comment
-                    WHERE
-                        a.post_id = new_comment.post_id
-                        -- Ignore comments from the post's creator
-                        AND a.creator_id != new_comment.creator_id
-                        -- Ignore comments on old posts
-                        AND a.published > (new_comment.published - '2 days'::interval)
-                    ORDER BY published DESC LIMIT 1))
-        FROM (
-            SELECT
-                (comment).post_id, coalesce(sum(count_diff), 0) AS comments
-        FROM select_old_and_new_rows AS old_and_new_rows
-        WHERE
-            r.is_counted (comment)
-        GROUP BY (comment).post_id) AS diff
-        LEFT JOIN post ON post.id = diff.post_id
-        WHERE
-            a.post_id = diff.post_id
-        RETURNING
-            a.community_id, diff.comments, r.is_counted (post.*) AS include_in_community_aggregates)
+    FROM
+        select_old_and_new_rows AS old_and_new_rows
+    WHERE
+        r.is_counted (comment)
+    GROUP BY
+        (comment).post_id) AS diff
+    LEFT JOIN post ON post.id = diff.post_id
+    WHERE
+        a.post_id = diff.post_id
+    RETURNING
+        a.community_id,
+        diff.comments,
+        r.is_counted (post.*) AS include_in_community_aggregates)
 UPDATE
     community_aggregates AS a
 SET
     comments = a.comments + diff.comments
 FROM (
     SELECT
-        community_id, sum(comments) AS comments
+        community_id,
+        sum(comments) AS comments
     FROM
         post_diff
     WHERE
@@ -153,7 +141,23 @@ FROM (
     GROUP BY
         community_id) AS diff
 WHERE
-    a.community_id = diff.community_id;
+    a.community_id = diff.community_id
+    AND diff.comments != 0;
+
+UPDATE
+    site_aggregates AS a
+SET
+    comments = a.comments + diff.comments
+FROM (
+    SELECT
+        coalesce(sum(count_diff), 0) AS comments
+    FROM
+        select_old_and_new_rows AS old_and_new_rows
+    WHERE
+        r.is_counted (comment)
+        AND (comment).local) AS diff
+WHERE
+    diff.comments != 0;
 
 RETURN NULL;
 
@@ -161,7 +165,7 @@ END;
 
 $$);
 
-CALL r.create_triggers ('post', 'person_aggregates', $$
+CALL r.create_triggers ('post', $$
 BEGIN
     UPDATE
         person_aggregates AS a
@@ -175,49 +179,41 @@ BEGIN
             r.is_counted (post)
         GROUP BY (post).creator_id) AS diff
 WHERE
-    a.person_id = diff.creator_id;
+    a.person_id = diff.creator_id
+        AND diff.post_count != 0;
 
-RETURN NULL;
-
-END;
-
-$$);
-
-CALL r.create_triggers ('post', 'site_aggregates', $$
-BEGIN
-    UPDATE
-        site_aggregates AS a
-    SET
-        posts = a.posts + diff.posts
-    FROM (
-        SELECT
-            coalesce(sum(count_diff), 0) AS posts
-        FROM select_old_and_new_rows AS old_and_new_rows
-        WHERE
-            r.is_counted (post)
-            AND (post).local) AS diff;
-
-RETURN NULL;
-
-END;
-
-$$);
-
-CALL r.create_triggers ('post', 'community_aggregates', $$
-BEGIN
-    UPDATE
-        community_aggregates AS a
-    SET
-        posts = a.posts + diff.posts
-    FROM (
-        SELECT
-            (post).community_id, coalesce(sum(count_diff), 0) AS posts
-        FROM select_old_and_new_rows AS old_and_new_rows
-        WHERE
-            r.is_counted (post)
-        GROUP BY (post).community_id) AS diff
+UPDATE
+    community_aggregates AS a
+SET
+    posts = a.posts + diff.posts
+FROM (
+    SELECT
+        (post).community_id,
+        coalesce(sum(count_diff), 0) AS posts
+    FROM
+        select_old_and_new_rows AS old_and_new_rows
+    WHERE
+        r.is_counted (post)
+    GROUP BY
+        (post).community_id) AS diff
 WHERE
-    a.community_id = diff.community_id;
+    a.community_id = diff.community_id
+    AND diff.posts != 0;
+
+UPDATE
+    site_aggregates AS a
+SET
+    posts = a.posts + diff.posts
+FROM (
+    SELECT
+        coalesce(sum(count_diff), 0) AS posts
+    FROM
+        select_old_and_new_rows AS old_and_new_rows
+    WHERE
+        r.is_counted (post)
+        AND (post).local) AS diff
+WHERE
+    diff.posts != 0;
 
 RETURN NULL;
 
@@ -225,7 +221,7 @@ END;
 
 $$);
 
-CALL r.create_triggers ('community', 'site_aggregates', $$
+CALL r.create_triggers ('community', $$
 BEGIN
     UPDATE
         site_aggregates AS a
@@ -237,7 +233,9 @@ BEGIN
         FROM select_old_and_new_rows AS old_and_new_rows
         WHERE
             r.is_counted (community)
-            AND (community).local) AS diff;
+            AND (community).local) AS diff
+WHERE
+    diff.communities != 0;
 
 RETURN NULL;
 
@@ -245,7 +243,7 @@ END;
 
 $$);
 
