RoundSparrow

who would have predicted that Elon Musk would do all the wild things he did with Twitter. Reddit pissing everyone off in June… pretty odd how audiences are behaving in 2023 towards all this. Oh yha, Threads, that coming on the scene too. 2023 has really been odd for audiences.

The SQL speaks for itself, but I don’t know what’s going on in terms of why people are treating social media platforms like Lemmy, Twitter, Threads, Reddit this year so unusually. This SQL statement kind of thing has been covered in so many books, conferences, etc. It’s like forgotten history now in the era of Elon Musk X and Reddit Apollo times.

I don’t know what to say other than I can try to hire a translator or teacher to explain how this SQL problem is obvious and well understood 13 years ago. I mean, there was a whole “NoSQL movement” because of this kind of thing. But I clearly can’t get people to hear past all the Elon Musk, Threads, Lemmy from Reddit … and I’m left describing it as ‘social hazing’ or whatever is gong on with social media.

Lemmy has like 5 different Rust programming communities, but nobody fixing Lemmy. It’s surreal in 2023 the Elon Musk X days. I think it’s making all of us uncomfortable. The social movement underway.

Ok, so let’s look at recent changes that they have deployed… https://github.com/LemmyNet/lemmy/issues/3886

One of which makes entire tree of comments disappear. Do you see developers fretting over this and fixing it? Or do you see them ignoring the May 27 PostgreSQL JOIN problem.

How did such a bug go out? Do you see Lemmy developers actually using Lemmy to test things and notice these crashes and problems? Do you look at their posting and comment history? Do they actually go login over at Beehaw and Lemmy.world and see just how terrible the code performance is?

If it isn’t hazing, what is it?

It’s as if they build a product only for other people to use… and they don’t notice any of the constant crashes, incredibly slow performance etc - and they act like nobody in the computer industry ever heard of Memcache or Redis to solve performance problems. If it isn’t extreme hazing going on, then what is it?

Here, you can dig into what posted days before the pull request you read:

https://github.com/LemmyNet/lemmy/issues/2877#issuecomment-1685314733

June 4:

joins are better than in queries with potentially thousands of inserted IDs.

Given that more than 8 JOIN statements is something PostgreSQL specifically concerns itself with (join_collapse_limit). I hand-edit the query with a single IN clause and the performance problem disappears. 8 full seconds becomes less than 200ms against 5,431,043 posts. And that 200ms is still high, as I was extremely over-reaching with “LIMIT 1000” in case the end-user went wild with blocking lists or some other filtering before reaching the final “LIMIT 10”. When I change it to “LIMIT 20” in the subquery, it drops almost in half to 115ms… still meeting the needs of the outer “LIMIT 10” by double. More of the core query filtering can be put into the IN subquery, as we aren’t dealing with more than 500 length pages (currently limited to 50).

