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.

  • 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.