-CALL r.create_triggers ('person', 'site_aggregates', $$
+CALL r.create_triggers ('person', $$
 BEGIN
     UPDATE
         site_aggregates AS a
@@ -255,7 +253,9 @@ BEGIN
         SELECT
             coalesce(sum(count_diff), 0) AS users
         FROM select_old_and_new_rows AS old_and_new_rows
-        WHERE (person).local) AS diff;
+        WHERE (person).local) AS diff
+WHERE
+    diff.users != 0;
 
 RETURN NULL;
 
@@ -290,7 +290,8 @@ BEGIN
             GROUP BY
                 old_post.community_id) AS diff
 WHERE
-    a.community_id = diff.community_id;
+    a.community_id = diff.community_id
+        AND diff.comments != 0;
     RETURN NULL;
 END;
 $$;
@@ -303,7 +304,7 @@ CREATE TRIGGER comment_count
 -- Count subscribers for communities.
 -- subscribers should be updated only when a local community is followed by a local or remote person.
 -- subscribers_local should be updated only when a local person follows a local or remote community.
-CALL r.create_triggers ('community_follower', 'community_aggregates', $$
+CALL r.create_triggers ('community_follower', $$
 BEGIN
     UPDATE
         community_aggregates AS a
@@ -316,7 +317,8 @@ BEGIN
     LEFT JOIN community ON community.id = (community_follower).community_id
     LEFT JOIN person ON person.id = (community_follower).person_id GROUP BY (community_follower).community_id) AS diff
 WHERE
-    a.community_id = diff.community_id;
+    a.community_id = diff.community_id
+        AND (diff.subscribers, diff.subscribers_local) != (0, 0);
 
 RETURN NULL;
 

crates/db_schema/replaceable_schema/utils.sql

@@ -64,46 +64,46 @@ $$;
 --     not allowed for a `DELETE` trigger)
 --   * Transition tables are only provided to the trigger function, not to functions that it calls.
 --
--- The trigger function body is given as the 2nd argument and can contain these names, which are
--- replaced with a `SELECT` statement in parenthesis if needed:
+-- This function can only be called once per table. The trigger function body given as the 2nd argument
+-- and can contain these names, which are replaced with a `SELECT` statement in parenthesis if needed:
 --   * `select_old_rows`
 --   * `select_new_rows`
 --   * `select_old_and_new_rows` with 2 columns:
 --       1. `count_diff`: `-1` for old rows and `1` for new rows, which can be used with `sum` to get the number
 --          to add to a count
 --       2. (same name as the trigger's table): the old or new row as a composite value
-CREATE PROCEDURE r.create_triggers (table_name text, trigger_name text, function_body text)
+CREATE PROCEDURE r.create_triggers (table_name text, function_body text)
 LANGUAGE plpgsql
 AS $a$
 DECLARE
     defs text := $$
     -- Delete
-    CREATE FUNCTION r.thing_trigger_name_for_delete_statement ()
+    CREATE FUNCTION r.thing_delete_statement ()
         RETURNS TRIGGER
         LANGUAGE plpgsql
         AS function_body_delete;
-    CREATE TRIGGER trigger_name_for_delete_statement
+    CREATE TRIGGER delete_statement
         AFTER DELETE ON thing REFERENCING OLD TABLE AS select_old_rows
         FOR EACH STATEMENT
-        EXECUTE FUNCTION r.thing_trigger_name_for_delete_statement ( );
+        EXECUTE FUNCTION r.thing_delete_statement ( );
     -- Insert
-    CREATE FUNCTION r.thing_trigger_name_for_insert_statement ( )
+    CREATE FUNCTION r.thing_insert_statement ( )
         RETURNS TRIGGER
         LANGUAGE plpgsql
         AS function_body_insert;
-    CREATE TRIGGER trigger_name_for_insert_statement
+    CREATE TRIGGER insert_statement
         AFTER INSERT ON thing REFERENCING NEW TABLE AS select_new_rows
         FOR EACH STATEMENT
-        EXECUTE FUNCTION r.thing_trigger_name_for_insert_statement ( );
+        EXECUTE FUNCTION r.thing_insert_statement ( );
     -- Update
-    CREATE FUNCTION r.thing_trigger_name_for_update_statement ( )
+    CREATE FUNCTION r.thing_update_statement ( )
         RETURNS TRIGGER
         LANGUAGE plpgsql
         AS function_body_update;
-    CREATE TRIGGER trigger_name_for_update_statement
+    CREATE TRIGGER update_statement
         AFTER UPDATE ON thing REFERENCING OLD TABLE AS select_old_rows NEW TABLE AS select_new_rows
         FOR EACH STATEMENT
-        EXECUTE FUNCTION r.thing_trigger_name_for_update_statement ( );
+        EXECUTE FUNCTION r.thing_update_statement ( );
     $$;
     select_old_and_new_rows text := $$ (
         SELECT
@@ -135,7 +135,6 @@ DECLARE
             FALSE) $$;
     BEGIN
         function_body := replace(function_body, 'select_old_and_new_rows', select_old_and_new_rows);
-        defs := replace(defs, 'trigger_name', trigger_name);
         -- `select_old_rows` and `select_new_rows` are made available as empty tables if they don't already exist
         defs := replace(defs, 'function_body_delete', quote_literal(replace(function_body, 'select_new_rows', empty_select_new_rows)));
         defs := replace(defs, 'function_body_insert', quote_literal(replace(function_body, 'select_old_rows', empty_select_old_rows)));