SELECT 
   "post"."id" AS post_id, "post"."name" AS post_title,
   -- "post"."url", "post"."body", "post"."creator_id", "post"."community_id", "post"."removed", "post"."locked", "post"."published", "post"."updated", "post"."deleted", "post"."nsfw", "post"."embed_title", "post"."embed_description", "post"."thumbnail_url",
   -- "post"."ap_id", "post"."local", "post"."embed_video_url", "post"."language_id", "post"."featured_community", "post"."featured_local",
     "person"."id" AS p_id, "person"."name",
     -- "person"."display_name", "person"."avatar", "person"."banned", "person"."published", "person"."updated",
     -- "person"."actor_id", "person"."bio", "person"."local", "person"."private_key", "person"."public_key", "person"."last_refreshed_at", "person"."banner", "person"."deleted", "person"."inbox_url", "person"."shared_inbox_url", "person"."matrix_user_id", "person"."admin",
     -- "person"."bot_account", "person"."ban_expires",
     "person"."instance_id" AS p_inst,
   "community"."id" AS c_id, "community"."name" AS community_name,
   -- "community"."title", "community"."description", "community"."removed", "community"."published", "community"."updated", "community"."deleted",
   -- "community"."nsfw", "community"."actor_id", "community"."local", "community"."private_key", "community"."public_key", "community"."last_refreshed_at", "community"."icon", "community"."banner",
   -- "community"."followers_url", "community"."inbox_url", "community"."shared_inbox_url", "community"."hidden", "community"."posting_restricted_to_mods",
   "community"."instance_id" AS c_inst,
   -- "community"."moderators_url", "community"."featured_url",
     ("community_person_ban"."id" IS NOT NULL) AS ban,
   -- "post_aggregates"."id", "post_aggregates"."post_id", "post_aggregates"."comments", "post_aggregates"."score", "post_aggregates"."upvotes", "post_aggregates"."downvotes", "post_aggregates"."published",
   -- "post_aggregates"."newest_comment_time_necro", "post_aggregates"."newest_comment_time", "post_aggregates"."featured_community", "post_aggregates"."featured_local",
   --"post_aggregates"."hot_rank", "post_aggregates"."hot_rank_active", "post_aggregates"."community_id", "post_aggregates"."creator_id", "post_aggregates"."controversy_rank",
   --  "community_follower"."pending",
   ("post_saved"."id" IS NOT NULL) AS save,
   ("post_read"."id" IS NOT NULL) AS read,
   ("person_block"."id" IS NOT NULL) as block,
   "post_like"."score",
   coalesce(("post_aggregates"."comments" - "person_post_aggregates"."read_comments"), "post_aggregates"."comments") AS unread

FROM (
   ((((((((((
   (
	   (
	   "post_aggregates" 
	   INNER JOIN "person" ON ("post_aggregates"."creator_id" = "person"."id")
	   )
   INNER JOIN "community" ON ("post_aggregates"."community_id" = "community"."id")
   )
   LEFT OUTER JOIN "community_person_ban"
       ON (("post_aggregates"."community_id" = "community_person_ban"."community_id") AND ("community_person_ban"."person_id" = "post_aggregates"."creator_id"))
   )
   INNER JOIN "post" ON ("post_aggregates"."post_id" = "post"."id")
   )
   LEFT OUTER JOIN "community_follower" ON (("post_aggregates"."community_id" = "community_follower"."community_id") AND ("community_follower"."person_id" = 3))
   )
   LEFT OUTER JOIN "community_moderator" ON (("post"."community_id" = "community_moderator"."community_id") AND ("community_moderator"."person_id" = 3))
   )
   LEFT OUTER JOIN "post_saved" ON (("post_aggregates"."post_id" = "post_saved"."post_id") AND ("post_saved"."person_id" = 3))
   )
   LEFT OUTER JOIN "post_read" ON (("post_aggregates"."post_id" = "post_read"."post_id") AND ("post_read"."person_id" = 3))
   )
   LEFT OUTER JOIN "person_block" ON (("post_aggregates"."creator_id" = "person_block"."target_id") AND ("person_block"."person_id" = 3))
   )
   LEFT OUTER JOIN "post_like" ON (("post_aggregates"."post_id" = "post_like"."post_id") AND ("post_like"."person_id" = 3))
   )
   LEFT OUTER JOIN "person_post_aggregates" ON (("post_aggregates"."post_id" = "person_post_aggregates"."post_id") AND ("person_post_aggregates"."person_id" = 3))
   )
   LEFT OUTER JOIN "community_block" ON (("post_aggregates"."community_id" = "community_block"."community_id") AND ("community_block"."person_id" = 3)))
   LEFT OUTER JOIN "local_user_language" ON (("post"."language_id" = "local_user_language"."language_id") AND ("local_user_language"."local_user_id" = 3))
   )
WHERE 
  post_aggregates.id IN (
     SELECT id FROM post_aggregates
     WHERE "post_aggregates"."creator_id" = 3
     ORDER BY "post_aggregates"."featured_local" DESC , "post_aggregates"."published" DESC
     LIMIT 1000
  )
  AND
  (((((((
  (
  (("community"."deleted" = false) AND ("post"."deleted" = false))
  AND ("community"."removed" = false))
  AND ("post"."removed" = false)
  )
  AND ("post_aggregates"."creator_id" = 3)
  )
  AND ("post"."nsfw" = false))
  AND ("community"."nsfw" = false)
  )
  AND ("local_user_language"."language_id" IS NOT NULL)
  )
  AND ("community_block"."person_id" IS NULL)
  )
  AND ("person_block"."person_id" IS NULL)
  )
ORDER BY "post_aggregates"."featured_local" DESC , "post_aggregates"."published" DESC
LIMIT 10
OFFSET 0
;

