EDIT: With thanks to u/code@lemmy.mayes.io, I have a solution for cleaning up the one table that is growing ridiculously in size and that is the activity table. A TRUNCATE activity; command cleaned that right up. A word of caution is in order because the Lemmy instance must be shutdown completely and only the postgres container running if you’re using docker.

As a new Lemmy admin, I think I really need to learn PostgreSQL administration because I need a way to keep my database from ballooning in size and there are no management tools built yet for it. Would someone be so kind as to recommend a good website for learning PostgreSQL? This would also help me maintain my mastodon instance.

  • code@lemmy.mayes.io
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    1 year ago

    Look at vacumn command. Also dbeaver is a teally good gui tool. Right now there is one table thats the main cause (i think its called activity but dont quote me on that there was a post about it)

    That table is mainly for debugging as it logs every action in activitypub your instance does. I truncate it once a week and vacumn it (shrinks the disk space used). Caution. You must shut down lemmy before doing so. I run containers so i stop all except postgres and clean it up.

    • PenguinCoder@beehaw.org
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      1 year ago

      You really don’t want to do a vacuum full on the live DB, it will lock everything. While useful and necessary I think, you have got to plan down time for it. Or your site is going to be inaccessible anyway.

      • PenguinCoder@beehaw.org
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        1 year ago

        Really ugly, but really works. Connect to psql and run:

        WITH RECURSIVE pg_inherit(inhrelid, inhparent) AS
            (select inhrelid, inhparent
            FROM pg_inherits
            UNION
            SELECT child.inhrelid, parent.inhparent
            FROM pg_inherit child, pg_inherits parent
            WHERE child.inhparent = parent.inhrelid),
        pg_inherit_short AS (SELECT * FROM pg_inherit WHERE inhparent NOT IN (SELECT inhrelid FROM pg_inherit))
        SELECT table_schema
            , TABLE_NAME
            , row_estimate
            , pg_size_pretty(total_bytes) AS total
            , pg_size_pretty(index_bytes) AS INDEX
            , pg_size_pretty(toast_bytes) AS toast
            , pg_size_pretty(table_bytes) AS TABLE
            , total_bytes::float8 / sum(total_bytes) OVER () AS total_size_share
          FROM (
            SELECT *, total_bytes-index_bytes-COALESCE(toast_bytes,0) AS table_bytes
            FROM (
                 SELECT c.oid
                      , nspname AS table_schema
                      , relname AS TABLE_NAME
                      , SUM(c.reltuples) OVER (partition BY parent) AS row_estimate
                      , SUM(pg_total_relation_size(c.oid)) OVER (partition BY parent) AS total_bytes
                      , SUM(pg_indexes_size(c.oid)) OVER (partition BY parent) AS index_bytes
                      , SUM(pg_total_relation_size(reltoastrelid)) OVER (partition BY parent) AS toast_bytes
                      , parent
                  FROM (
                        SELECT pg_class.oid
                            , reltuples
                            , relname
                            , relnamespace
                            , pg_class.reltoastrelid
                            , COALESCE(inhparent, pg_class.oid) parent
                        FROM pg_class
                            LEFT JOIN pg_inherit_short ON inhrelid = oid
                        WHERE relkind IN ('r', 'p')
                     ) c
                     LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
          ) a
          WHERE oid = parent
        ) a
        ORDER BY total_bytes DESC LIMIT 3;
        

        That will show the top 3 database tables sizes. I bet you number one is activity.