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My most useful GraphViz hack so far has been a script that reads the schema description out of a PostgreSQL database and turns it into a vaguely Access/SQL Server-like database diagram (a node for each table, arrows representing foreign-key relations).

Someday I'd like to set up a script that takes the query-plan returned by PostgreSQL's EXPLAIN statement and turns it into a diagram with a node for each operation and arrows for dependencies, where the arrow width is proportional to the number of rows involved (again, much like SQL Server's query plan results). This would make it easier to spot the hotspots in a complex plan.

My favourite GraphViz tool would probably be XDot:

    http://code.google.com/p/jrfonseca/wiki/XDot

Fast, interactive viewing of GraphViz source files without having to convert them to PNG every time, and can be embedded in your own Python/GTK+ apps.

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select table_schema, table_schema || '.' || table_name as qualified_table, column_name, data_type from information_schema.columns order by table_schema, table_name, ordinal_position;

select kcu.table_schema, kcu.table_schema || '.' || kcu.table_name as qualified_table, kcu.column_name, ccu.table_schema as referenced_table_schema, ccu.table_schema || '.' || ccu.table_name as referenced_qualified_table, ccu.column_name as referenced_column_name from information_schema.constraint_column_usage as ccu join information_schema.key_column_usage as kcu using (constraint_catalog, constraint_schema, constraint_name) where ccu.table_schema != kcu.table_schema or ccu.table_name != kcu.table_name;