this post was submitted on 01 Sep 2023
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Threads' New Terms & Conditions Affects the Fediverse (wedistribute.org)
submitted 1 year ago by hedge@beehaw.org to c/technology@beehaw.org
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[–] BitOneZero@beehaw.org 0 points 1 year ago* (last edited 1 year ago) (1 children)

Just because it’s written in Rust doesn’t make your app safe, or performant.

Lemmy 0.18.4 listing posts, frequently via ORM Diesel:

            SELECT "post"."id", "post"."name", "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", "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",
              "community"."id", "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", "community"."moderators_url", "community"."featured_url",
              ("community_person_ban"."id" IS NOT NULL),
              "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),
              ("post_read"."id" IS NOT NULL),
              ("person_block"."id" IS NOT NULL),
              "post_like"."score",
              coalesce(("post_aggregates"."comments" - "person_post_aggregates"."read_comments"),
              "post_aggregates"."comments")
             
              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" = $1))
                )
                LEFT OUTER JOIN "community_moderator" ON (("post"."community_id" = "community_moderator"."community_id") AND ("community_moderator"."person_id" = $1))
                )
                LEFT OUTER JOIN "post_saved" ON (("post_aggregates"."post_id" = "post_saved"."post_id") AND ("post_saved"."person_id" = $1))
                )
                LEFT OUTER JOIN "post_read" ON (("post_aggregates"."post_id" = "post_read"."post_id") AND ("post_read"."person_id" = $1))
                )
                LEFT OUTER JOIN "person_block" ON (("post_aggregates"."creator_id" = "person_block"."target_id") AND ("person_block"."person_id" = $1))
                )
                LEFT OUTER JOIN "post_like" ON (("post_aggregates"."post_id" = "post_like"."post_id") AND ("post_like"."person_id" = $1))
                )
                LEFT OUTER JOIN "person_post_aggregates" ON (("post_aggregates"."post_id" = "person_post_aggregates"."post_id") AND ("person_post_aggregates"."person_id" = $1))
                )
                LEFT OUTER JOIN "community_block" ON (("post_aggregates"."community_id" = "community_block"."community_id") AND ("community_block"."person_id" = $1))
                )
                LEFT OUTER JOIN "local_user_language" ON (("post"."language_id" = "local_user_language"."language_id") AND ("local_user_language"."local_user_id" = $2))
                )
                
                WHERE
                (((
                    (((
                    (
                    ("community"."removed" = $3) AND ("post"."removed" = $4))
                    AND ("community_follower"."pending" IS NOT NULL)
                    )
                    AND ("post"."nsfw" = $5)
                    )
                    AND ("community"."nsfw" = $6)
                    )
                    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"."hot_rank_active" DESC , "post_aggregates"."published" DESC
                    
                LIMIT $7
                OFFSET $8
			;`

That is with hand-optimized person_id = $1, which the Rust code does not do.

[–] anlumo@feddit.de 0 points 1 year ago

This doesn’t look like anything out of the ordinary in a real-world application to me. We have way more complex queries in our service, even though ours are hand crafted.

One thing we did notice though is that sometimes, it’s faster to just query the whole dataset and do the complex filtering in Rust. As soon as you hit the seq scan heuristic in PostgreSQL, there’s nothing to be gained from doing it in SQL.