this post was submitted on 03 Jul 2023
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Lemmy Server Performance

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Lemmy Server Performance

lemmy_server uses the Diesel ORM that automatically generates SQL statements. There are serious performance problems in June and July 2023 preventing Lemmy from scaling. Topics include caching, PostgreSQL extensions for troubleshooting, Client/Server Code/SQL Data/server operator apps/sever operator API (performance and storage monitoring), etc.

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Grep the lemmy server code for "= LocalSite::read" - and I find that even for a single vote by an end-user, it is doing an SQL query to the local site settings to see if downvotes are disabled.

Can some Rust programmers chime in here? Can we cache this in RAM and not fetch from SQL every time?

PostgreSQL is telling me that the 2nd most run query on my system, which is receiving incoming federation post/comment/votes, is this:

SELECT "local_site"."id", "local_site"."site_id", "local_site"."site_setup", "local_site"."enable_downvotes", "local_site"."enable_nsfw", "local_site"."community_creation_admin_only", "local_site"."require_email_verification", "local_site"."application_question", "local_site"."private_instance", "local_site"."default_theme", "local_site"."default_post_listing_type", "local_site"."legal_information", "local_site"."hide_modlog_mod_names", "local_site"."application_email_admins", "local_site"."slur_filter_regex", "local_site"."actor_name_max_length", "local_site"."federation_enabled", "local_site"."captcha_enabled", "local_site"."captcha_difficulty", "local_site"."published", "local_site"."updated", "local_site"."registration_mode", "local_site"."reports_email_admins" FROM "local_site" LIMIT $1

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