On Fri, Apr 12, 2013 at 1:07 PM, Hannu Krosing <ha...@2ndquadrant.com>wrote:
> I was just thinking of moving the queries the pg_dump currently > uses into UDF-s, which do _not_ use catalog cache, but will use > the same SQL to query catalogs as pg_dump currently does > using whatever snapshot mode is currently set . > > the pg_dump will need to still have the same queries for older > versions of postgresql but for new versions pg_dump can become > catalog-agnostic. > > and I think that we can retire pg_dump support for older > postgresql versions the same way we drop support for > older versions of postgresql itself. > main things I see would be > > * get_list_of_objects(object_**type, pattern or namelist) > * get_sql_def_for_object(object_**type, object_name) > * sort_by_dependency(list of [obj_type, obj_name]) > > from this you could easily construct most uses, especially if > sort_by_dependency(list of [obj_type, obj_name]) > would be smart enough to break circular dependencies, like > turning to tables with mutual FK-s into tabledefs without > FKs + separate constraints. > > +1 This is an excellent idea. This would allow doing all kinds of crazy things outside of the scope of pg_dump. 2 years ago I was working on a system to version control the schema, inside the database. Don't know if it's a good idea or not, but one thing which bugged me a lot was the lack of pg_get_[object type]def(oid) functions for all different object types. It also turned out to be quite complicated to do the pg_depend topological sort yourself. I managed eventually, but it was running to slow because I had to pass the entire content of pg_depend to a plperl function I wrote. With this in place I would be motivated enough to resume my old project, which is still online at https://github.com/gluefinance/pov if anyone is interested. Is it really necessary to write all the missing pg_get_[object type]def(oid) functions in C? I think it would be quite easy to put them together using pure SQL, you wouldn't even need PL/pgSQL. This old view I once wrote manage to produce working create and drop statements for most object types using SQL only: https://github.com/gluefinance/pov/blob/master/sql/schema/pov/views/pg_depend_definitions.sql It would also be nice with functions which returned the proper command to DROP an object. I need it in this project in order to do schema modifications where objects have to be dropped/recreated in a particular order to not break dependencies. Perhaps there are other use cases out there.
