Re: Clarify "allow_system_table_mods"

On Mon, Apr 25, 2016 at 7:50 PM, David G. Johnston <
david(dot)g(dot)johnston(at)gmail(dot)com> wrote:

> 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.
>

>I doubt it's intended to be opinionated aside from covering all DDL

*So, IOW "*
*Allows modification of the structure of system tables" does not allow
ALTER TABLE ADD column on syscats? That seems a bit contradictory.*

--
*Melvin Davidson*
I reserve the right to fantasize. Whether or not you
wish to share my fantasy is entirely up to you.