David, Melvin, * David G. Johnston (david.g.johnston@xxxxxxxxx) wrote: > On Monday, April 25, 2016, Melvin Davidson <melvin6925@xxxxxxxxx> 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. There might be some things about system catalogs you can modify, but generally speaking, you can't add a column or otherwise change the structure. System catalogs are represented in memory by C structures (and more), so it's not too surprising that adding a column causes a crash. > 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. Sorry, but as a superuser, there's a lot of things you can do to crash the server, this is just one way. The effort required to prevent anything bad from happening when a user is running as a superuser is far from trivial. In short, no, you can't just add a column to pg_class via SQL, and I don't think we're going to be very interested in trying to "fix" such cases. Thanks! Stephen
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