If it isn’t social hazing, then what is going on here? Why has this issue gone on since May and servers are crashing every day?

. However, I’m far from an expert,

Funny, because I’m a published author and expert on messaging systems… like Lemmy. Iv’e been building them since 1986 professionally.

There was a massive thread I posted dozens of comments on that came before today’s pull request… I suggest you read that too.

Did you notice them even acknowledge server crashes are happening? Do you think developers ever suggest Memcache or Redis? Or discuss how Reddit solved their scaling in 2010 with PostgreSQL?

but perhaps they themselves felt attacked. I know that wasn’t your intention, but misunderstanding happen, especially over text.

I don’t have any trouble understanding a bad SQL statement that has 14 JOINs and being told “JOIN is a distraction” after posting tons of examples.

Do we really need to spoon fed the stuff I did post?

Have you never seen social hazing in action? is it possible that I might be on to something going on psychologically besides my autism?

I can’t believe anyone thinks a server should be crashing with 1 user on it.

may I voice my opinion on the exchange? This is coming from a place of trying to help, since I really do appreciate all the work you’ve put in and are putting in, and the fediverse can really use your talents, so I hope I don’t offend you.

Can you explain to me why it isn’t social hazing?

it didn’t appear that you were being ignored/hazed

Do you know how to read a SQL statement? I just can’t grasp how it isn’t social hazing. I’ve been reading SQL statements for decades, this is obviously a problematic one.

Can you offer alternate explanations of how 3 people could think that SQL statement isn’t … poor performing and gong to cause problems? And how an SQL statement without a WHERE clause took them months to discover and fix?

Extreme hazing is my best answer. I just can’t accept that the SQL statements don’t speak for themselves along with the server crashes. 57K users for 1300 servers is very… taking several seconds to load 10 posts…

Look at the date… May… this has been going on since May. If it isn’t social hazing … what is it? I keep asking myself that.

You’re putting too much importance into this matter. If this is distressing you should let it go and think about something else.

The apologists come out of the woodwork around here who can’t see an SQL statement for what it is, a charade. Anyone who has worked with SQL knows that this is bloated SQL statement and poorly engineered.

I notice the scientific facts of server crashing and SQL statements you won’t discuss, but you sure dish out the social advice for me to “move along” like a Jedi mind trick. Let’s talk about the human attraction to truth and honesty since you are so great at handing out life advice to people. What do you know about the works of Marshall McLuhan on media?

Repeating: Its’ as if the mere concept of Redis or Memcache never existed… and that nobody ever heard of JOIN performance problems. If it isn’t extreme social hazing, what is it?

ild rants. i’ve seen you do this many times. you need to step back, relax, and not take technical feedback so personally

I’ve stepped back and watched them ignore the issue since May when all the servers were crashing. Every single Lemmy server was falling over while they ignored the PostgreSQL problems.

The mistakes are obvious and huge. These are not minor topics.

our comments there are exceptionally aggressive. you accuse the developers of “hazing” you

I think they are hazing the entire World Wide Web, Reddit users, etc. How else can you explain such basic SQL problems that they have allowed to go on for so long?

