grishka/lemmy
1
0
Fork 0
Code Issues Pull requests Projects Releases Wiki Activity

Optimize stuff in attempt to fix high amount of locks, and fix comment_aggregates.child_count (#4696)

Browse source 
* separate triggers

* auto_explain.log_triggers=on

* Revert "auto_explain.log_triggers=on"

This reverts commit 078b2dbb9bbb878078f1089cffda06b6458d127c.

* Revert "separate triggers"

This reverts commit 95600da4afb49e1dc203c2d61da4c57858e107db.

* bring back migration

* re-order statements

* add comment about statement ordering

* no redundant updates

* optimize post_aggregates update in comment trigger

* set comment path in trigger

* update comment_aggregates.child_count using trigger

* move `LEFT JOIN post` to inner query

* clean up newest_comment_time_necro

* add down.sql
This commit is contained in:
dullbananas 2024-05-09 05:18:55 -07:00 committed by GitHub
parent b4f9ef24a5
commit c4fc3a8ede
No known key found for this signature in database
GPG key ID: B5690EEEBB952194
4 changed files with 179 additions and 141 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

194
crates/db_schema/replaceable_schema/triggers.sql
View file

@ -5,6 +5,12 @@
-- (even if only other columns are updated) because triggers can run after the deletion of referenced rows and -- (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. -- 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 -- Create triggers for both post and comments
@ -38,6 +44,7 @@ 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 (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 WHERE
a.thing_id = diff.thing_id a.thing_id = diff.thing_id
AND (diff.upvotes, diff.downvotes) != (0, 0)
RETURNING RETURNING
r.creator_id_from_thing_aggregates (a.*) AS creator_id, diff.upvotes - diff.downvotes AS score) r.creator_id_from_thing_aggregates (a.*) AS creator_id, diff.upvotes - diff.downvotes AS score)
UPDATE UPDATE
@ -47,7 +54,8 @@ BEGIN
SELECT SELECT
creator_id, sum(score) AS score FROM thing_diff GROUP BY creator_id) AS diff creator_id, sum(score) AS score FROM thing_diff GROUP BY creator_id) AS diff
WHERE WHERE
a.person_id = diff.creator_id; a.person_id = diff.creator_id
AND diff.score != 0;
RETURN NULL; RETURN NULL;
END; END;
$$); $$);
@ -62,6 +70,21 @@ CALL r.post_or_comment ('post');
CALL r.post_or_comment ('comment'); CALL r.post_or_comment ('comment');
-- Create triggers that update counts in parent aggregates -- Create triggers that update counts in parent aggregates
CREATE FUNCTION r.parent_comment_ids (path ltree)
RETURNS SETOF int
LANGUAGE sql
IMMUTABLE parallel safe
BEGIN
ATOMIC
SELECT
comment_id::int
FROM
string_to_table (ltree2text (path), '.') AS comment_id
-- Skip first and last
LIMIT (nlevel (path) - 2) OFFSET 1;
END;
CALL r.create_triggers ('comment', $$ CALL r.create_triggers ('comment', $$
BEGIN BEGIN
UPDATE UPDATE
@ -76,60 +99,84 @@ BEGIN
r.is_counted (comment) r.is_counted (comment)
GROUP BY (comment).creator_id) AS diff GROUP BY (comment).creator_id) AS diff
WHERE WHERE
a.person_id = diff.creator_id; a.person_id = diff.creator_id
AND diff.comment_count != 0;
UPDATE UPDATE
site_aggregates AS a comment_aggregates AS a
SET SET
comments = a.comments + diff.comments child_count = a.child_count + diff.child_count
FROM ( FROM (
SELECT SELECT
coalesce(sum(count_diff), 0) AS comments parent_id,
coalesce(sum(count_diff), 0) AS child_count
FROM (
-- For each inserted or deleted comment, this outputs 1 row for each parent comment.
-- For example, this:
--
-- count_diff | (comment).path
-- ------------+----------------
-- 1 | 0.5.6.7
-- 1 | 0.5.6.7.8
--
-- becomes this:
--
-- count_diff | parent_id
-- ------------+-----------
-- 1 | 5
-- 1 | 6
-- 1 | 5
-- 1 | 6
-- 1 | 7
SELECT
count_diff,
parent_id
FROM FROM
select_old_and_new_rows AS old_and_new_rows select_old_and_new_rows AS old_and_new_rows,
LATERAL r.parent_comment_ids ((comment).path) AS parent_id) AS expanded_old_and_new_rows
GROUP BY
parent_id) AS diff
WHERE WHERE
r.is_counted (comment) a.comment_id = diff.parent_id
AND (comment).local) AS diff; AND diff.child_count != 0;
WITH post_diff AS ( WITH post_diff AS (
UPDATE UPDATE
post_aggregates AS a post_aggregates AS a
SET SET
comments = a.comments + diff.comments, comments = a.comments + diff.comments,
