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In the previous coding, we would look up a relation in RangeVarGetRelid, lock the resulting OID, and then AcceptInvalidationMessages(). While this was sufficient to ensure that we noticed any changes to the relation definition before building the relcache entry, it didn't handle the possibility that the name we looked up no longer referenced the same OID. This was particularly problematic in the case where a table had been dropped and recreated: we'd latch on to the entry for the old relation and fail later on. Now, we acquire the relation lock inside RangeVarGetRelid, and retry the name lookup if we notice that invalidation messages have been processed meanwhile. Many operations that would previously have failed with an error in the presence of concurrent DDL will now succeed. There is a good deal of work remaining to be done here: many callers of RangeVarGetRelid still pass NoLock for one reason or another. In addition, nothing in this patch guards against the possibility that the meaning of an unqualified name might change due to the creation of a relation in a schema earlier in the user's search path than the one where it was previously found. Furthermore, there's nothing at all here to guard against similar race conditions for non-relations. For all that, it's a start. Noah Misch and Robert Haas |
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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/.