Re: Clarify "allow_system_table_mods"

On Monday, April 25, 2016, Melvin Davidson <melvin6925(at)gmail(dot)com> wrote:

> I need clarification on allow_system_table_mods parameter
> Per the documentation:
> *Allows modification of the structure of system tables.* This is used by
> initdb. This parameter can only be set at server start.
>
> However, attempting to modify pg_class to add another column fails with
> "STATUS_ACCESS_VIOLATION" as below.
> So either only certain system catalogs may be changed, or only certain
> types of structure changes are allowed.
> eg: add indexes, triggers
>
> Windows 10
> PostgreSQL 9.2.15, compiled by Visual C++ build 1600, 32-bit
>
> Current user is postgres
> allow_system_table_mods = on
>
> ALTER TABLE pg_catalog.pg_class ADD COLUMN relcreated timestamp DEFAULT
> current_timestamp;
>
> Fails with:
>
> 2016-04-25 12:08:00 EDT STATEMENT: ALTER TABLE pg_catalog.pgclass ADD
> COLUMN relcreated timestamp DEFAULT current_timestamp;
> 2016-04-25 12:08:14 EDT LOG: server process (PID 7760) was terminated by
> exception 0xC0000005
> 2016-04-25 12:08:14 EDT DETAIL: Failed process was running: ALTER TABLE
> pg_catalog.pg_class ADD COLUMN relcreated timestamp DEFAULT
> current_timestamp;
> 2016-04-25 12:08:14 EDT HINT: See C include file "ntstatus.h" for a
> description of the hexadecimal value.
> 2016-04-25 12:08:14 EDT LOG: terminating any other active server processes
>
> From ntstatus.h
> *#define STATUS_ACCESS_VIOLATION ((NTSTATUS)0xC0000005L) //
> winnt*
>
>
If it's going to prevent the action it should be able to do so without
crashing the server..and I doubt it's intended to be opinionated aside from
covering all DDL. What little there is on Google seems to support this.

David J.