Its’ as if the mere concept of Redis or Memcache never existed… and that nobody ever heard of JOIN performance problems. If it isn’t extreme social hazing, what is it?

having a meltdown on github doesn’t help anybody.

I’m glad for you that mental control is so trival and you aren’t near death in your life from your brain damage.

Go outside and take a breath

I just got back from dinner ant the months of hazing I’ve witnessed hasn’t gone away. The level of social games being played with PostgreSQL in this project are levels beyond anything I’ve encountered in my 50+ years alive. And I’ve first hand seen Bill Gates and his team do all kinds of odd things to groups.

I am at a total loss to explain why such fundamentals of basic relational database are avoided in this project. If it isn’t social hazing, what is it?

Of course, that would be an insane amount of work, especially if it would get ignored, but something to consider!

I already did an insane amount of work to populate a Lemmy database with over 10 million posts. It is so incredibly slow out of the box that the normal API would take days to accomplish this. i had to rewrite the SQL TRIGGER logic to allow bulk inserts.

Here is my work on that:

DROP TRIGGER site_aggregates_post_insert ON public.post;


/*
TRIGGER will be replaced with per-statement INSERT only
*/
CREATE TRIGGER site_aggregates_post_insert
   AFTER INSERT ON public.post
   REFERENCING NEW TABLE AS new_rows
   FOR EACH STATEMENT
   EXECUTE FUNCTION site_aggregates_post_insert();


DROP TRIGGER community_aggregates_post_count ON public.post;


/*
TRIGGER will be replaced with per-statement INSERT only
*/
CREATE TRIGGER community_aggregates_post_count
   AFTER INSERT ON public.post
   REFERENCING NEW TABLE AS new_rows
   FOR EACH STATEMENT
   EXECUTE FUNCTION community_aggregates_post_count();


DROP TRIGGER person_aggregates_post_count ON public.post;


/*
TRIGGER will be replaced with per-statement INSERT only
*/
CREATE TRIGGER person_aggregates_post_count
   AFTER INSERT ON public.post
   REFERENCING NEW TABLE AS new_rows
   FOR EACH STATEMENT
   EXECUTE FUNCTION person_aggregates_post_count();



/*
TRIGGER will be replaced with per-statement INSERT only
no Lemmy-delete or SQL DELETE to be performed during this period.
*/
CREATE OR REPLACE FUNCTION public.site_aggregates_post_insert() RETURNS trigger
    LANGUAGE plpgsql
    AS $$
BEGIN
   UPDATE site_aggregates SET posts = posts +
      (SELECT count(*) FROM new_rows WHERE local = true)
      WHERE site_id = 1
      ;

   RETURN NULL;
END
$$;


CREATE OR REPLACE FUNCTION public.community_aggregates_post_count() RETURNS trigger
    LANGUAGE plpgsql
    AS $$
BEGIN
        UPDATE
            community_aggregates ca
        SET
            posts = posts + p.new_post_count
        FROM (
            SELECT count(*) AS new_post_count, community_id
            FROM new_rows
            GROUP BY community_id
             ) AS p
        WHERE
            ca.community_id = p.community_id;

    RETURN NULL;
END
$$;


/*
TRIGGER will be replaced with per-statement INSERT only
no Lemmy-delete or SQL DELETE to be performed during this period.
*/
CREATE OR REPLACE FUNCTION public.person_aggregates_post_count() RETURNS trigger
    LANGUAGE plpgsql
    AS $$
BEGIN
        UPDATE
            person_aggregates personagg
        SET
            post_count = post_count + p.new_post_count
        FROM (
            SELECT count(*) AS new_post_count, creator_id
            FROM new_rows
            GROUP BY creator_id
             ) AS p
        WHERE
            personagg.person_id = p.creator_id;

    RETURN NULL;
END
$$;


/*
***********************************************************************************************
** comment table
*/


DROP TRIGGER post_aggregates_comment_count ON public.comment;


