On 21/03/16 23:26, Alvaro Herrera wrote:
Alexander Korotkov wrote:

Thank you for review!

So.  Before this version of the patch was posted in Nov 4th 2015, both
Tom and Heikki had said essentially "CREATE ACCESS METHOD is worthless,
let's pursue this stuff without those commands".
http://www.postgresql.org/message-id/54730dfd.2060...@vmware.com (Nov 2014)
http://www.postgresql.org/message-id/26822.1414516...@sss.pgh.pa.us (Oct 2014)

And in sequence am thread Robert said the opposite.

And then Alexander posted this version, without any discussion that
evidenced that those old objections were overridden.  What happened
here?  Did somebody discuss this in unarchived meetings?  If so, it
would be good to know about that in this thread.

Well there are two main reasons for having DDL, one is dependency tracking and the other is binary upgrade. We can solve part of dependency tracking by recoding dependency between opclass and amhandler instead of opclass and access method, that would work fine. I don't know how to clean pg_am on DROP EXTENSION though without the dependency support.

I also am not sure what is good way of solving binary upgrade without any kind of DDL. Adding another pg_catalog.binary_upgrade_<something> function would be potential solution if we really think DDL is bad idea for access methods in general. Actually thinking of this, we might actually need function like in any case if we are recoding dependencies on access methods (which means it would probably be better to record dependency of opclass on amhandler as mentioned before, since this is already solved for functions and if the oid of am is not referenced anywhere it does not need special handling for binary upgrade).

  Petr Jelinek                  http://www.2ndQuadrant.com/
  PostgreSQL Development, 24x7 Support, Training & Services

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