newest_comment_time = GREATEST (a.newest_comment_time, ( newest_comment_time = GREATEST (a.newest_comment_time, diff.newest_comment_time),
SELECT newest_comment_time_necro = GREATEST (a.newest_comment_time_necro, diff.newest_comment_time_necro)
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 ( FROM (
SELECT SELECT
(comment).post_id, post.id AS post_id,
coalesce(sum(count_diff), 0) AS comments coalesce(sum(count_diff), 0) AS comments,
-- Old rows are excluded using `count_diff = 1`
max((comment).published) FILTER (WHERE count_diff = 1) AS newest_comment_time,
max((comment).published) FILTER (WHERE count_diff = 1
-- Ignore comments from the post's creator
AND post.creator_id != (comment).creator_id
-- Ignore comments on old posts
AND post.published > ((comment).published - '2 days'::interval)) AS newest_comment_time_necro,
r.is_counted (post.*) AS include_in_community_aggregates
FROM FROM
select_old_and_new_rows AS old_and_new_rows select_old_and_new_rows AS old_and_new_rows
LEFT JOIN post ON post.id = (comment).post_id
WHERE WHERE
r.is_counted (comment) r.is_counted (comment)
GROUP BY GROUP BY
(comment).post_id) AS diff post.id) AS diff
LEFT JOIN post ON post.id = diff.post_id
WHERE WHERE
a.post_id = diff.post_id a.post_id = diff.post_id
AND (diff.comments,
GREATEST (a.newest_comment_time, diff.newest_comment_time),
GREATEST (a.newest_comment_time_necro, diff.newest_comment_time_necro)) != (0,
a.newest_comment_time,
a.newest_comment_time_necro)
RETURNING RETURNING
a.community_id, a.community_id,
diff.comments, diff.comments,
r.is_counted (post.*) AS include_in_community_aggregates) diff.include_in_community_aggregates)
UPDATE UPDATE
community_aggregates AS a community_aggregates AS a
SET SET
@ -145,7 +192,23 @@ FROM (
GROUP BY GROUP BY
community_id) AS diff community_id) AS diff
WHERE 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; RETURN NULL;
@ -167,20 +230,8 @@ BEGIN
r.is_counted (post) r.is_counted (post)
GROUP BY (post).creator_id) AS diff GROUP BY (post).creator_id) AS diff
WHERE WHERE
a.person_id = diff.creator_id; a.person_id = diff.creator_id
AND diff.post_count != 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;
UPDATE UPDATE
community_aggregates AS a community_aggregates AS a
@ -197,7 +248,23 @@ FROM (
GROUP BY GROUP BY
(post).community_id) AS diff (post).community_id) AS diff
WHERE 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; RETURN NULL;
@ -217,7 +284,9 @@ BEGIN
FROM select_old_and_new_rows AS old_and_new_rows FROM select_old_and_new_rows AS old_and_new_rows
WHERE WHERE
r.is_counted (community) r.is_counted (community)
AND (community).local) AS diff; AND (community).local) AS diff
WHERE
diff.communities != 0;
RETURN NULL; RETURN NULL;
@ -235,7 +304,9 @@ BEGIN
SELECT SELECT
coalesce(sum(count_diff), 0) AS users coalesce(sum(count_diff), 0) AS users
FROM select_old_and_new_rows AS old_and_new_rows 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; RETURN NULL;
@ -270,7 +341,8 @@ BEGIN
GROUP BY GROUP BY
old_post.community_id) AS diff old_post.community_id) AS diff
WHERE WHERE
a.community_id = diff.community_id; a.community_id = diff.community_id
AND diff.comments != 0;
RETURN NULL; RETURN NULL;
END; END;
$$; $$;
@ -296,7 +368,8 @@ BEGIN
LEFT JOIN community ON community.id = (community_follower).community_id 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 LEFT JOIN person ON person.id = (community_follower).person_id GROUP BY (community_follower).community_id) AS diff
WHERE WHERE
a.community_id = diff.community_id; a.community_id = diff.community_id
AND (diff.subscribers, diff.subscribers_local) != (0, 0);
RETURN NULL; RETURN NULL;
@ -474,3 +547,24 @@ CREATE TRIGGER delete_follow
FOR EACH ROW FOR EACH ROW
EXECUTE FUNCTION r.delete_follow_before_person (); EXECUTE FUNCTION r.delete_follow_before_person ();
-- Triggers that change values before insert or update
CREATE FUNCTION r.comment_change_values ()
RETURNS TRIGGER
LANGUAGE plpgsql
AS $$
DECLARE
id text = NEW.id::text;
BEGIN
-- Make `path` end with `id` if it doesn't already
IF NOT (NEW.path ~ ('*.' || id)::lquery) THEN
NEW.path = NEW.path || id;
END IF;
RETURN NEW;
END
$$;
CREATE TRIGGER change_values
BEFORE INSERT OR UPDATE ON comment
FOR EACH ROW
EXECUTE FUNCTION r.comment_change_values ();