/*
TRIGGER will be replaced with per-statement INSERT only
*/
CREATE TRIGGER post_aggregates_comment_count
   AFTER INSERT ON public.comment
   REFERENCING NEW TABLE AS new_rows
   FOR EACH STATEMENT
   EXECUTE FUNCTION post_aggregates_comment_count();


-- IMPORTANT NOTE: this logic for INSERT TRIGGER always assumes that the published datestamp is now(), which was a logical assumption with general use of Lemmy prior to federation being added.
CREATE OR REPLACE FUNCTION public.post_aggregates_comment_count() RETURNS trigger
    LANGUAGE plpgsql
    AS $$
BEGIN

        UPDATE
            -- per statement update 1
            post_aggregates postagg
        SET
            comments = comments + c.new_comment_count
        FROM (
            SELECT count(*) AS new_comment_count, post_id
            FROM new_rows
            GROUP BY post_id
             ) AS c
        WHERE
            postagg.post_id = c.post_id;


        UPDATE
            -- per statement update 2
            post_aggregates postagg
        SET
            newest_comment_time = max_published
        FROM (
            SELECT MAX(published) AS max_published, post_id
            FROM new_rows
            GROUP BY post_id
             ) AS c
        WHERE
            postagg.post_id = c.post_id;

        UPDATE
            -- per statement update 3
            post_aggregates postagg
        SET
            newest_comment_time_necro = max_published
        FROM (
            SELECT MAX(published) AS max_published, post_id, creator_id
            FROM new_rows
            WHERE published > ('now'::timestamp - '2 days'::interval)
            GROUP BY post_id, creator_id
             ) AS c
        WHERE
            postagg.post_id = c.post_id
            AND c.creator_id != postagg.creator_id
            ;

    RETURN NULL;
END
$$;


DROP TRIGGER community_aggregates_comment_count ON public.comment;

CREATE TRIGGER community_aggregates_comment_count
   AFTER INSERT ON public.comment
   REFERENCING NEW TABLE AS new_rows
   FOR EACH STATEMENT
   EXECUTE FUNCTION public.community_aggregates_comment_count();


CREATE OR REPLACE FUNCTION public.community_aggregates_comment_count() RETURNS trigger
    LANGUAGE plpgsql
    AS $$
BEGIN

        UPDATE
            community_aggregates ca
        SET
            comments = comments + p.new_comment_count
        FROM (
            SELECT count(*) AS new_comment_count, community_id
            FROM new_rows AS nr
            JOIN post AS pp ON nr.post_id = pp.id
            GROUP BY pp.community_id
             ) AS p
        WHERE
            ca.community_id = p.community_id
            ;

    RETURN NULL;

END
$$;


DROP TRIGGER person_aggregates_comment_count ON public.comment;

CREATE TRIGGER person_aggregates_comment_count
   AFTER INSERT ON public.comment
   REFERENCING NEW TABLE AS new_rows
   FOR EACH STATEMENT
   EXECUTE FUNCTION public.person_aggregates_comment_count();


CREATE OR REPLACE FUNCTION public.person_aggregates_comment_count() RETURNS trigger
    LANGUAGE plpgsql
    AS $$
BEGIN

        UPDATE
            person_aggregates personagg
        SET
            comment_count = comment_count + p.new_comment_count
        FROM (
            SELECT count(*) AS new_comment_count, creator_id
            FROM new_rows
            GROUP BY creator_id
             ) AS p
        WHERE
            personagg.person_id = p.creator_id;

    RETURN NULL;
END
$$;


DROP TRIGGER site_aggregates_comment_insert ON public.comment;

CREATE TRIGGER site_aggregates_comment_insert
   AFTER INSERT ON public.comment
   REFERENCING NEW TABLE AS new_rows
   FOR EACH STATEMENT
   EXECUTE FUNCTION public.site_aggregates_comment_insert();


CREATE OR REPLACE FUNCTION public.site_aggregates_comment_insert() RETURNS trigger
    LANGUAGE plpgsql
    AS $$
BEGIN

   UPDATE site_aggregates
      SET comments = comments +
         (
            SELECT count(*) FROM new_rows WHERE local = true
         )
      WHERE site_id = 1
      ;

    RETURN NULL;
END
$$;

With this in place, 300,000 posts a minute can be generated and reaching levels of 5 million or 10 million don’t take too long.

