Improve retention policy documentation

[daniel1302]

Issue

People do not understand how to use retention policies in the data-node.

Some comments I shared with node operators

SQLStore.RetentionPeriod is a base/predefined retention policy. There are 3 options:

• forever
• standard
• lite

I would recommend setting it up forever or at least standard, then you can adjust specific tables retention period:

  [[SQLStore.RetentionPolicies]]
    HypertableOrCaggName = "orders"
    DataRetentionPeriod = "30 days"

The orders table is the biggest table so far. It takes 90% of space in postgresql. In our archival nodes, We have 2.5TB of the data there.

See the screen, When I was experimenting with it some time ago.

You can use the following queries to obtain table sizes:

    SELECT
    table_name,
    table_bytes,
    index_bytes,
    toast_bytes,
    total_bytes
    FROM (
        SELECT
          pg_catalog.pg_namespace.nspname           AS schema_name,
          relname                                   AS table_name,
          (hypertable_detailed_size(pg_catalog.pg_class.oid)).*
        FROM pg_catalog.pg_class
          JOIN pg_catalog.pg_namespace ON relnamespace = pg_catalog.pg_namespace.oid
      ) t
    WHERE schema_name = 'public';

    SELECT
    table_name,
    size_bytes
    FROM (
        SELECT
          pg_catalog.pg_namespace.nspname           AS schema_name,
          relname                                   AS table_name,
          pg_relation_size(pg_catalog.pg_class.oid) AS size_bytes
        FROM pg_catalog.pg_class
          JOIN pg_catalog.pg_namespace ON relnamespace = pg_catalog.pg_namespace.oid
      ) t
    WHERE schema_name = 'public';