73
crates/db_schema/src/impls/comment.rs
View file

@ -15,12 +15,7 @@ use crate::{
utils::{functions::coalesce, get_conn, naive_now, DbPool, DELETED_REPLACEMENT_TEXT}, utils::{functions::coalesce, get_conn, naive_now, DbPool, DELETED_REPLACEMENT_TEXT},
}; };
use chrono::{DateTime, Utc}; use chrono::{DateTime, Utc};
use diesel::{ use diesel::{dsl::insert_into, result::Error, ExpressionMethods, QueryDsl};
dsl::{insert_into, sql_query},
result::Error,
ExpressionMethods,
QueryDsl,
};
use diesel_async::RunQueryDsl; use diesel_async::RunQueryDsl;
use diesel_ltree::Ltree; use diesel_ltree::Ltree;
use url::Url; use url::Url;
@ -72,13 +67,9 @@ impl Comment {
parent_path: Option<&Ltree>, parent_path: Option<&Ltree>,
) -> Result<Comment, Error> { ) -> Result<Comment, Error> {
let conn = &mut get_conn(pool).await?; let conn = &mut get_conn(pool).await?;
let comment_form = (comment_form, parent_path.map(|p| comment::path.eq(p)));
conn if let Some(timestamp) = timestamp {
.build_transaction()
.run(|conn| {
Box::pin(async move {
// Insert, to get the id
let inserted_comment = if let Some(timestamp) = timestamp {
insert_into(comment::table) insert_into(comment::table)
.values(comment_form) .values(comment_form)
.on_conflict(comment::ap_id) .on_conflict(comment::ap_id)
@ -86,68 +77,14 @@ impl Comment {
.do_update() .do_update()
.set(comment_form) .set(comment_form)
.get_result::<Self>(conn) .get_result::<Self>(conn)
.await? .await
} else { } else {
insert_into(comment::table) insert_into(comment::table)
.values(comment_form) .values(comment_form)
.get_result::<Self>(conn) .get_result::<Self>(conn)
.await?
};
let comment_id = inserted_comment.id;
// You need to update the ltree column
let ltree = Ltree(if let Some(parent_path) = parent_path {
// The previous parent will already have 0 in it
// Append this comment id
format!("{}.{}", parent_path.0, comment_id)
} else {
// '0' is always the first path, append to that
format!("{}.{}", 0, comment_id)
});
let updated_comment = diesel::update(comment::table.find(comment_id))
.set(comment::path.eq(ltree))
.get_result::<Self>(conn)
.await?;
// Update the child count for the parent comment_aggregates
// You could do this with a trigger, but since you have to do this manually anyway,
// you can just have it here
if let Some(parent_path) = parent_path {
// You have to update counts for all parents, not just the immediate one
// TODO if the performance of this is terrible, it might be better to do this as part of a
// scheduled query... although the counts would often be wrong.
//
// The child_count query for reference:
// select c.id, c.path, count(c2.id) as child_count from comment c
// left join comment c2 on c2.path <@ c.path and c2.path != c.path
// group by c.id
let parent_id = parent_path.0.split('.').nth(1);
if let Some(parent_id) = parent_id {
let top_parent = format!("0.{}", parent_id);
let update_child_count_stmt = format!(
"
update comment_aggregates ca set child_count = c.child_count
from (
select c.id, c.path, count(c2.id) as child_count from comment c
join comment c2 on c2.path <@ c.path and c2.path != c.path
and c.path <@ '{top_parent}'
group by c.id
) as c
where ca.comment_id = c.id"
);
sql_query(update_child_count_stmt).execute(conn).await?;
}
}
Ok(updated_comment)
}) as _
})
.await .await
} }
}
pub async fn read_from_apub_id( pub async fn read_from_apub_id(
pool: &mut DbPool<'_>, pool: &mut DbPool<'_>,

3
migrations/2024-05-04-140749_separate_triggers/down.sql Normal file
View file

@ -0,0 +1,3 @@
SELECT
1;

4
migrations/2024-05-04-140749_separate_triggers/up.sql Normal file
View file

@ -0,0 +1,4 @@
-- This migration exists to trigger re-execution of replaceable_schema
SELECT
1;