I already feel like I have to keep sticking my neck out to get them to question if using the ORM and a dozen JOIN statements isn’t a problem… but I guess I’ll link it: https://github.com/LemmyNet/lemmy/pull/3900

As stated on my Lemmy user profile, I’m “RocketDerp” on GitHiub.

Honestly, the reason I keep making noise is because I’m sick of Lemmy crashing all the time when I come to use it… and I am on many servers that this happens. I really am not trying to piss off the developers, I even said I felt like I am being hazed, and I feel like hazing in general might explain what is going on with how much they are avoiding the elephant in the ROOM that ORM and a dozen JOIN might be the cause! Let alone the lack of Redis or Memcached addition being avoided, that’s a second elephant on the second floor tap-dancing… GitHub Issue 2910 was the straw that broke my back weeks ago, it took months for them to address it when it could be fixed in a couple hours (and it was weeks before the Reddti API deadline at the end of June… and issue 2910 was neglected). The whole thing was a nightmare for me to watch…

First optimization is to not fetch every field and prune it down. For example, it gets public key and private key for every community and user account - then does nothing with them. That’s just pushing data between Rust and PostgreSQL for no reason. That kind of thing is pretty obvious… the huge number of things listed after “SELECT”.

The whole approach is what I recently described as: make a JOIN fusion implosion bomb, then wait for null columns to fall out

There are short-term and long-term solutions. Right now there is already a new feature that will add one more JOIN that is pending merge… “instance blocking” by each single user.

Based on the server overloads and resulting crashes, I think some obvious solutions would be to remove post_aggregates table entirely and just throw more columns on the post table… I’ve seen people do stuff like that. But really you have to have a concept of core foundation.

To me the core foundation of Lemmy data is that people want fresh meat, when world events get into a frenzy, they want to F5 and get the LATEST post and the LATEST comments. Data should have a big wall between the most recent 5 days and everything else. It’s the heart of the beast of human events and a platform like this.

From that perspective, that fresh posts and fresh comments mean everything, you can optimize by just doing a INNER SELECT before any JOIN… or partition the database TABLE into recent and non-recent, or some out-of-band steps to prepare recent data before this SELECT even comes up from an API call… and not let PostgreSQL do so much heavy lifting each page refresh.

I’ve largely given up on pull requests… for sake of sanity. But I waded back in…

I made a pull request today… and I very strategically choose to do it with minimal of features so that it would just go through… and I got lectured that JOIN is never a concern and that filtering based on the core function of the site (presenting fresh meat to readers) was a bad use of the database. I’ve never seen hazing on a project like this. Memcached and Redis should be discussed every day as “why are we not doing what every website does?”, but mum is the word.

Community stuff can work well if done right. For example you don’t see Debian repositories constantly crashing.

I don’t follow your comment, are you suggesting I said something negative about open source project communities? I was talking about the Lemmy social media communities who actually comment and fund the 64-core server upgrades without asking why the site crashes with only 57K users… the people who comment and post on Lemmy… not the “open source” programmer community, but the social media community of Lemmy.

If anyone bothered to actually look at the SQL SELECT that Lemmy uses to list posts every time you hit refresh it would be blindingly obvious how convoluted it is. yet the community does not talk about the programming issues and instead keeps raising money for 64 core hardware upgrades without recognizing just how tiny Lemmy’s database really is and how 57K users is not a large number at all!

your original one, friend. I wouldn’t have argued this point if you had started here.

I mentioned “ORM” right in my first comment.

