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In the previous coding, it was possible for a relation to be created via CREATE TABLE, CREATE VIEW, CREATE SEQUENCE, CREATE FOREIGN TABLE, etc. in a schema while that schema was meanwhile being concurrently dropped. This led to a pg_class entry with an invalid relnamespace value. The same problem could occur if a relation was moved using ALTER .. SET SCHEMA while the target schema was being concurrently dropped. This patch prevents both of those scenarios by locking the schema to which the relation is being added using AccessShareLock, which conflicts with the AccessExclusiveLock taken by DROP. As a desirable side effect, this also prevents the use of CREATE OR REPLACE VIEW to queue for an AccessExclusiveLock on a relation on which you have no rights: that will now fail immediately with a permissions error, before trying to obtain a lock. We need similar protection for all other object types, but as everything other than relations uses a slightly different set of code paths, I'm leaving that for a separate commit. Original complaint (as far as I could find) about CREATE by Nikhil Sontakke; risk for ALTER .. SET SCHEMA pointed out by Tom Lane; further details by Dan Farina; patch by me; review by Hitoshi Harada.
PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: http://www.postgresql.org/download See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Changes between all PostgreSQL releases are recorded in the file HISTORY. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.