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