SELECT 
   "post"."id" AS post_id, "post"."name" AS post_title,
   -- "post"."url", "post"."body", "post"."creator_id", "post"."community_id", "post"."removed", "post"."locked", "post"."published", "post"."updated", "post"."deleted", "post"."nsfw", "post"."embed_title", "post"."embed_description", "post"."thumbnail_url",
   -- "post"."ap_id", "post"."local", "post"."embed_video_url", "post"."language_id", "post"."featured_community", "post"."featured_local",
     "person"."id" AS p_id, "person"."name",
     -- "person"."display_name", "person"."avatar", "person"."banned", "person"."published", "person"."updated",
     -- "person"."actor_id", "person"."bio", "person"."local", "person"."private_key", "person"."public_key", "person"."last_refreshed_at", "person"."banner", "person"."deleted", "person"."inbox_url", "person"."shared_inbox_url", "person"."matrix_user_id", "person"."admin",
     -- "person"."bot_account", "person"."ban_expires",
     "person"."instance_id" AS p_inst,
   "community"."id" AS c_id, "community"."name" AS community_name,
   -- "community"."title", "community"."description", "community"."removed", "community"."published", "community"."updated", "community"."deleted",
   -- "community"."nsfw", "community"."actor_id", "community"."local", "community"."private_key", "community"."public_key", "community"."last_refreshed_at", "community"."icon", "community"."banner",
   -- "community"."followers_url", "community"."inbox_url", "community"."shared_inbox_url", "community"."hidden", "community"."posting_restricted_to_mods",
   "community"."instance_id" AS c_inst,
   -- "community"."moderators_url", "community"."featured_url",
     ("community_person_ban"."id" IS NOT NULL) AS ban,
   -- "post_aggregates"."id", "post_aggregates"."post_id", "post_aggregates"."comments", "post_aggregates"."score", "post_aggregates"."upvotes", "post_aggregates"."downvotes", "post_aggregates"."published",
   -- "post_aggregates"."newest_comment_time_necro", "post_aggregates"."newest_comment_time", "post_aggregates"."featured_community", "post_aggregates"."featured_local",
   --"post_aggregates"."hot_rank", "post_aggregates"."hot_rank_active", "post_aggregates"."community_id", "post_aggregates"."creator_id", "post_aggregates"."controversy_rank",
   --  "community_follower"."pending",
   ("post_saved"."id" IS NOT NULL) AS save,
   ("post_read"."id" IS NOT NULL) AS read,
   ("person_block"."id" IS NOT NULL) as block,
   "post_like"."score",
   coalesce(("post_aggregates"."comments" - "person_post_aggregates"."read_comments"), "post_aggregates"."comments") AS unread

FROM (
   ((((((((((
   (
	   (
	   "post_aggregates" 
	   INNER JOIN "person" ON ("post_aggregates"."creator_id" = "person"."id")
	   )
   INNER JOIN "community" ON ("post_aggregates"."community_id" = "community"."id")
   )
   LEFT OUTER JOIN "community_person_ban"
       ON (("post_aggregates"."community_id" = "community_person_ban"."community_id") AND ("community_person_ban"."person_id" = "post_aggregates"."creator_id"))
   )
   INNER JOIN "post" ON ("post_aggregates"."post_id" = "post"."id")
   )
   LEFT OUTER JOIN "community_follower" ON (("post_aggregates"."community_id" = "community_follower"."community_id") AND ("community_follower"."person_id" = 3))
   )
   LEFT OUTER JOIN "community_moderator" ON (("post"."community_id" = "community_moderator"."community_id") AND ("community_moderator"."person_id" = 3))
   )
   LEFT OUTER JOIN "post_saved" ON (("post_aggregates"."post_id" = "post_saved"."post_id") AND ("post_saved"."person_id" = 3))
   )
   LEFT OUTER JOIN "post_read" ON (("post_aggregates"."post_id" = "post_read"."post_id") AND ("post_read"."person_id" = 3))
   )
   LEFT OUTER JOIN "person_block" ON (("post_aggregates"."creator_id" = "person_block"."target_id") AND ("person_block"."person_id" = 3))
   )
   LEFT OUTER JOIN "post_like" ON (("post_aggregates"."post_id" = "post_like"."post_id") AND ("post_like"."person_id" = 3))
   )
   LEFT OUTER JOIN "person_post_aggregates" ON (("post_aggregates"."post_id" = "person_post_aggregates"."post_id") AND ("person_post_aggregates"."person_id" = 3))
   )
   LEFT OUTER JOIN "community_block" ON (("post_aggregates"."community_id" = "community_block"."community_id") AND ("community_block"."person_id" = 3)))
   LEFT OUTER JOIN "local_user_language" ON (("post"."language_id" = "local_user_language"."language_id") AND ("local_user_language"."local_user_id" = 3))
   )
WHERE (((((((
  ((("community"."deleted" = false) AND ("post"."deleted" = false)) AND ("community"."removed" = false))
  AND ("post"."removed" = false)) AND ("post_aggregates"."creator_id" = 3)) AND ("post"."nsfw" = false))
  AND ("community"."nsfw" = false)) AND ("local_user_language"."language_id" IS NOT NULL))
  AND ("community_block"."person_id" IS NULL))
  AND ("person_block"."person_id" IS NULL))
ORDER BY "post_aggregates"."featured_local" DESC , "post_aggregates"."published" DESC
LIMIT 10
OFFSET 0
;

the people who run Lemmy don’t have the money to support a fleet of failover servers that take over when the main server goes offline.

That has nothing to do with the issue I’m talking about. Every server with the amount of data in them would fail. Doesn’t matter if you had 100 servers on standby.

The Rust logic for database access and PostgreSQL logic in lemmy is unoptimized and there is a serious lack of Diesel programming skills. site_aggregates table had a mistake where 1500 rows were updated for every single new comment and post - and it only got noticed when lemmy.ca was crashing so hard they made a complete copy of the data and studied what was gong on.

Throwing hardware at it, as you describe, has been the other thing… massive numbers of CPU cores. What’s needed is to learn what Reddit did before 2010 with PostgreSQL… as Reddit also used PostgreSQL (and is open source).

That’s basically the only reason you don’t see lots of downtime from major corporations: investment in redundancy,

Downtime because you avoid using Redis or Memcached caching at all costs in your project isn’t common to see in major corporations. But Lemmy avoids caching any data from PostgreSQL at all costs. Been that way for several years. May 17, 2010: “Lesson 5: Memcache;”

As I said in my very first comment, server crashing as a way to scale is a very interesting approach.

EDIT: Freudian slip, “memecached” instead of Memcached

It’s not

It’s really odd how many people around here think the server crashes are perfectly normal and are glad to see newcomers driven away.

Let the servers keep crashing, tell everyone to add new instances to help with performance, which puts 1500 rows into the database tables that used to have 50 rows and invokes a massive federation 1-vote-1-https overhead… causing more crashing… all the while ignoring the SQL design of machine-generated ORM statements and counting logic hidden in the background triggers.

… keep users off your sever as a method of scaling by crashing. It’s one of the more interesting experiences I’ve had this year! And I spent all of February and March with the release of GPT-4… which was also interesting!

How am I supposed to copy everything from those communities

what exactly do you mean to copy? messages, posts and comments from other people?

Are no other servers subscribed to that community and have copies?

If what you want to do is “copy all my communities from current instance to new instance”,

do you mean “copy my list of subscribed communities from one user login to another user login”?

lemmy.ca staff was so frustrated with performance problems a couple weekends ago they cloned a copy of their database Running AUTO_EXPLAIN revealed site_aggregates logic in Lemmy was doing comment = comment + 1 counting against 1500 rows, for every known Lemmy instance in the database, instead of just writing 1 row.